global secondary indexes

ARCHITECTURE.md

@@ -1,4 +1,5 @@
 ## JormunDB Architecture
+# !!THIS IS NO LONGER ENTIRELY ACCURATE IGNORE OR UPDATE WITH ACCURATE INFO!!
 
 This document explains the internal architecture of JormunDB, including design decisions, storage formats, and the arena-per-request memory management pattern.
 

README.md

@@ -16,7 +16,7 @@
 
 JormunDB is a Self-Hosted DynamoDB replacement that speaks the DynamoDB wire protocol. Point your AWS SDK or CLI at it and use it as a drop-in replacement.
 
-**Why Odin?** The original Zig implementation suffered from explicit allocator threading. Where every function ended up needing an `allocator` parameter and every allocation needed `errdefer` cleanup. Odin's implicit context allocator system eliminates this ceremony. Just one `context.allocator = arena_allocator` at the request handler entry and everything downstream just works.
+**Why Odin?** The original Zig implementation suffered from explicit allocator threading. Where every function ended up needing an `allocator` parameter and every allocation needed `errdefer` cleanup. Odin's implicit context allocator system eliminates this ceremony. Just one `context.allocator = arena_allocator` at the request handler entry and it feels more like working with ctx in Go instead of filling out tax forms.
 
 ## Features
 

TODO.md

@@ -47,22 +47,11 @@ Goal: "aws cli works reliably for CreateTable/ListTables/PutItem/GetItem/DeleteI
 - [x] Expand operator coverage: BETWEEN and begins_with are implemented in parser
 - [x] **Sort key condition filtering in query** — **DONE**: `query()` now accepts optional `Sort_Key_Condition` and applies it (=, <, <=, >, >=, BETWEEN, begins_with)
 
----
+### 5) Service Features
+- [ ] Configuration settings like environment variables for defining users and credentials
+- [ ] Configuration settings for setting up master and replica nodes
 
-## Next (feature parity with Zig + API completeness)
+### 6) Test coverage / tooling
-### 5) UpdateItem / conditional logic groundwork
-- [x] `UpdateItem` handler registered in router (currently returns clear "not yet supported" error)
-- [x] Implement `UpdateItem` (initially minimal: SET for scalar attrs)
-  - [ ] `UpdateItem` needs UPDATED_NEW/UPDATED_OLD response filtering for perfect parity with Dynamo
-- [x] Add `ConditionExpression` support for Put/Delete/Update (start with simple comparisons)
-- [x] Define internal "update plan" representation (parsed ops → applied mutations)
-
-### 6) Response completeness / options
-- [x] `ReturnValues` handling where relevant (NONE/ALL_OLD/UPDATED_NEW etc. — even partial support is useful)
-- [x] `ProjectionExpression` (return subset of attributes)
-- [x] `FilterExpression` (post-query filter for Scan/Query)
-
-### 7) Test coverage / tooling
 - [ ] Add integration tests mirroring AWS CLI script flows:
   - create table → put → get → scan → query → delete
 - [ ] Add fuzz-ish tests for:
@@ -70,39 +59,19 @@ Goal: "aws cli works reliably for CreateTable/ListTables/PutItem/GetItem/DeleteI
   - expression parsing robustness
   - TLV decode failure cases (corrupt bytes)
 
----
+### 7) Secondary indexes
-
-## Later (big features)
-These align with the "Future Enhancements" list in ARCHITECTURE.md.
-
-### 8) Secondary indexes
 - [ ] Global Secondary Indexes (GSI)
 - [ ] Local Secondary Indexes (LSI)
 - [ ] Index backfill + write-path maintenance
 
-### 9) Batch + transactions
+### 8) Performance / ops
-- [x] BatchWriteItem
-- [x] BatchGetItem
-- [ ] Transactions (TransactWriteItems / TransactGetItems)
-
-### 10) Performance / ops
 - [ ] Connection reuse / keep-alive tuning
 - [ ] Bloom filters / RocksDB options tuning for common patterns
 - [ ] Optional compression policy (LZ4/Zstd knobs)
 - [ ] Parallel scan (segment scanning)
 
----
+### 9) Replication / WAL
-
-## Replication / WAL
 (There is a C++ shim stubbed out for WAL iteration and applying write batches.)
 - [ ] Implement WAL iterator: `latest_sequence`, `wal_iter_next` returning writebatch blob
 - [ ] Implement apply-writebatch on follower
 - [ ] Add a minimal replication test harness (leader generates N ops → follower applies → compare)
-
----
-
-## Housekeeping
-- [x] Fix TODO hygiene: keep this file short and "actionable"
-  - Added "Bug Fixes Applied" section documenting what changed and why
-- [ ] Add a CONTRIBUTING quick checklist (allocator rules, formatting, tests)
-- [ ] Add "known limitations" section in README (unsupported DynamoDB features)

dynamodb/gsi.odin

@@ -0,0 +1,481 @@
+// Global Secondary Index (GSI) support
+//
+// DynamoDB GSI semantics:
+//   - GSI entries are maintained automatically on every write (put/delete/update)
+//   - Each GSI has its own key schema (partition key + optional sort key)
+//   - GSI keys are built from item attributes; if an item doesn't have the GSI
+//     key attribute(s), NO GSI entry is written (sparse index)
+//   - Projection controls which non-key attributes are stored in the GSI entry:
+//       ALL       → entire item is copied
+//       KEYS_ONLY → only table PK/SK + GSI PK/SK
+//       INCLUDE   → table keys + GSI keys + specified non-key attributes
+//   - Query on a GSI uses IndexName to route to the correct key prefix
+//
+// Storage layout:
+//   GSI key:   [0x03][table_name][index_name][gsi_pk_value][gsi_sk_value?]
+//   GSI value: TLV-encoded projected item (same binary format as regular items)
+//
+// Write path:
+//   put_item  → for each GSI, extract GSI key attrs from the NEW item, write GSI entry
+//   delete    → for each GSI, extract GSI key attrs from the OLD item, delete GSI entry
+//   update    → delete OLD GSI entries, write NEW GSI entries
+//
+package dynamodb
+
+import "core:slice"
+import "core:strings"
+import "../rocksdb"
+
+// ============================================================================
+// GSI Key Extraction
+//
+// Extracts the GSI partition key (and optional sort key) raw bytes from an item.
+// Returns false if the item doesn't have the required GSI PK attribute (sparse).
+// ============================================================================
+
+GSI_Key_Values :: struct {
+	pk:  []byte,
+	sk:  Maybe([]byte),
+}
+
+// Extract GSI key values from an item based on the GSI's key schema.
+// Returns ok=false if the required partition key attribute is missing (sparse index).
+gsi_extract_key_values :: proc(item: Item, gsi_key_schema: []Key_Schema_Element) -> (GSI_Key_Values, bool) {
+	result: GSI_Key_Values
+
+	for ks in gsi_key_schema {
+		attr, found := item[ks.attribute_name]
+		if !found {
+			if ks.key_type == .HASH {
+				return {}, false // PK missing → sparse, skip this GSI entry
+			}
+			continue // SK missing is OK, just no SK segment
+		}
+
+		raw, raw_ok := attr_value_to_bytes(attr)
+		if !raw_ok {
+			if ks.key_type == .HASH {
+				return {}, false
+			}
+			continue
+		}
+
+		switch ks.key_type {
+		case .HASH:
+			result.pk = raw
+		case .RANGE:
+			result.sk = raw
+		}
+	}
+
+	return result, true
+}
+
+// Convert a scalar attribute value to its raw byte representation (borrowed).
+attr_value_to_bytes :: proc(attr: Attribute_Value) -> ([]byte, bool) {
+	#partial switch v in attr {
+	case String:
+		return transmute([]byte)string(v), true
+	case Number:
+		return transmute([]byte)string(v), true
+	case Binary:
+		return transmute([]byte)string(v), true
+	}
+	return nil, false
+}
+
+// ============================================================================
+// GSI Projection
+//
+// Build a projected copy of an item for storage in a GSI entry.
+// ============================================================================
+
+// Build the projected item for a GSI entry.
+// The result is a new Item that the caller owns.
+gsi_project_item :: proc(
+	item: Item,
+	gsi: ^Global_Secondary_Index,
+	table_key_schema: []Key_Schema_Element,
+) -> Item {
+	switch gsi.projection.projection_type {
+	case .ALL:
+		return item_deep_copy(item)
+
+	case .KEYS_ONLY:
+		projected := make(Item)
+		// Include table key attributes
+		for ks in table_key_schema {
+			if val, found := item[ks.attribute_name]; found {
+				projected[strings.clone(ks.attribute_name)] = attr_value_deep_copy(val)
+			}
+		}
+		// Include GSI key attributes
+		for ks in gsi.key_schema {
+			if _, already := projected[ks.attribute_name]; already {
+				continue // Already included as table key
+			}
+			if val, found := item[ks.attribute_name]; found {
+				projected[strings.clone(ks.attribute_name)] = attr_value_deep_copy(val)
+			}
+		}
+		return projected
+
+	case .INCLUDE:
+		projected := make(Item)
+		// Include table key attributes
+		for ks in table_key_schema {
+			if val, found := item[ks.attribute_name]; found {
+				projected[strings.clone(ks.attribute_name)] = attr_value_deep_copy(val)
+			}
+		}
+		// Include GSI key attributes
+		for ks in gsi.key_schema {
+			if _, already := projected[ks.attribute_name]; already {
+				continue
+			}
+			if val, found := item[ks.attribute_name]; found {
+				projected[strings.clone(ks.attribute_name)] = attr_value_deep_copy(val)
+			}
+		}
+		// Include specified non-key attributes
+		if nka, has_nka := gsi.projection.non_key_attributes.?; has_nka {
+			for attr_name in nka {
+				if _, already := projected[attr_name]; already {
+					continue
+				}
+				if val, found := item[attr_name]; found {
+					projected[strings.clone(attr_name)] = attr_value_deep_copy(val)
+				}
+			}
+		}
+		return projected
+	}
+
+	// Fallback: all
+	return item_deep_copy(item)
+}
+
+// ============================================================================
+// GSI Write Maintenance
+//
+// Called after a successful data write to maintain GSI entries.
+// Uses WriteBatch for atomicity (all GSI entries for one item in one batch).
+// ============================================================================
+
+// Write GSI entries for an item across all GSIs defined on the table.
+// Should be called AFTER the main data key is written.
+gsi_write_entries :: proc(
+	engine: ^Storage_Engine,
+	table_name: string,
+	item: Item,
+	metadata: ^Table_Metadata,
+) -> Storage_Error {
+	gsis, has_gsis := metadata.global_secondary_indexes.?
+	if !has_gsis || len(gsis) == 0 {
+		return .None
+	}
+
+	for &gsi in gsis {
+		// Extract GSI key from item
+		gsi_kv, kv_ok := gsi_extract_key_values(item, gsi.key_schema)
+		if !kv_ok {
+			continue // Sparse: item doesn't have GSI PK, skip
+		}
+
+		// Build GSI storage key
+		gsi_storage_key := build_gsi_key(table_name, gsi.index_name, gsi_kv.pk, gsi_kv.sk)
+		defer delete(gsi_storage_key)
+
+		// Build projected item
+		projected := gsi_project_item(item, &gsi, metadata.key_schema)
+		defer item_destroy(&projected)
+
+		// Encode projected item
+		encoded, encode_ok := encode(projected)
+		if !encode_ok {
+			return .Serialization_Error
+		}
+		defer delete(encoded)
+
+		// Write to RocksDB
+		put_err := rocksdb.db_put(&engine.db, gsi_storage_key, encoded)
+		if put_err != .None {
+			return .RocksDB_Error
+		}
+	}
+
+	return .None
+}
+
+// Delete GSI entries for an item across all GSIs.
+// Should be called BEFORE or AFTER the main data key is deleted.
+// Needs the OLD item to know which GSI keys to remove.
+gsi_delete_entries :: proc(
+	engine: ^Storage_Engine,
+	table_name: string,
+	old_item: Item,
+	metadata: ^Table_Metadata,
+) -> Storage_Error {
+	gsis, has_gsis := metadata.global_secondary_indexes.?
+	if !has_gsis || len(gsis) == 0 {
+		return .None
+	}
+
+	for &gsi in gsis {
+		gsi_kv, kv_ok := gsi_extract_key_values(old_item, gsi.key_schema)
+		if !kv_ok {
+			continue // Item didn't have a GSI entry
+		}
+
+		gsi_storage_key := build_gsi_key(table_name, gsi.index_name, gsi_kv.pk, gsi_kv.sk)
+		defer delete(gsi_storage_key)
+
+		del_err := rocksdb.db_delete(&engine.db, gsi_storage_key)
+		if del_err != .None {
+			return .RocksDB_Error
+		}
+	}
+
+	return .None
+}
+
+// ============================================================================
+// GSI Query
+//
+// Queries a GSI by partition key with optional sort key condition.
+// Mirrors the main table query() but uses GSI key prefix.
+// ============================================================================
+
+gsi_query :: proc(
+	engine: ^Storage_Engine,
+	table_name: string,
+	index_name: string,
+	partition_key_value: []byte,
+	exclusive_start_key: Maybe([]byte),
+	limit: int,
+	sk_condition: Maybe(Sort_Key_Condition) = nil,
+) -> (Query_Result, Storage_Error) {
+	// Build GSI partition prefix
+	prefix := build_gsi_partition_prefix(table_name, index_name, partition_key_value)
+	defer delete(prefix)
+
+	iter, iter_err := rocksdb.iter_create(&engine.db)
+	if iter_err != .None {
+		return {}, .RocksDB_Error
+	}
+	defer rocksdb.iter_destroy(&iter)
+
+	max_items := limit if limit > 0 else 1_000_000
+
+	// Seek to start position
+	if start_key, has_start := exclusive_start_key.?; has_start {
+		if has_prefix(start_key, prefix) {
+			rocksdb.iter_seek(&iter, start_key)
+			if rocksdb.iter_valid(&iter) {
+				rocksdb.iter_next(&iter)
+			}
+		} else {
+			rocksdb.iter_seek(&iter, prefix)
+		}
+	} else {
+		rocksdb.iter_seek(&iter, prefix)
+	}
+
+	items := make([dynamic]Item)
+	count := 0
+	last_key: Maybe([]byte) = nil
+	has_more := false
+
+	for rocksdb.iter_valid(&iter) {
+		key := rocksdb.iter_key(&iter)
+		if key == nil || !has_prefix(key, prefix) {
+			break
+		}
+
+		if count >= max_items {
+			has_more = true
+			break
+		}
+
+		value := rocksdb.iter_value(&iter)
+		if value == nil {
+			rocksdb.iter_next(&iter)
+			continue
+		}
+
+		item, decode_ok := decode(value)
+		if !decode_ok {
+			rocksdb.iter_next(&iter)
+			continue
+		}
+
+		// Sort key condition filtering
+		if skc, has_skc := sk_condition.?; has_skc {
+			if !evaluate_sort_key_condition(item, &skc) {
+				item_copy := item
+				item_destroy(&item_copy)
+				rocksdb.iter_next(&iter)
+				continue
+			}
+		}
+
+		append(&items, item)
+		count += 1
+
+		// Track key of last returned item
+		if prev_key, had_prev := last_key.?; had_prev {
+			delete(prev_key)
+		}
+		last_key = slice.clone(key)
+
+		rocksdb.iter_next(&iter)
+	}
+
+	// Only emit LastEvaluatedKey if there are more items
+	if !has_more {
+		if lk, had_lk := last_key.?; had_lk {
+			delete(lk)
+		}
+		last_key = nil
+	}
+
+	result_items := make([]Item, len(items))
+	copy(result_items, items[:])
+
+	return Query_Result{
+		items              = result_items,
+		last_evaluated_key = last_key,
+	}, .None
+}
+
+// ============================================================================
+// GSI Scan
+//
+// Scans all entries in a GSI (all partition keys under that index).
+// ============================================================================
+
+gsi_scan :: proc(
+	engine: ^Storage_Engine,
+	table_name: string,
+	index_name: string,
+	exclusive_start_key: Maybe([]byte),
+	limit: int,
+) -> (Scan_Result, Storage_Error) {
+	prefix := build_gsi_prefix(table_name, index_name)
+	defer delete(prefix)
+
+	iter, iter_err := rocksdb.iter_create(&engine.db)
+	if iter_err != .None {
+		return {}, .RocksDB_Error
+	}
+	defer rocksdb.iter_destroy(&iter)
+
+	max_items := limit if limit > 0 else 1_000_000
+
+	if start_key, has_start := exclusive_start_key.?; has_start {
+		if has_prefix(start_key, prefix) {
+			rocksdb.iter_seek(&iter, start_key)
+			if rocksdb.iter_valid(&iter) {
+				rocksdb.iter_next(&iter)
+			}
+		} else {
+			rocksdb.iter_seek(&iter, prefix)
+		}
+	} else {
+		rocksdb.iter_seek(&iter, prefix)
+	}
+
+	items := make([dynamic]Item)
+	count := 0
+	last_key: Maybe([]byte) = nil
+	has_more := false
+
+	for rocksdb.iter_valid(&iter) {
+		key := rocksdb.iter_key(&iter)
+		if key == nil || !has_prefix(key, prefix) {
+			break
+		}
+
+		if count >= max_items {
+			has_more = true
+			break
+		}
+
+		value := rocksdb.iter_value(&iter)
+		if value == nil {
+			rocksdb.iter_next(&iter)
+			continue
+		}
+
+		item, decode_ok := decode(value)
+		if !decode_ok {
+			rocksdb.iter_next(&iter)
+			continue
+		}
+
+		append(&items, item)
+		count += 1
+
+		if prev_key, had_prev := last_key.?; had_prev {
+			delete(prev_key)
+		}
+		last_key = slice.clone(key)
+
+		rocksdb.iter_next(&iter)
+	}
+
+	if !has_more {
+		if lk, had_lk := last_key.?; had_lk {
+			delete(lk)
+		}
+		last_key = nil
+	}
+
+	result_items := make([]Item, len(items))
+	copy(result_items, items[:])
+
+	return Scan_Result{
+		items              = result_items,
+		last_evaluated_key = last_key,
+	}, .None
+}
+
+// ============================================================================
+// GSI Metadata Lookup Helpers
+// ============================================================================
+
+// Find a GSI definition by index name in the table metadata.
+find_gsi :: proc(metadata: ^Table_Metadata, index_name: string) -> (^Global_Secondary_Index, bool) {
+	gsis, has_gsis := metadata.global_secondary_indexes.?
+	if !has_gsis {
+		return nil, false
+	}
+
+	for &gsi in gsis {
+		if gsi.index_name == index_name {
+			return &gsi, true
+		}
+	}
+
+	return nil, false
+}
+
+// Get the GSI's sort key attribute name (if any).
+gsi_get_sort_key_name :: proc(gsi: ^Global_Secondary_Index) -> Maybe(string) {
+	for ks in gsi.key_schema {
+		if ks.key_type == .RANGE {
+			return ks.attribute_name
+		}
+	}
+	return nil
+}
+
+// Get the GSI's partition key attribute name.
+gsi_get_partition_key_name :: proc(gsi: ^Global_Secondary_Index) -> Maybe(string) {
+	for ks in gsi.key_schema {
+		if ks.key_type == .HASH {
+			return ks.attribute_name
+		}
+	}
+	return nil
+}

dynamodb/gsi_metadata.odin

@@ -0,0 +1,187 @@
+// gsi_metadata.odin — GSI metadata parsing for serialize/deserialize_table_metadata
+//
+// Parses GSI definitions from the embedded JSON string stored in table metadata.
+// This file lives in the dynamodb/ package.
+package dynamodb
+
+import "core:encoding/json"
+import "core:mem"
+import "core:strings"
+
+// Parse GlobalSecondaryIndexes from a JSON string like:
+// [{"IndexName":"email-index","KeySchema":[{"AttributeName":"email","KeyType":"HASH"}],
+//   "Projection":{"ProjectionType":"ALL"}}]
+//
+// Allocates all strings with the given allocator (engine.allocator for long-lived data).
+parse_gsis_json :: proc(json_str: string, allocator: mem.Allocator) -> ([]Global_Secondary_Index, bool) {
+	data, parse_err := json.parse(transmute([]byte)json_str, allocator = context.temp_allocator)
+	if parse_err != nil {
+		return nil, false
+	}
+	defer json.destroy_value(data)
+
+	arr, ok := data.(json.Array)
+	if !ok {
+		return nil, false
+	}
+
+	if len(arr) == 0 {
+		return nil, true // Empty is valid
+	}
+
+	result := make([]Global_Secondary_Index, len(arr), allocator)
+
+	for elem, i in arr {
+		obj, obj_ok := elem.(json.Object)
+		if !obj_ok {
+			cleanup_gsis(result[:i], allocator)
+			delete(result, allocator)
+			return nil, false
+		}
+
+		gsi, gsi_ok := parse_single_gsi_json(obj, allocator)
+		if !gsi_ok {
+			cleanup_gsis(result[:i], allocator)
+			delete(result, allocator)
+			return nil, false
+		}
+
+		result[i] = gsi
+	}
+
+	return result, true
+}
+
+// Parse a single GSI object from JSON
+@(private = "file")
+parse_single_gsi_json :: proc(obj: json.Object, allocator: mem.Allocator) -> (Global_Secondary_Index, bool) {
+	gsi: Global_Secondary_Index
+
+	// IndexName
+	idx_val, idx_found := obj["IndexName"]
+	if !idx_found {
+		return {}, false
+	}
+	idx_str, idx_ok := idx_val.(json.String)
+	if !idx_ok {
+		return {}, false
+	}
+	gsi.index_name = strings.clone(string(idx_str), allocator)
+
+	// KeySchema
+	ks_val, ks_found := obj["KeySchema"]
+	if !ks_found {
+		delete(gsi.index_name, allocator)
+		return {}, false
+	}
+	ks_arr, ks_ok := ks_val.(json.Array)
+	if !ks_ok || len(ks_arr) == 0 || len(ks_arr) > 2 {
+		delete(gsi.index_name, allocator)
+		return {}, false
+	}
+
+	key_schema := make([]Key_Schema_Element, len(ks_arr), allocator)
+	for ks_elem, j in ks_arr {
+		ks_obj, kobj_ok := ks_elem.(json.Object)
+		if !kobj_ok {
+			for k in 0..<j {
+				delete(key_schema[k].attribute_name, allocator)
+			}
+			delete(key_schema, allocator)
+			delete(gsi.index_name, allocator)
+			return {}, false
+		}
+
+		an_val, an_found := ks_obj["AttributeName"]
+		if !an_found {
+			for k in 0..<j { delete(key_schema[k].attribute_name, allocator) }
+			delete(key_schema, allocator)
+			delete(gsi.index_name, allocator)
+			return {}, false
+		}
+		an_str, an_ok := an_val.(json.String)
+		if !an_ok {
+			for k in 0..<j { delete(key_schema[k].attribute_name, allocator) }
+			delete(key_schema, allocator)
+			delete(gsi.index_name, allocator)
+			return {}, false
+		}
+
+		kt_val, kt_found := ks_obj["KeyType"]
+		if !kt_found {
+			for k in 0..<j { delete(key_schema[k].attribute_name, allocator) }
+			delete(key_schema, allocator)
+			delete(gsi.index_name, allocator)
+			return {}, false
+		}
+		kt_str, kt_ok := kt_val.(json.String)
+		if !kt_ok {
+			for k in 0..<j { delete(key_schema[k].attribute_name, allocator) }
+			delete(key_schema, allocator)
+			delete(gsi.index_name, allocator)
+			return {}, false
+		}
+
+		kt, kt_parse_ok := key_type_from_string(string(kt_str))
+		if !kt_parse_ok {
+			for k in 0..<j { delete(key_schema[k].attribute_name, allocator) }
+			delete(key_schema, allocator)
+			delete(gsi.index_name, allocator)
+			return {}, false
+		}
+
+		key_schema[j] = Key_Schema_Element{
+			attribute_name = strings.clone(string(an_str), allocator),
+			key_type = kt,
+		}
+	}
+	gsi.key_schema = key_schema
+
+	// Projection
+	gsi.projection.projection_type = .ALL // default
+	if proj_val, proj_found := obj["Projection"]; proj_found {
+		if proj_obj, proj_ok := proj_val.(json.Object); proj_ok {
+			if pt_val, pt_found := proj_obj["ProjectionType"]; pt_found {
+				if pt_str, pt_ok := pt_val.(json.String); pt_ok {
+					switch string(pt_str) {
+					case "ALL":       gsi.projection.projection_type = .ALL
+					case "KEYS_ONLY": gsi.projection.projection_type = .KEYS_ONLY
+					case "INCLUDE":   gsi.projection.projection_type = .INCLUDE
+					}
+				}
+			}
+
+			// NonKeyAttributes
+			if nka_val, nka_found := proj_obj["NonKeyAttributes"]; nka_found {
+				if nka_arr, nka_ok := nka_val.(json.Array); nka_ok && len(nka_arr) > 0 {
+					nka := make([]string, len(nka_arr), allocator)
+					for attr_val, k in nka_arr {
+						if attr_str, attr_ok := attr_val.(json.String); attr_ok {
+							nka[k] = strings.clone(string(attr_str), allocator)
+						}
+					}
+					gsi.projection.non_key_attributes = nka
+				}
+			}
+		}
+	}
+
+	return gsi, true
+}
+
+// Clean up partially-constructed GSI array
+cleanup_gsis :: proc(gsis: []Global_Secondary_Index, allocator: mem.Allocator) {
+	for gsi in gsis {
+		delete(gsi.index_name, allocator)
+		for ks in gsi.key_schema {
+			delete(ks.attribute_name, allocator)
+		}
+		delete(gsi.key_schema, allocator)
+		if nka, has_nka := gsi.projection.non_key_attributes.?; has_nka {
+			for attr in nka {
+				delete(attr, allocator)
+			}
+			delete(nka, allocator)
+		}
+	}
+}

dynamodb/key_codec_gsi.odin

@@ -0,0 +1,94 @@
+// key_codec_gsi.odin — Additional key codec functions for GSI support
+//
+// These procedures complement key_codec.odin with prefix builders needed
+// for GSI scanning and querying. They follow the same encoding conventions:
+//   [entity_type][varint_len][segment_bytes]...
+//
+// Add the contents of this file to key_codec.odin (or keep as a separate file
+// in the dynamodb/ package).
+package dynamodb
+
+import "core:bytes"
+
+// Build GSI index prefix for scanning all entries in a GSI:
+//   [gsi][table_name][index_name]
+build_gsi_prefix :: proc(table_name: string, index_name: string) -> []byte {
+	buf: bytes.Buffer
+	bytes.buffer_init_allocator(&buf, 0, 256, context.allocator)
+
+	bytes.buffer_write_byte(&buf, u8(Entity_Type.GSI))
+
+	encode_varint(&buf, len(table_name))
+	bytes.buffer_write_string(&buf, table_name)
+
+	encode_varint(&buf, len(index_name))
+	bytes.buffer_write_string(&buf, index_name)
+
+	return bytes.buffer_to_bytes(&buf)
+}
+
+// Build GSI partition prefix for querying within a single partition:
+//   [gsi][table_name][index_name][pk_value]
+build_gsi_partition_prefix :: proc(table_name: string, index_name: string, pk_value: []byte) -> []byte {
+	buf: bytes.Buffer
+	bytes.buffer_init_allocator(&buf, 0, 512, context.allocator)
+
+	bytes.buffer_write_byte(&buf, u8(Entity_Type.GSI))
+
+	encode_varint(&buf, len(table_name))
+	bytes.buffer_write_string(&buf, table_name)
+
+	encode_varint(&buf, len(index_name))
+	bytes.buffer_write_string(&buf, index_name)
+
+	encode_varint(&buf, len(pk_value))
+	bytes.buffer_write(&buf, pk_value)
+
+	return bytes.buffer_to_bytes(&buf)
+}
+
+// Decode a GSI key back into components
+Decoded_GSI_Key :: struct {
+	table_name: string,
+	index_name: string,
+	pk_value:   []byte,
+	sk_value:   Maybe([]byte),
+}
+
+decode_gsi_key :: proc(key: []byte) -> (result: Decoded_GSI_Key, ok: bool) {
+	decoder := Key_Decoder{data = key, pos = 0}
+
+	entity_type := decoder_read_entity_type(&decoder) or_return
+	if entity_type != .GSI {
+		return {}, false
+	}
+
+	table_name_bytes := decoder_read_segment(&decoder) or_return
+	result.table_name = string(table_name_bytes)
+
+	index_name_bytes := decoder_read_segment(&decoder) or_return
+	result.index_name = string(index_name_bytes)
+
+	result.pk_value = decoder_read_segment(&decoder) or_return
+
+	if decoder_has_more(&decoder) {
+		sk := decoder_read_segment(&decoder) or_return
+		result.sk_value = sk
+	}
+
+	return result, true
+}
+
+// Build GSI prefix for deleting all GSI entries for a table (used by delete_table)
+//   [gsi][table_name]
+build_gsi_table_prefix :: proc(table_name: string) -> []byte {
+	buf: bytes.Buffer
+	bytes.buffer_init_allocator(&buf, 0, 256, context.allocator)
+
+	bytes.buffer_write_byte(&buf, u8(Entity_Type.GSI))
+
+	encode_varint(&buf, len(table_name))
+	bytes.buffer_write_string(&buf, table_name)
+
+	return bytes.buffer_to_bytes(&buf)
+}

dynamodb/storage.odin

@@ -84,7 +84,23 @@ table_metadata_destroy :: proc(metadata: ^Table_Metadata, allocator: mem.Allocat
 	}
 	delete(metadata.attribute_definitions, allocator)
 
-	// TODO: Free GSI/LSI if we implement them
+	// Free GSI definitions
+	if gsis, has_gsis := metadata.global_secondary_indexes.?; has_gsis {
+		for gsi in gsis {
+			delete(gsi.index_name, allocator)
+			for ks in gsi.key_schema {
+				delete(ks.attribute_name, allocator)
+			}
+			delete(gsi.key_schema, allocator)
+			if nka, has_nka := gsi.projection.non_key_attributes.?; has_nka {
+				for attr in nka {
+					delete(attr, allocator)
+				}
+				delete(nka, allocator)
+			}
+		}
+		delete(gsis, allocator)
+	}
 }
 
 // Get the partition key attribute name
@@ -187,7 +203,6 @@ remove_table_lock :: proc(engine: ^Storage_Engine, table_name: string) {
 
 // Serialize table metadata to binary format
 serialize_table_metadata :: proc(metadata: ^Table_Metadata) -> ([]byte, bool) {
-	// Create a temporary item to hold metadata
 	meta_item := make(Item, context.temp_allocator)
 	defer delete(meta_item)
 
@@ -200,7 +215,7 @@ serialize_table_metadata :: proc(metadata: ^Table_Metadata) -> ([]byte, bool) {
 		if i > 0 {
 			strings.write_string(&ks_builder, ",")
 		}
-		fmt.sbprintf(&ks_builder, `{"AttributeName":"%s","KeyType":"%s"}`,
+		fmt.sbprintf(&ks_builder, `{{"AttributeName":"%s","KeyType":"%s"}}`,
 			ks.attribute_name, key_type_to_string(ks.key_type))
 	}
 	strings.write_string(&ks_builder, "]")
@@ -216,7 +231,7 @@ serialize_table_metadata :: proc(metadata: ^Table_Metadata) -> ([]byte, bool) {
 		if i > 0 {
 			strings.write_string(&ad_builder, ",")
 		}
-		fmt.sbprintf(&ad_builder, `{"AttributeName":"%s","AttributeType":"%s"}`,
+		fmt.sbprintf(&ad_builder, `{{"AttributeName":"%s","AttributeType":"%s"}}`,
 			ad.attribute_name, scalar_type_to_string(ad.attribute_type))
 	}
 	strings.write_string(&ad_builder, "]")
@@ -227,6 +242,48 @@ serialize_table_metadata :: proc(metadata: ^Table_Metadata) -> ([]byte, bool) {
 	meta_item["TableStatus"] = String(strings.clone(table_status_to_string(metadata.table_status)))
 	meta_item["CreationDateTime"] = Number(fmt.aprint(metadata.creation_date_time))
 
+	// Encode GSI definitions as JSON string
+	if gsis, has_gsis := metadata.global_secondary_indexes.?; has_gsis && len(gsis) > 0 {
+		gsi_builder := strings.builder_make(context.temp_allocator)
+		defer strings.builder_destroy(&gsi_builder)
+
+		strings.write_string(&gsi_builder, "[")
+		for gsi, i in gsis {
+			if i > 0 {
+				strings.write_string(&gsi_builder, ",")
+			}
+			fmt.sbprintf(&gsi_builder, `{{"IndexName":"%s","KeySchema":[`, gsi.index_name)
+			for ks, j in gsi.key_schema {
+				if j > 0 {
+					strings.write_string(&gsi_builder, ",")
+				}
+				fmt.sbprintf(&gsi_builder, `{{"AttributeName":"%s","KeyType":"%s"}}`,
+					ks.attribute_name, key_type_to_string(ks.key_type))
+			}
+			strings.write_string(&gsi_builder, `],"Projection":{{"ProjectionType":"`)
+			switch gsi.projection.projection_type {
+			case .ALL:       strings.write_string(&gsi_builder, "ALL")
+			case .KEYS_ONLY: strings.write_string(&gsi_builder, "KEYS_ONLY")
+			case .INCLUDE:   strings.write_string(&gsi_builder, "INCLUDE")
+			}
+			strings.write_string(&gsi_builder, `"`)
+			if nka, has_nka := gsi.projection.non_key_attributes.?; has_nka && len(nka) > 0 {
+				strings.write_string(&gsi_builder, `,"NonKeyAttributes":[`)
+				for attr, k in nka {
+					if k > 0 {
+						strings.write_string(&gsi_builder, ",")
+					}
+					fmt.sbprintf(&gsi_builder, `"%s"`, attr)
+				}
+				strings.write_string(&gsi_builder, "]")
+			}
+			strings.write_string(&gsi_builder, "}}")
+		}
+		strings.write_string(&gsi_builder, "]")
+
+		meta_item["GlobalSecondaryIndexes"] = String(strings.clone(strings.to_string(gsi_builder)))
+	}
+
 	// Encode to binary
 	return encode(meta_item)
 }
@@ -282,6 +339,17 @@ deserialize_table_metadata :: proc(data: []byte, allocator: mem.Allocator) -> (T
 		}
 	}
 
+	// Parse GlobalSecondaryIndexes from embedded JSON string
+	if gsi_val, gsi_found := meta_item["GlobalSecondaryIndexes"]; gsi_found {
+		#partial switch v in gsi_val {
+		case String:
+			gsis, gsi_ok := parse_gsis_json(string(v), allocator)
+			if gsi_ok && len(gsis) > 0 {
+				metadata.global_secondary_indexes = gsis
+			}
+		}
+	}
+
 	return metadata, true
 }
 
@@ -463,6 +531,7 @@ create_table :: proc(
 	table_name: string,
 	key_schema: []Key_Schema_Element,
 	attribute_definitions: []Attribute_Definition,
+	gsis: Maybe([]Global_Secondary_Index) = nil,
 ) -> (Table_Description, Storage_Error) {
 	table_lock := get_or_create_table_lock(engine, table_name)
 	sync.rw_mutex_lock(table_lock)
@@ -500,6 +569,34 @@ create_table :: proc(
 		ad.attribute_name = strings.clone(ad.attribute_name, engine.allocator)
 	}
 
+	// Deep copy GSI definitions into engine allocator
+	if gsi_defs, has_gsis := gsis.?; has_gsis && len(gsi_defs) > 0 {
+		owned_gsis := make([]Global_Secondary_Index, len(gsi_defs), engine.allocator)
+		for gsi_def, i in gsi_defs {
+			owned_gsis[i] = Global_Secondary_Index{
+				index_name = strings.clone(gsi_def.index_name, engine.allocator),
+				key_schema = make([]Key_Schema_Element, len(gsi_def.key_schema), engine.allocator),
+				projection = Projection{
+					projection_type = gsi_def.projection.projection_type,
+				},
+			}
+			for ks, j in gsi_def.key_schema {
+				owned_gsis[i].key_schema[j] = Key_Schema_Element{
+					attribute_name = strings.clone(ks.attribute_name, engine.allocator),
+					key_type = ks.key_type,
+				}
+			}
+			if nka, has_nka := gsi_def.projection.non_key_attributes.?; has_nka {
+				owned_nka := make([]string, len(nka), engine.allocator)
+				for attr, k in nka {
+					owned_nka[k] = strings.clone(attr, engine.allocator)
+				}
+				owned_gsis[i].projection.non_key_attributes = owned_nka
+			}
+		}
+		metadata.global_secondary_indexes = owned_gsis
+	}
+
 	// Serialize and store
 	meta_value, serialize_ok := serialize_table_metadata(&metadata)
 	if !serialize_ok {
@@ -522,6 +619,7 @@ create_table :: proc(
 		creation_date_time = now,
 		item_count = 0,
 		table_size_bytes = 0,
+		global_secondary_indexes = gsis,
 	}
 
 	return desc, .None
@@ -565,7 +663,6 @@ delete_table :: proc(engine: ^Storage_Engine, table_name: string) -> Storage_Err
 				break
 			}
 
-			// Delete this item
 			err: cstring
 			rocksdb.rocksdb_delete(
 				engine.db.handle,
@@ -582,6 +679,41 @@ delete_table :: proc(engine: ^Storage_Engine, table_name: string) -> Storage_Err
 		}
 	}
 
+	// Delete all GSI entries for this table
+	gsi_table_prefix := build_gsi_table_prefix(table_name)
+	defer delete(gsi_table_prefix)
+
+	gsi_iter := rocksdb.rocksdb_create_iterator(engine.db.handle, engine.db.read_options)
+	if gsi_iter != nil {
+		defer rocksdb.rocksdb_iter_destroy(gsi_iter)
+
+		rocksdb.rocksdb_iter_seek(gsi_iter, raw_data(gsi_table_prefix), c.size_t(len(gsi_table_prefix)))
+
+		for rocksdb.rocksdb_iter_valid(gsi_iter) != 0 {
+			key_len: c.size_t
+			key_ptr := rocksdb.rocksdb_iter_key(gsi_iter, &key_len)
+			key_bytes := key_ptr[:key_len]
+
+			if !has_prefix(key_bytes, gsi_table_prefix) {
+				break
+			}
+
+			err: cstring
+			rocksdb.rocksdb_delete(
+				engine.db.handle,
+				engine.db.write_options,
+				raw_data(key_bytes),
+				c.size_t(len(key_bytes)),
+				&err,
+			)
+			if err != nil {
+				rocksdb.rocksdb_free(rawptr(err))
+			}
+
+			rocksdb.rocksdb_iter_next(gsi_iter)
+		}
+	}
+
 	// Delete metadata
 	del_err := rocksdb.db_delete(&engine.db, meta_key)
 	if del_err != .None {
@@ -639,6 +771,17 @@ put_item :: proc(engine: ^Storage_Engine, table_name: string, item: Item) -> Sto
 	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
 	defer delete(storage_key)
 
+	// --- GSI cleanup: delete OLD GSI entries if item already exists ---
+	existing_value, existing_err := rocksdb.db_get(&engine.db, storage_key)
+	if existing_err == .None && existing_value != nil {
+		defer delete(existing_value)
+		old_item, decode_ok := decode(existing_value)
+		if decode_ok {
+			defer item_destroy(&old_item)
+			gsi_delete_entries(engine, table_name, old_item, &metadata)
+		}
+	}
+
 	// Encode item
 	encoded_item, encode_ok := encode(item)
 	if !encode_ok {
@@ -652,6 +795,12 @@ put_item :: proc(engine: ^Storage_Engine, table_name: string, item: Item) -> Sto
 		return .RocksDB_Error
 	}
 
+	// --- GSI maintenance: write NEW GSI entries ---
+	gsi_err := gsi_write_entries(engine, table_name, item, &metadata)
+	if gsi_err != .None {
+		return gsi_err
+	}
+
 	return .None
 }
 
@@ -748,6 +897,17 @@ delete_item :: proc(engine: ^Storage_Engine, table_name: string, key: Item) -> S
 	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
 	defer delete(storage_key)
 
+	// --- GSI cleanup: read existing item to know which GSI entries to remove ---
+	existing_value, existing_err := rocksdb.db_get(&engine.db, storage_key)
+	if existing_err == .None && existing_value != nil {
+		defer delete(existing_value)
+		old_item, decode_ok := decode(existing_value)
+		if decode_ok {
+			defer item_destroy(&old_item)
+			gsi_delete_entries(engine, table_name, old_item, &metadata)
+		}
+	}
+
 	// Delete from RocksDB
 	del_err := rocksdb.db_delete(&engine.db, storage_key)
 	if del_err != .None {

dynamodb/transact.odin

@@ -0,0 +1,719 @@
+// TransactWriteItems and TransactGetItems storage operations
+//
+// TransactWriteItems: Atomic write of up to 100 items across multiple tables.
+//   - Supports Put, Delete, Update, and ConditionCheck actions
+//   - ALL actions succeed or ALL fail (all-or-nothing)
+//   - ConditionExpressions are evaluated BEFORE any mutations
+//   - Uses exclusive locks on all involved tables
+//
+// TransactGetItems: Atomic read of up to 100 items across multiple tables.
+//   - Each item specifies TableName + Key + optional ProjectionExpression
+//   - All reads are consistent (snapshot isolation via table locks)
+package dynamodb
+
+import "core:strings"
+import "core:sync"
+import "../rocksdb"
+
+// ============================================================================
+// TransactWriteItems Types
+// ============================================================================
+
+Transact_Write_Action_Type :: enum {
+	Put,
+	Delete,
+	Update,
+	Condition_Check,
+}
+
+Transact_Write_Action :: struct {
+	type:                Transact_Write_Action_Type,
+	table_name:          string,
+	// For Put: the full item to write
+	item:                Maybe(Item),
+	// For Delete/Update/ConditionCheck: the key item
+	key:                 Maybe(Item),
+	// For Update: the parsed update plan
+	update_plan:         Maybe(Update_Plan),
+	// ConditionExpression components (shared across all action types)
+	condition_expr:      Maybe(string),
+	expr_attr_names:     Maybe(map[string]string),
+	expr_attr_values:    map[string]Attribute_Value,
+	// For Update: ReturnValuesOnConditionCheckFailure (not implemented yet, placeholder)
+}
+
+Transact_Write_Result :: struct {
+	// For now, either all succeed (no error) or we return a
+	// TransactionCanceledException with reasons per action.
+	cancellation_reasons: []Cancellation_Reason,
+}
+
+Cancellation_Reason :: struct {
+	code:    string, // "None", "ConditionalCheckFailed", "ValidationError", etc.
+	message: string,
+}
+
+transact_write_action_destroy :: proc(action: ^Transact_Write_Action) {
+	if item, has := action.item.?; has {
+		item_copy := item
+		item_destroy(&item_copy)
+	}
+	if key, has := action.key.?; has {
+		key_copy := key
+		item_destroy(&key_copy)
+	}
+	if plan, has := action.update_plan.?; has {
+		plan_copy := plan
+		update_plan_destroy(&plan_copy)
+	}
+	if names, has := action.expr_attr_names.?; has {
+		for k, v in names {
+			delete(k)
+			delete(v)
+		}
+		names_copy := names
+		delete(names_copy)
+	}
+	for k, v in action.expr_attr_values {
+		delete(k)
+		v_copy := v
+		attr_value_destroy(&v_copy)
+	}
+	delete(action.expr_attr_values)
+}
+
+transact_write_result_destroy :: proc(result: ^Transact_Write_Result) {
+	if result.cancellation_reasons != nil {
+		delete(result.cancellation_reasons)
+	}
+}
+
+// ============================================================================
+// TransactWriteItems — Execute an atomic batch of write operations
+//
+// DynamoDB semantics:
+//   1. Acquire exclusive locks on all involved tables
+//   2. Evaluate ALL ConditionExpressions (pre-flight check)
+//   3. If any condition fails → cancel entire transaction
+//   4. If all pass → apply all mutations
+//   5. Release locks
+//
+// Returns .None on success, Transaction_Cancelled on condition failure.
+// ============================================================================
+
+Transaction_Error :: enum {
+	None,
+	Cancelled,               // One or more conditions failed
+	Validation_Error,        // Bad request data
+	Internal_Error,          // Storage/serialization failure
+}
+
+transact_write_items :: proc(
+	engine: ^Storage_Engine,
+	actions: []Transact_Write_Action,
+) -> (Transact_Write_Result, Transaction_Error) {
+	result: Transact_Write_Result
+
+	if len(actions) == 0 {
+		return result, .Validation_Error
+	}
+
+	// ---- Step 1: Collect unique table names and acquire locks ----
+	table_set := make(map[string]bool, allocator = context.temp_allocator)
+	for action in actions {
+		table_set[action.table_name] = true
+	}
+
+	// Acquire exclusive locks on all tables in deterministic order
+	// to prevent deadlocks
+	table_names := make([dynamic]string, allocator = context.temp_allocator)
+	for name in table_set {
+		append(&table_names, name)
+	}
+	// Simple sort for deterministic lock ordering
+	for i := 0; i < len(table_names); i += 1 {
+		for j := i + 1; j < len(table_names); j += 1 {
+			if table_names[j] < table_names[i] {
+				table_names[i], table_names[j] = table_names[j], table_names[i]
+			}
+		}
+	}
+
+	locks := make([dynamic]^sync.RW_Mutex, allocator = context.temp_allocator)
+	for name in table_names {
+		lock := get_or_create_table_lock(engine, name)
+		sync.rw_mutex_lock(lock)
+		append(&locks, lock)
+	}
+	defer {
+		// Release all locks in reverse order
+		for i := len(locks) - 1; i >= 0; i -= 1 {
+			sync.rw_mutex_unlock(locks[i])
+		}
+	}
+
+	// ---- Step 2: Pre-flight — fetch metadata and existing items, evaluate conditions ----
+	reasons := make([]Cancellation_Reason, len(actions))
+	any_failed := false
+
+	// Cache table metadata to avoid redundant lookups
+	metadata_cache := make(map[string]Table_Metadata, allocator = context.temp_allocator)
+	defer {
+		for _, meta in metadata_cache {
+			meta_copy := meta
+			table_metadata_destroy(&meta_copy, engine.allocator)
+		}
+	}
+
+	for action, idx in actions {
+		// Get table metadata (cached)
+		metadata: ^Table_Metadata
+		if cached, found := &metadata_cache[action.table_name]; found {
+			metadata = cached
+		} else {
+			meta, meta_err := get_table_metadata(engine, action.table_name)
+			if meta_err != .None {
+				reasons[idx] = Cancellation_Reason{
+					code    = "ValidationError",
+					message = "Table not found",
+				}
+				any_failed = true
+				continue
+			}
+			metadata_cache[action.table_name] = meta
+			metadata = &metadata_cache[action.table_name]
+		}
+
+		// Determine the key item for this action
+		key_item: Item
+		switch action.type {
+		case .Put:
+			if item, has := action.item.?; has {
+				key_item = item // For Put, key is extracted from the item
+			} else {
+				reasons[idx] = Cancellation_Reason{
+					code    = "ValidationError",
+					message = "Put action missing Item",
+				}
+				any_failed = true
+				continue
+			}
+		case .Delete, .Update, .Condition_Check:
+			if key, has := action.key.?; has {
+				key_item = key
+			} else {
+				reasons[idx] = Cancellation_Reason{
+					code    = "ValidationError",
+					message = "Action missing Key",
+				}
+				any_failed = true
+				continue
+			}
+		}
+
+		// Evaluate ConditionExpression if present
+		if cond_str, has_cond := action.condition_expr.?; has_cond {
+			// Fetch existing item
+			existing_item, get_err := get_item_internal(engine, action.table_name, key_item, metadata)
+			if get_err != .None && get_err != .Item_Not_Found {
+				reasons[idx] = Cancellation_Reason{
+					code    = "InternalError",
+					message = "Failed to read existing item",
+				}
+				any_failed = true
+				continue
+			}
+			defer {
+				if ex, has_ex := existing_item.?; has_ex {
+					ex_copy := ex
+					item_destroy(&ex_copy)
+				}
+			}
+
+			// Parse and evaluate condition
+			filter_node, parse_ok := parse_filter_expression(
+				cond_str, action.expr_attr_names, action.expr_attr_values,
+			)
+			if !parse_ok || filter_node == nil {
+				reasons[idx] = Cancellation_Reason{
+					code    = "ValidationError",
+					message = "Invalid ConditionExpression",
+				}
+				any_failed = true
+				continue
+			}
+			defer {
+				filter_node_destroy(filter_node)
+				free(filter_node)
+			}
+
+			eval_item: Item
+			if item, has_item := existing_item.?; has_item {
+				eval_item = item
+			} else {
+				eval_item = Item{}
+			}
+
+			if !evaluate_filter(eval_item, filter_node) {
+				reasons[idx] = Cancellation_Reason{
+					code    = "ConditionalCheckFailed",
+					message = "The conditional request failed",
+				}
+				any_failed = true
+				continue
+			}
+		}
+
+		// ConditionCheck actions only validate — they don't mutate
+		if action.type == .Condition_Check {
+			reasons[idx] = Cancellation_Reason{code = "None"}
+			continue
+		}
+
+		// Validate key/item against schema
+		switch action.type {
+		case .Put:
+			if item, has := action.item.?; has {
+				validation_err := validate_item_key_types(
+					item, metadata.key_schema, metadata.attribute_definitions,
+				)
+				if validation_err != .None {
+					reasons[idx] = Cancellation_Reason{
+						code    = "ValidationError",
+						message = "Key attribute type mismatch",
+					}
+					any_failed = true
+					continue
+				}
+			}
+		case .Delete, .Update:
+			// Key validation happens during execution
+		case .Condition_Check:
+			// Already handled above
+		}
+
+		reasons[idx] = Cancellation_Reason{code = "None"}
+	}
+
+	// ---- Step 3: If any condition failed, return cancellation ----
+	if any_failed {
+		result.cancellation_reasons = reasons
+		return result, .Cancelled
+	}
+
+	// ---- Step 4: Apply all mutations ----
+	for &action, idx in actions {
+		metadata := &metadata_cache[action.table_name]
+
+		apply_err := transact_apply_action(engine, &action, metadata)
+		if apply_err != .None {
+			// This shouldn't happen after pre-validation, but handle gracefully
+			reasons[idx] = Cancellation_Reason{
+				code    = "InternalError",
+				message = "Failed to apply mutation",
+			}
+			// In a real impl we'd need to rollback. For now, report the failure.
+			result.cancellation_reasons = reasons
+			return result, .Internal_Error
+		}
+	}
+
+	delete(reasons)
+	return result, .None
+}
+
+// Apply a single transact write action (called after all conditions have passed)
+@(private = "file")
+transact_apply_action :: proc(
+	engine: ^Storage_Engine,
+	action: ^Transact_Write_Action,
+	metadata: ^Table_Metadata,
+) -> Storage_Error {
+	switch action.type {
+	case .Put:
+		if item, has := action.item.?; has {
+			return put_item_internal(engine, action.table_name, item, metadata)
+		}
+		return .Invalid_Key
+
+	case .Delete:
+		if key, has := action.key.?; has {
+			return delete_item_internal(engine, action.table_name, key, metadata)
+		}
+		return .Invalid_Key
+
+	case .Update:
+		if key, has := action.key.?; has {
+			if plan, has_plan := action.update_plan.?; has_plan {
+				plan_copy := plan
+				_, _, err := update_item_internal(engine, action.table_name, key, &plan_copy, metadata)
+				return err
+			}
+			return .Invalid_Key
+		}
+		return .Invalid_Key
+
+	case .Condition_Check:
+		return .None // No mutation
+	}
+	return .None
+}
+
+// ============================================================================
+// Internal storage operations that skip lock acquisition
+// (Used by transact_write_items which manages its own locking)
+// ============================================================================
+
+get_item_internal :: proc(
+	engine: ^Storage_Engine,
+	table_name: string,
+	key: Item,
+	metadata: ^Table_Metadata,
+) -> (Maybe(Item), Storage_Error) {
+	key_struct, key_ok := key_from_item(key, metadata.key_schema)
+	if !key_ok {
+		return nil, .Missing_Key_Attribute
+	}
+	defer key_destroy(&key_struct)
+
+	key_values, kv_ok := key_get_values(&key_struct)
+	if !kv_ok {
+		return nil, .Invalid_Key
+	}
+
+	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
+	defer delete(storage_key)
+
+	value, get_err := rocksdb.db_get(&engine.db, storage_key)
+	if get_err == .NotFound {
+		return nil, .None
+	}
+	if get_err != .None {
+		return nil, .RocksDB_Error
+	}
+	defer delete(value)
+
+	item, decode_ok := decode(value)
+	if !decode_ok {
+		return nil, .Serialization_Error
+	}
+
+	return item, .None
+}
+
+put_item_internal :: proc(
+	engine: ^Storage_Engine,
+	table_name: string,
+	item: Item,
+	metadata: ^Table_Metadata,
+) -> Storage_Error {
+	key_struct, key_ok := key_from_item(item, metadata.key_schema)
+	if !key_ok {
+		return .Missing_Key_Attribute
+	}
+	defer key_destroy(&key_struct)
+
+	key_values, kv_ok := key_get_values(&key_struct)
+	if !kv_ok {
+		return .Invalid_Key
+	}
+
+	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
+	defer delete(storage_key)
+
+	encoded_item, encode_ok := encode(item)
+	if !encode_ok {
+		return .Serialization_Error
+	}
+	defer delete(encoded_item)
+
+	put_err := rocksdb.db_put(&engine.db, storage_key, encoded_item)
+	if put_err != .None {
+		return .RocksDB_Error
+	}
+
+	return .None
+}
+
+delete_item_internal :: proc(
+	engine: ^Storage_Engine,
+	table_name: string,
+	key: Item,
+	metadata: ^Table_Metadata,
+) -> Storage_Error {
+	key_struct, key_ok := key_from_item(key, metadata.key_schema)
+	if !key_ok {
+		return .Missing_Key_Attribute
+	}
+	defer key_destroy(&key_struct)
+
+	key_values, kv_ok := key_get_values(&key_struct)
+	if !kv_ok {
+		return .Invalid_Key
+	}
+
+	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
+	defer delete(storage_key)
+
+	del_err := rocksdb.db_delete(&engine.db, storage_key)
+	if del_err != .None {
+		return .RocksDB_Error
+	}
+
+	return .None
+}
+
+update_item_internal :: proc(
+	engine: ^Storage_Engine,
+	table_name: string,
+	key_item: Item,
+	plan: ^Update_Plan,
+	metadata: ^Table_Metadata,
+) -> (old_item: Maybe(Item), new_item: Maybe(Item), err: Storage_Error) {
+	key_struct, key_ok := key_from_item(key_item, metadata.key_schema)
+	if !key_ok {
+		return nil, nil, .Missing_Key_Attribute
+	}
+	defer key_destroy(&key_struct)
+
+	key_values, kv_ok := key_get_values(&key_struct)
+	if !kv_ok {
+		return nil, nil, .Invalid_Key
+	}
+
+	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
+	defer delete(storage_key)
+
+	// Fetch existing item
+	existing_encoded, get_err := rocksdb.db_get(&engine.db, storage_key)
+	existing_item: Item
+
+	if get_err == .None && existing_encoded != nil {
+		defer delete(existing_encoded)
+		decoded, decode_ok := decode(existing_encoded)
+		if !decode_ok {
+			return nil, nil, .Serialization_Error
+		}
+		existing_item = decoded
+		old_item = item_deep_copy(existing_item)
+	} else if get_err == .NotFound || existing_encoded == nil {
+		existing_item = make(Item)
+		for ks in metadata.key_schema {
+			if val, found := key_item[ks.attribute_name]; found {
+				existing_item[strings.clone(ks.attribute_name)] = attr_value_deep_copy(val)
+			}
+		}
+	} else {
+		return nil, nil, .RocksDB_Error
+	}
+
+	if !execute_update_plan(&existing_item, plan) {
+		item_destroy(&existing_item)
+		if old, has := old_item.?; has {
+			old_copy := old
+			item_destroy(&old_copy)
+		}
+		return nil, nil, .Invalid_Key
+	}
+
+	encoded_item, encode_ok := encode(existing_item)
+	if !encode_ok {
+		item_destroy(&existing_item)
+		if old, has := old_item.?; has {
+			old_copy := old
+			item_destroy(&old_copy)
+		}
+		return nil, nil, .Serialization_Error
+	}
+	defer delete(encoded_item)
+
+	put_err := rocksdb.db_put(&engine.db, storage_key, encoded_item)
+	if put_err != .None {
+		item_destroy(&existing_item)
+		if old, has := old_item.?; has {
+			old_copy := old
+			item_destroy(&old_copy)
+		}
+		return nil, nil, .RocksDB_Error
+	}
+
+	new_item = existing_item
+	return old_item, new_item, .None
+}
+
+// ============================================================================
+// TransactGetItems Types
+// ============================================================================
+
+Transact_Get_Action :: struct {
+	table_name: string,
+	key:        Item,
+	projection: Maybe([]string),  // Optional ProjectionExpression paths
+}
+
+Transact_Get_Result :: struct {
+	items: []Maybe(Item),  // One per action, nil if item not found
+}
+
+transact_get_action_destroy :: proc(action: ^Transact_Get_Action) {
+	item_destroy(&action.key)
+	if proj, has := action.projection.?; has {
+		delete(proj)
+	}
+}
+
+transact_get_result_destroy :: proc(result: ^Transact_Get_Result) {
+	for &maybe_item in result.items {
+		if item, has := maybe_item.?; has {
+			item_copy := item
+			item_destroy(&item_copy)
+		}
+	}
+	delete(result.items)
+}
+
+// ============================================================================
+// TransactGetItems — Atomically read up to 100 items
+//
+// DynamoDB semantics:
+//   - All reads are performed with a consistent snapshot
+//   - Missing items are returned as nil (no error)
+//   - ProjectionExpression is applied per-item
+// ============================================================================
+
+transact_get_items :: proc(
+	engine: ^Storage_Engine,
+	actions: []Transact_Get_Action,
+) -> (Transact_Get_Result, Transaction_Error) {
+	result: Transact_Get_Result
+
+	if len(actions) == 0 {
+		return result, .Validation_Error
+	}
+
+	// Collect unique tables and acquire shared locks in deterministic order
+	table_set := make(map[string]bool, allocator = context.temp_allocator)
+	for action in actions {
+		table_set[action.table_name] = true
+	}
+
+	table_names := make([dynamic]string, allocator = context.temp_allocator)
+	for name in table_set {
+		append(&table_names, name)
+	}
+	for i := 0; i < len(table_names); i += 1 {
+		for j := i + 1; j < len(table_names); j += 1 {
+			if table_names[j] < table_names[i] {
+				table_names[i], table_names[j] = table_names[j], table_names[i]
+			}
+		}
+	}
+
+	locks := make([dynamic]^sync.RW_Mutex, allocator = context.temp_allocator)
+	for name in table_names {
+		lock := get_or_create_table_lock(engine, name)
+		sync.rw_mutex_shared_lock(lock)
+		append(&locks, lock)
+	}
+	defer {
+		for i := len(locks) - 1; i >= 0; i -= 1 {
+			sync.rw_mutex_shared_unlock(locks[i])
+		}
+	}
+
+	// Cache metadata
+	metadata_cache := make(map[string]Table_Metadata, allocator = context.temp_allocator)
+	defer {
+		for _, meta in metadata_cache {
+			meta_copy := meta
+			table_metadata_destroy(&meta_copy, engine.allocator)
+		}
+	}
+
+	items := make([]Maybe(Item), len(actions))
+
+	for action, idx in actions {
+		// Get metadata (cached)
+		metadata: ^Table_Metadata
+		if cached, found := &metadata_cache[action.table_name]; found {
+			metadata = cached
+		} else {
+			meta, meta_err := get_table_metadata(engine, action.table_name)
+			if meta_err != .None {
+				items[idx] = nil
+				continue
+			}
+			metadata_cache[action.table_name] = meta
+			metadata = &metadata_cache[action.table_name]
+		}
+
+		// Fetch item
+		item_result, get_err := get_item_internal(engine, action.table_name, action.key, metadata)
+		if get_err != .None {
+			items[idx] = nil
+			continue
+		}
+
+		// Apply projection if specified
+		if item, has_item := item_result.?; has_item {
+			if proj, has_proj := action.projection.?; has_proj && len(proj) > 0 {
+				projected := apply_projection(item, proj)
+				item_copy := item
+				item_destroy(&item_copy)
+				items[idx] = projected
+			} else {
+				items[idx] = item
+			}
+		} else {
+			items[idx] = nil
+		}
+	}
+
+	result.items = items
+	return result, .None
+}
+
+// ============================================================================
+// Helper: Extract modified attribute paths from an Update_Plan
+//
+// Used for UPDATED_NEW / UPDATED_OLD ReturnValues filtering.
+// DynamoDB only returns the attributes that were actually modified
+// by the UpdateExpression, not the entire item.
+// ============================================================================
+
+get_update_plan_modified_paths :: proc(plan: ^Update_Plan) -> []string {
+	paths := make(map[string]bool, allocator = context.temp_allocator)
+
+	for action in plan.sets {
+		paths[action.path] = true
+	}
+	for action in plan.removes {
+		paths[action.path] = true
+	}
+	for action in plan.adds {
+		paths[action.path] = true
+	}
+	for action in plan.deletes {
+		paths[action.path] = true
+	}
+
+	result := make([]string, len(paths))
+	i := 0
+	for path in paths {
+		result[i] = path
+		i += 1
+	}
+	return result
+}
+
+// Filter an item to only include the specified attribute paths.
+// Returns a new deep-copied item containing only matching attributes.
+filter_item_to_paths :: proc(item: Item, paths: []string) -> Item {
+	result := make(Item)
+	for path in paths {
+		if val, found := item[path]; found {
+			result[strings.clone(path)] = attr_value_deep_copy(val)
+		}
+	}
+	return result
+}

dynamodb/update_item.odin

@@ -120,6 +120,12 @@ update_item :: proc(
 		return nil, nil, .RocksDB_Error
 	}
 
+	// --- GSI maintenance: delete old entries, write new entries ---
+	if old, has := old_item.?; has {
+		gsi_delete_entries(engine, table_name, old, &metadata)
+	}
+	gsi_write_entries(engine, table_name, existing_item, &metadata)
+
 	new_item = existing_item
 	return old_item, new_item, .None
 }

gsi_handlers.odin

@@ -0,0 +1,276 @@
+// gsi_handlers.odin — GSI-related HTTP handler helpers
+//
+// This file lives in the main package alongside main.odin.
+// It provides:
+//   1. parse_global_secondary_indexes — parse GSI definitions from CreateTable request
+//   2. parse_index_name              — extract IndexName from Query/Scan requests
+//   3. Projection type helper for response building
+package main
+
+import "core:encoding/json"
+import "core:strings"
+import "dynamodb"
+
+// ============================================================================
+// Parse GlobalSecondaryIndexes from CreateTable request body
+//
+// DynamoDB CreateTable request format for GSIs:
+// {
+//   "GlobalSecondaryIndexes": [
+//     {
+//       "IndexName": "email-index",
+//       "KeySchema": [
+//         { "AttributeName": "email", "KeyType": "HASH" },
+//         { "AttributeName": "timestamp", "KeyType": "RANGE" }
+//       ],
+//       "Projection": {
+//         "ProjectionType": "ALL" | "KEYS_ONLY" | "INCLUDE",
+//         "NonKeyAttributes": ["attr1", "attr2"]  // only for INCLUDE
+//       }
+//     }
+//   ]
+// }
+//
+// Returns nil if no GSI definitions are present (valid — GSIs are optional).
+// ============================================================================
+
+parse_global_secondary_indexes :: proc(
+	root: json.Object,
+	attr_defs: []dynamodb.Attribute_Definition,
+) -> Maybe([]dynamodb.Global_Secondary_Index) {
+	gsi_val, found := root["GlobalSecondaryIndexes"]
+	if !found {
+		return nil
+	}
+
+	gsi_arr, ok := gsi_val.(json.Array)
+	if !ok || len(gsi_arr) == 0 {
+		return nil
+	}
+
+	gsis := make([]dynamodb.Global_Secondary_Index, len(gsi_arr))
+
+	for elem, i in gsi_arr {
+		elem_obj, elem_ok := elem.(json.Object)
+		if !elem_ok {
+			cleanup_parsed_gsis(gsis[:i])
+			delete(gsis)
+			return nil
+		}
+
+		gsi, gsi_ok := parse_single_gsi(elem_obj, attr_defs)
+		if !gsi_ok {
+			cleanup_parsed_gsis(gsis[:i])
+			delete(gsis)
+			return nil
+		}
+
+		gsis[i] = gsi
+	}
+
+	return gsis
+}
+
+@(private = "file")
+parse_single_gsi :: proc(
+	obj: json.Object,
+	attr_defs: []dynamodb.Attribute_Definition,
+) -> (dynamodb.Global_Secondary_Index, bool) {
+	gsi: dynamodb.Global_Secondary_Index
+
+	// IndexName (required)
+	idx_val, idx_found := obj["IndexName"]
+	if !idx_found {
+		return {}, false
+	}
+	idx_str, idx_ok := idx_val.(json.String)
+	if !idx_ok {
+		return {}, false
+	}
+	gsi.index_name = strings.clone(string(idx_str))
+
+	// KeySchema (required)
+	ks_val, ks_found := obj["KeySchema"]
+	if !ks_found {
+		delete(gsi.index_name)
+		return {}, false
+	}
+	ks_arr, ks_ok := ks_val.(json.Array)
+	if !ks_ok || len(ks_arr) == 0 || len(ks_arr) > 2 {
+		delete(gsi.index_name)
+		return {}, false
+	}
+
+	key_schema := make([]dynamodb.Key_Schema_Element, len(ks_arr))
+	hash_count := 0
+
+	for ks_elem, j in ks_arr {
+		ks_obj, kobj_ok := ks_elem.(json.Object)
+		if !kobj_ok {
+			for k in 0..<j { delete(key_schema[k].attribute_name) }
+			delete(key_schema)
+			delete(gsi.index_name)
+			return {}, false
+		}
+
+		an_val, an_found := ks_obj["AttributeName"]
+		if !an_found {
+			for k in 0..<j { delete(key_schema[k].attribute_name) }
+			delete(key_schema)
+			delete(gsi.index_name)
+			return {}, false
+		}
+		an_str, an_ok := an_val.(json.String)
+		if !an_ok {
+			for k in 0..<j { delete(key_schema[k].attribute_name) }
+			delete(key_schema)
+			delete(gsi.index_name)
+			return {}, false
+		}
+
+		kt_val, kt_found := ks_obj["KeyType"]
+		if !kt_found {
+			for k in 0..<j { delete(key_schema[k].attribute_name) }
+			delete(key_schema)
+			delete(gsi.index_name)
+			return {}, false
+		}
+		kt_str, kt_ok := kt_val.(json.String)
+		if !kt_ok {
+			for k in 0..<j { delete(key_schema[k].attribute_name) }
+			delete(key_schema)
+			delete(gsi.index_name)
+			return {}, false
+		}
+
+		kt, kt_parse_ok := dynamodb.key_type_from_string(string(kt_str))
+		if !kt_parse_ok {
+			for k in 0..<j { delete(key_schema[k].attribute_name) }
+			delete(key_schema)
+			delete(gsi.index_name)
+			return {}, false
+		}
+
+		if kt == .HASH {
+			hash_count += 1
+		}
+
+		// Validate that the GSI key attribute is in AttributeDefinitions
+		attr_defined := false
+		for ad in attr_defs {
+			if ad.attribute_name == string(an_str) {
+				attr_defined = true
+				break
+			}
+		}
+		if !attr_defined {
+			for k in 0..<j { delete(key_schema[k].attribute_name) }
+			delete(key_schema)
+			delete(gsi.index_name)
+			return {}, false
+		}
+
+		key_schema[j] = dynamodb.Key_Schema_Element{
+			attribute_name = strings.clone(string(an_str)),
+			key_type = kt,
+		}
+	}
+
+	// Must have exactly one HASH key
+	if hash_count != 1 {
+		for ks in key_schema { delete(ks.attribute_name) }
+		delete(key_schema)
+		delete(gsi.index_name)
+		return {}, false
+	}
+
+	gsi.key_schema = key_schema
+
+	// Projection (optional — defaults to ALL)
+	gsi.projection.projection_type = .ALL
+	if proj_val, proj_found := obj["Projection"]; proj_found {
+		if proj_obj, proj_ok := proj_val.(json.Object); proj_ok {
+			if pt_val, pt_found := proj_obj["ProjectionType"]; pt_found {
+				if pt_str, pt_ok := pt_val.(json.String); pt_ok {
+					switch string(pt_str) {
+					case "ALL":       gsi.projection.projection_type = .ALL
+					case "KEYS_ONLY": gsi.projection.projection_type = .KEYS_ONLY
+					case "INCLUDE":   gsi.projection.projection_type = .INCLUDE
+					}
+				}
+			}
+
+			// NonKeyAttributes (only valid for INCLUDE projection)
+			if nka_val, nka_found := proj_obj["NonKeyAttributes"]; nka_found {
+				if nka_arr, nka_ok := nka_val.(json.Array); nka_ok && len(nka_arr) > 0 {
+					nka := make([]string, len(nka_arr))
+					for attr_val, k in nka_arr {
+						if attr_str, attr_ok := attr_val.(json.String); attr_ok {
+							nka[k] = strings.clone(string(attr_str))
+						}
+					}
+					gsi.projection.non_key_attributes = nka
+				}
+			}
+		}
+	}
+
+	return gsi, true
+}
+
+@(private = "file")
+cleanup_parsed_gsis :: proc(gsis: []dynamodb.Global_Secondary_Index) {
+	for gsi in gsis {
+		delete(gsi.index_name)
+		for ks in gsi.key_schema {
+			delete(ks.attribute_name)
+		}
+		delete(gsi.key_schema)
+		if nka, has_nka := gsi.projection.non_key_attributes.?; has_nka {
+			for attr in nka { delete(attr) }
+			delete(nka)
+		}
+	}
+}
+
+// ============================================================================
+// Parse IndexName from Query/Scan request
+// ============================================================================
+
+parse_index_name :: proc(request_body: []byte) -> Maybe(string) {
+	data, parse_err := json.parse(request_body, allocator = context.temp_allocator)
+	if parse_err != nil {
+		return nil
+	}
+	defer json.destroy_value(data)
+
+	root, root_ok := data.(json.Object)
+	if !root_ok {
+		return nil
+	}
+
+	idx_val, found := root["IndexName"]
+	if !found {
+		return nil
+	}
+
+	idx_str, ok := idx_val.(json.String)
+	if !ok {
+		return nil
+	}
+
+	return string(idx_str)
+}
+
+// ============================================================================
+// Projection type to string for DescribeTable response
+// ============================================================================
+
+projection_type_to_string :: proc(pt: dynamodb.Projection_Type) -> string {
+	switch pt {
+	case .ALL:       return "ALL"
+	case .KEYS_ONLY: return "KEYS_ONLY"
+	case .INCLUDE:   return "INCLUDE"
+	}
+	return "ALL"
+}

main.odin

@@ -106,6 +106,10 @@ handle_dynamodb_request :: proc(ctx: rawptr, request: ^HTTP_Request, request_all
 		handle_batch_write_item(engine, request, &response)
 	case .BatchGetItem:
 		handle_batch_get_item(engine, request, &response)
+	case .TransactWriteItems:
+		handle_transact_write_items(engine, request, &response)
+	case .TransactGetItems:
+		handle_transact_get_items(engine, request, &response)
 	case .Unknown:
 		return make_error_response(&response, .ValidationException, "Unknown operation")
 	case:
@@ -169,8 +173,25 @@ handle_create_table :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Req
 		return
 	}
 
+	// Parse GlobalSecondaryIndexes (optional)
+	gsis := parse_global_secondary_indexes(root, attr_defs)
+	defer {
+		if gsi_list, has := gsis.?; has {
+			for &g in gsi_list {
+				delete(g.index_name)
+				for &ks in g.key_schema { delete(ks.attribute_name) }
+				delete(g.key_schema)
+				if nka, has_nka := g.projection.non_key_attributes.?; has_nka {
+					for a in nka { delete(a) }
+					delete(nka)
+				}
+			}
+			delete(gsi_list)
+		}
+	}
+
 	// Create the table
-	desc, create_err := dynamodb.create_table(engine, string(table_name), key_schema, attr_defs)
+	desc, create_err := dynamodb.create_table(engine, string(table_name), key_schema, attr_defs, gsis)
 	if create_err != .None {
 		#partial switch create_err {
 		case .Table_Already_Exists:
@@ -257,7 +278,30 @@ handle_describe_table :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_R
 			ad.attribute_name, dynamodb.scalar_type_to_string(ad.attribute_type))
 	}
 
-	strings.write_string(&builder, `]}}`)
+	strings.write_string(&builder, `]`)
+
+	// Include GSI Info — INSIDE the Table object, before the closing braces
+	if gsis, has_gsis := metadata.global_secondary_indexes.?; has_gsis && len(gsis) > 0 {
+		strings.write_string(&builder, `,"GlobalSecondaryIndexes":[`)
+		for gsi, gi in gsis {
+			if gi > 0 do strings.write_string(&builder, ",")
+			strings.write_string(&builder, `{"IndexName":"`)
+			strings.write_string(&builder, gsi.index_name)
+			strings.write_string(&builder, `","KeySchema":[`)
+			for ks, ki in gsi.key_schema {
+				if ki > 0 do strings.write_string(&builder, ",")
+				fmt.sbprintf(&builder, `{"AttributeName":"%s","KeyType":"%s"}`,
+					ks.attribute_name, dynamodb.key_type_to_string(ks.key_type))
+			}
+			strings.write_string(&builder, `],"Projection":{"ProjectionType":"`)
+			strings.write_string(&builder, projection_type_to_string(gsi.projection.projection_type))
+			strings.write_string(&builder, `"},"IndexStatus":"ACTIVE"}`)
+		}
+		strings.write_string(&builder, "]")
+	}
+
+	// Close Table object and root object
+	strings.write_string(&builder, `}}`)
 
 	resp_body := strings.to_string(builder)
 	response_set_body(response, transmute([]byte)resp_body)
@@ -657,7 +701,9 @@ handle_update_item :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Requ
 
 	case "UPDATED_NEW":
 		if new_val, has := new_item.?; has {
-			item_json := dynamodb.serialize_item(new_val)
+			filtered := filter_updated_attributes(new_val, &plan)
+			defer dynamodb.item_destroy(&filtered)
+			item_json := dynamodb.serialize_item(filtered)
 			resp := fmt.aprintf(`{"Attributes":%s}`, item_json)
 			response_set_body(response, transmute([]byte)resp)
 		} else {
@@ -666,7 +712,9 @@ handle_update_item :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Requ
 
 	case "UPDATED_OLD":
 		if old, has := old_item.?; has {
-			item_json := dynamodb.serialize_item(old)
+			filtered := filter_updated_attributes(old, &plan)
+			defer dynamodb.item_destroy(&filtered)
+			item_json := dynamodb.serialize_item(filtered)
 			resp := fmt.aprintf(`{"Attributes":%s}`, item_json)
 			response_set_body(response, transmute([]byte)resp)
 		} else {
@@ -1046,6 +1094,9 @@ handle_query :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Request, r
 		return
 	}
 
+	// Grab index name from request body
+	index_name := parse_index_name(request.body)
+
 	// Fetch table metadata early for ExclusiveStartKey parsing
 	metadata, meta_err := dynamodb.get_table_metadata(engine, table_name)
 	if meta_err != .None {
@@ -1073,6 +1124,8 @@ handle_query :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Request, r
 	copy(pk_owned, pk_bytes)
 	defer delete(pk_owned)
 
+	// ---- Parse shared parameters BEFORE the GSI/table branch ----
+
 	// Parse Limit
 	limit := dynamodb.parse_limit(request.body)
 	if limit == 0 {
@@ -1099,13 +1152,6 @@ handle_query :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Request, r
 		sk_condition = skc
 	}
 
-	result, err := dynamodb.query(engine, table_name, pk_owned, exclusive_start_key, limit, sk_condition)
-	if err != .None {
-		handle_storage_error(response, err)
-		return
-	}
-	defer dynamodb.query_result_destroy(&result)
-
 	// ---- Parse ExpressionAttributeNames/Values for filter/projection ----
 	attr_names := dynamodb.parse_expression_attribute_names(request.body)
 	defer {
@@ -1129,6 +1175,62 @@ handle_query :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Request, r
 		delete(attr_values)
 	}
 
+	// ---- GSI query path ----
+	if idx_name, has_idx := index_name.?; has_idx {
+		_, gsi_found := dynamodb.find_gsi(&metadata, idx_name)
+		if !gsi_found {
+			make_error_response(response, .ValidationException,
+				fmt.tprintf("The table does not have the specified index: %s", idx_name))
+			return
+		}
+
+		result, err := dynamodb.gsi_query(engine, table_name, idx_name,
+			pk_owned, exclusive_start_key, limit, sk_condition)
+		if err != .None {
+			handle_storage_error(response, err)
+			return
+		}
+		defer dynamodb.query_result_destroy(&result)
+
+		// Apply FilterExpression
+		filtered_items := apply_filter_to_items(request.body, result.items, attr_names, attr_values)
+		scanned_count := len(result.items)
+
+		// Apply ProjectionExpression
+		projection, has_proj := dynamodb.parse_projection_expression(request.body, attr_names)
+		final_items: []dynamodb.Item
+
+		if has_proj && len(projection) > 0 {
+			projected := make([]dynamodb.Item, len(filtered_items))
+			for item, i in filtered_items {
+				projected[i] = dynamodb.apply_projection(item, projection)
+			}
+			final_items = projected
+		} else {
+			final_items = filtered_items
+		}
+
+		write_items_response_with_pagination_ex(
+			response, final_items, result.last_evaluated_key, &metadata, scanned_count,
+		)
+
+		if has_proj && len(projection) > 0 {
+			for &item in final_items {
+				dynamodb.item_destroy(&item)
+			}
+			delete(final_items)
+		}
+		return
+	}
+
+	// ---- Main table query path ----
+	result, err := dynamodb.query(engine, table_name, pk_owned, exclusive_start_key, limit, sk_condition)
+	if err != .None {
+		handle_storage_error(response, err)
+		return
+	}
+	defer dynamodb.query_result_destroy(&result)
+
 	// ---- Apply FilterExpression (post-query filter) ----
 	filtered_items := apply_filter_to_items(request.body, result.items, attr_names, attr_values)
 	scanned_count := len(result.items)
@@ -1169,6 +1271,9 @@ handle_scan :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Request, re
 		return
 	}
 
+	// Grab index name from request body
+	index_name := parse_index_name(request.body)
+
 	metadata, meta_err := dynamodb.get_table_metadata(engine, table_name)
 	if meta_err != .None {
 		handle_storage_error(response, meta_err)
@@ -1194,13 +1299,6 @@ handle_scan :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Request, re
 		}
 	}
 
-	result, err := dynamodb.scan(engine, table_name, exclusive_start_key, limit)
-	if err != .None {
-		handle_storage_error(response, err)
-		return
-	}
-	defer dynamodb.scan_result_destroy(&result)
-
 	// ---- Parse ExpressionAttributeNames/Values for filter/projection ----
 	attr_names := dynamodb.parse_expression_attribute_names(request.body)
 	defer {
@@ -1224,6 +1322,59 @@ handle_scan :: proc(engine: ^dynamodb.Storage_Engine, request: ^HTTP_Request, re
 		delete(attr_values)
 	}
 
+	// ---- GSI scan path ----
+	if idx_name, has_idx := index_name.?; has_idx {
+		_, gsi_found := dynamodb.find_gsi(&metadata, idx_name)
+		if !gsi_found {
+			make_error_response(response, .ValidationException,
+				fmt.tprintf("The table does not have the specified index: %s", idx_name))
+			return
+		}
+
+		result, err := dynamodb.gsi_scan(engine, table_name, idx_name, exclusive_start_key, limit)
+		if err != .None {
+			handle_storage_error(response, err)
+			return
+		}
+		defer dynamodb.scan_result_destroy(&result)
+
+		filtered_items := apply_filter_to_items(request.body, result.items, attr_names, attr_values)
+		scanned_count := len(result.items)
+
+		projection, has_proj := dynamodb.parse_projection_expression(request.body, attr_names)
+		final_items: []dynamodb.Item
+
+		if has_proj && len(projection) > 0 {
+			projected := make([]dynamodb.Item, len(filtered_items))
+			for item, i in filtered_items {
+				projected[i] = dynamodb.apply_projection(item, projection)
+			}
+			final_items = projected
+		} else {
+			final_items = filtered_items
+		}
+
+		write_items_response_with_pagination_ex(
+			response, final_items, result.last_evaluated_key, &metadata, scanned_count,
+		)
+
+		if has_proj && len(projection) > 0 {
+			for &item in final_items {
+				dynamodb.item_destroy(&item)
+			}
+			delete(final_items)
+		}
+		return
+	}
+
+	// ---- Main table scan path ----
+	result, err := dynamodb.scan(engine, table_name, exclusive_start_key, limit)
+	if err != .None {
+		handle_storage_error(response, err)
+		return
+	}
+	defer dynamodb.scan_result_destroy(&result)
+
 	// ---- Apply FilterExpression ----
 	filtered_items := apply_filter_to_items(request.body, result.items, attr_names, attr_values)
 	scanned_count := len(result.items)

transact_handlers.odin

@@ -0,0 +1,595 @@
+// transact_handlers.odin — HTTP handlers for TransactWriteItems and TransactGetItems
+//
+// Also contains the UPDATED_NEW / UPDATED_OLD filtering helper for UpdateItem.
+package main
+
+import "core:encoding/json"
+import "core:fmt"
+import "core:strings"
+import "dynamodb"
+
+// ============================================================================
+// TransactWriteItems Handler
+//
+// Request format:
+// {
+//   "TransactItems": [
+//     {
+//       "Put": {
+//         "TableName": "...",
+//         "Item": { ... },
+//         "ConditionExpression": "...",          // optional
+//         "ExpressionAttributeNames": { ... },   // optional
+//         "ExpressionAttributeValues": { ... }    // optional
+//       }
+//     },
+//     {
+//       "Delete": {
+//         "TableName": "...",
+//         "Key": { ... },
+//         "ConditionExpression": "...",           // optional
+//         ...
+//       }
+//     },
+//     {
+//       "Update": {
+//         "TableName": "...",
+//         "Key": { ... },
+//         "UpdateExpression": "...",
+//         "ConditionExpression": "...",           // optional
+//         "ExpressionAttributeNames": { ... },   // optional
+//         "ExpressionAttributeValues": { ... }    // optional
+//       }
+//     },
+//     {
+//       "ConditionCheck": {
+//         "TableName": "...",
+//         "Key": { ... },
+//         "ConditionExpression": "...",
+//         "ExpressionAttributeNames": { ... },   // optional
+//         "ExpressionAttributeValues": { ... }    // optional
+//       }
+//     }
+//   ]
+// }
+// ============================================================================
+
+handle_transact_write_items :: proc(
+	engine: ^dynamodb.Storage_Engine,
+	request: ^HTTP_Request,
+	response: ^HTTP_Response,
+) {
+	data, parse_err := json.parse(request.body, allocator = context.allocator)
+	if parse_err != nil {
+		make_error_response(response, .SerializationException, "Invalid JSON")
+		return
+	}
+	defer json.destroy_value(data)
+
+	root, root_ok := data.(json.Object)
+	if !root_ok {
+		make_error_response(response, .SerializationException, "Request must be an object")
+		return
+	}
+
+	transact_items_val, found := root["TransactItems"]
+	if !found {
+		make_error_response(response, .ValidationException, "Missing TransactItems")
+		return
+	}
+
+	transact_items, ti_ok := transact_items_val.(json.Array)
+	if !ti_ok {
+		make_error_response(response, .ValidationException, "TransactItems must be an array")
+		return
+	}
+
+	if len(transact_items) == 0 {
+		make_error_response(response, .ValidationException,
+			"TransactItems must contain at least one item")
+		return
+	}
+
+	if len(transact_items) > 100 {
+		make_error_response(response, .ValidationException,
+			"Member must have length less than or equal to 100")
+		return
+	}
+
+	// Parse each action
+	actions := make([dynamic]dynamodb.Transact_Write_Action)
+	defer {
+		for &action in actions {
+			dynamodb.transact_write_action_destroy(&action)
+		}
+		delete(actions)
+	}
+
+	for elem in transact_items {
+		elem_obj, elem_ok := elem.(json.Object)
+		if !elem_ok {
+			make_error_response(response, .ValidationException,
+				"Each TransactItem must be an object")
+			return
+		}
+
+		action, action_ok := parse_transact_write_action(elem_obj)
+		if !action_ok {
+			make_error_response(response, .ValidationException,
+				"Invalid TransactItem action")
+			return
+		}
+		append(&actions, action)
+	}
+
+	// Execute transaction
+	result, tx_err := dynamodb.transact_write_items(engine, actions[:])
+	defer dynamodb.transact_write_result_destroy(&result)
+
+	switch tx_err {
+	case .None:
+		response_set_body(response, transmute([]byte)string("{}"))
+
+	case .Cancelled:
+		// Build TransactionCanceledException response
+		builder := strings.builder_make()
+		strings.write_string(&builder, `{"__type":"com.amazonaws.dynamodb.v20120810#TransactionCanceledException","message":"Transaction cancelled, please refer cancellation reasons for specific reasons [`)
+
+		for reason, i in result.cancellation_reasons {
+			if i > 0 {
+				strings.write_string(&builder, ", ")
+			}
+			strings.write_string(&builder, reason.code)
+		}
+
+		strings.write_string(&builder, `]","CancellationReasons":[`)
+
+		for reason, i in result.cancellation_reasons {
+			if i > 0 {
+				strings.write_string(&builder, ",")
+			}
+			fmt.sbprintf(&builder, `{{"Code":"%s","Message":"%s"}}`, reason.code, reason.message)
+		}
+
+		strings.write_string(&builder, "]}")
+
+		response_set_status(response, .Bad_Request)
+		resp_body := strings.to_string(builder)
+		response_set_body(response, transmute([]byte)resp_body)
+
+	case .Validation_Error:
+		make_error_response(response, .ValidationException,
+			"Transaction validation failed")
+
+	case .Internal_Error:
+		make_error_response(response, .InternalServerError,
+			"Internal error during transaction")
+	}
+}
+
+// Parse a single TransactItem action from JSON
+@(private = "file")
+parse_transact_write_action :: proc(obj: json.Object) -> (dynamodb.Transact_Write_Action, bool) {
+	action: dynamodb.Transact_Write_Action
+	action.expr_attr_values = make(map[string]dynamodb.Attribute_Value)
+
+	// Try Put
+	if put_val, has_put := obj["Put"]; has_put {
+		put_obj, put_ok := put_val.(json.Object)
+		if !put_ok {
+			return {}, false
+		}
+		action.type = .Put
+		return parse_transact_put_action(put_obj, &action)
+	}
+
+	// Try Delete
+	if del_val, has_del := obj["Delete"]; has_del {
+		del_obj, del_ok := del_val.(json.Object)
+		if !del_ok {
+			return {}, false
+		}
+		action.type = .Delete
+		return parse_transact_key_action(del_obj, &action)
+	}
+
+	// Try Update
+	if upd_val, has_upd := obj["Update"]; has_upd {
+		upd_obj, upd_ok := upd_val.(json.Object)
+		if !upd_ok {
+			return {}, false
+		}
+		action.type = .Update
+		return parse_transact_update_action(upd_obj, &action)
+	}
+
+	// Try ConditionCheck
+	if cc_val, has_cc := obj["ConditionCheck"]; has_cc {
+		cc_obj, cc_ok := cc_val.(json.Object)
+		if !cc_ok {
+			return {}, false
+		}
+		action.type = .Condition_Check
+		return parse_transact_key_action(cc_obj, &action)
+	}
+
+	return {}, false
+}
+
+// Parse common expression fields from a transact action object
+@(private = "file")
+parse_transact_expression_fields :: proc(obj: json.Object, action: ^dynamodb.Transact_Write_Action) {
+	// ConditionExpression
+	if ce_val, found := obj["ConditionExpression"]; found {
+		if ce_str, str_ok := ce_val.(json.String); str_ok {
+			action.condition_expr = strings.clone(string(ce_str))
+		}
+	}
+
+	// ExpressionAttributeNames
+	if ean_val, found := obj["ExpressionAttributeNames"]; found {
+		if ean_obj, ean_ok := ean_val.(json.Object); ean_ok {
+			names := make(map[string]string)
+			for key, val in ean_obj {
+				if str, str_ok := val.(json.String); str_ok {
+					names[strings.clone(key)] = strings.clone(string(str))
+				}
+			}
+			action.expr_attr_names = names
+		}
+	}
+
+	// ExpressionAttributeValues
+	if eav_val, found := obj["ExpressionAttributeValues"]; found {
+		if eav_obj, eav_ok := eav_val.(json.Object); eav_ok {
+			for key, val in eav_obj {
+				attr, attr_ok := dynamodb.parse_attribute_value(val)
+				if attr_ok {
+					action.expr_attr_values[strings.clone(key)] = attr
+				}
+			}
+		}
+	}
+}
+
+// Parse a Put transact action
+@(private = "file")
+parse_transact_put_action :: proc(
+	obj: json.Object,
+	action: ^dynamodb.Transact_Write_Action,
+) -> (dynamodb.Transact_Write_Action, bool) {
+	// TableName
+	tn_val, tn_found := obj["TableName"]
+	if !tn_found {
+		return {}, false
+	}
+	tn_str, tn_ok := tn_val.(json.String)
+	if !tn_ok {
+		return {}, false
+	}
+	action.table_name = string(tn_str)
+
+	// Item
+	item_val, item_found := obj["Item"]
+	if !item_found {
+		return {}, false
+	}
+	item, item_ok := dynamodb.parse_item_from_value(item_val)
+	if !item_ok {
+		return {}, false
+	}
+	action.item = item
+
+	// Expression fields
+	parse_transact_expression_fields(obj, action)
+
+	return action^, true
+}
+
+// Parse a Delete or ConditionCheck transact action (both use Key)
+@(private = "file")
+parse_transact_key_action :: proc(
+	obj: json.Object,
+	action: ^dynamodb.Transact_Write_Action,
+) -> (dynamodb.Transact_Write_Action, bool) {
+	// TableName
+	tn_val, tn_found := obj["TableName"]
+	if !tn_found {
+		return {}, false
+	}
+	tn_str, tn_ok := tn_val.(json.String)
+	if !tn_ok {
+		return {}, false
+	}
+	action.table_name = string(tn_str)
+
+	// Key
+	key_val, key_found := obj["Key"]
+	if !key_found {
+		return {}, false
+	}
+	key, key_ok := dynamodb.parse_item_from_value(key_val)
+	if !key_ok {
+		return {}, false
+	}
+	action.key = key
+
+	// Expression fields
+	parse_transact_expression_fields(obj, action)
+
+	return action^, true
+}
+
+// Parse an Update transact action
+@(private = "file")
+parse_transact_update_action :: proc(
+	obj: json.Object,
+	action: ^dynamodb.Transact_Write_Action,
+) -> (dynamodb.Transact_Write_Action, bool) {
+	// TableName
+	tn_val, tn_found := obj["TableName"]
+	if !tn_found {
+		return {}, false
+	}
+	tn_str, tn_ok := tn_val.(json.String)
+	if !tn_ok {
+		return {}, false
+	}
+	action.table_name = string(tn_str)
+
+	// Key
+	key_val, key_found := obj["Key"]
+	if !key_found {
+		return {}, false
+	}
+	key, key_ok := dynamodb.parse_item_from_value(key_val)
+	if !key_ok {
+		return {}, false
+	}
+	action.key = key
+
+	// Expression fields (must be parsed before UpdateExpression so attr values are available)
+	parse_transact_expression_fields(obj, action)
+
+	// UpdateExpression
+	ue_val, ue_found := obj["UpdateExpression"]
+	if !ue_found {
+		return {}, false
+	}
+	ue_str, ue_ok := ue_val.(json.String)
+	if !ue_ok {
+		return {}, false
+	}
+
+	plan, plan_ok := dynamodb.parse_update_expression(
+		string(ue_str), action.expr_attr_names, action.expr_attr_values,
+	)
+	if !plan_ok {
+		return {}, false
+	}
+	action.update_plan = plan
+
+	return action^, true
+}
+
+// ============================================================================
+// TransactGetItems Handler
+//
+// Request format:
+// {
+//   "TransactItems": [
+//     {
+//       "Get": {
+//         "TableName": "...",
+//         "Key": { ... },
+//         "ProjectionExpression": "...",          // optional
+//         "ExpressionAttributeNames": { ... }     // optional
+//       }
+//     }
+//   ]
+// }
+// ============================================================================
+
+handle_transact_get_items :: proc(
+	engine: ^dynamodb.Storage_Engine,
+	request: ^HTTP_Request,
+	response: ^HTTP_Response,
+) {
+	data, parse_err := json.parse(request.body, allocator = context.allocator)
+	if parse_err != nil {
+		make_error_response(response, .SerializationException, "Invalid JSON")
+		return
+	}
+	defer json.destroy_value(data)
+
+	root, root_ok := data.(json.Object)
+	if !root_ok {
+		make_error_response(response, .SerializationException, "Request must be an object")
+		return
+	}
+
+	transact_items_val, found := root["TransactItems"]
+	if !found {
+		make_error_response(response, .ValidationException, "Missing TransactItems")
+		return
+	}
+
+	transact_items, ti_ok := transact_items_val.(json.Array)
+	if !ti_ok {
+		make_error_response(response, .ValidationException, "TransactItems must be an array")
+		return
+	}
+
+	if len(transact_items) == 0 {
+		make_error_response(response, .ValidationException,
+			"TransactItems must contain at least one item")
+		return
+	}
+
+	if len(transact_items) > 100 {
+		make_error_response(response, .ValidationException,
+			"Member must have length less than or equal to 100")
+		return
+	}
+
+	// Parse each get action
+	actions := make([dynamic]dynamodb.Transact_Get_Action)
+	defer {
+		for &action in actions {
+			dynamodb.transact_get_action_destroy(&action)
+		}
+		delete(actions)
+	}
+
+	for elem in transact_items {
+		elem_obj, elem_ok := elem.(json.Object)
+		if !elem_ok {
+			make_error_response(response, .ValidationException,
+				"Each TransactItem must be an object")
+			return
+		}
+
+		get_val, has_get := elem_obj["Get"]
+		if !has_get {
+			make_error_response(response, .ValidationException,
+				"TransactGetItems only supports Get actions")
+			return
+		}
+
+		get_obj, get_ok := get_val.(json.Object)
+		if !get_ok {
+			make_error_response(response, .ValidationException,
+				"Get action must be an object")
+			return
+		}
+
+		action, action_ok := parse_transact_get_action(get_obj)
+		if !action_ok {
+			make_error_response(response, .ValidationException,
+				"Invalid Get action")
+			return
+		}
+		append(&actions, action)
+	}
+
+	// Execute transaction get
+	result, tx_err := dynamodb.transact_get_items(engine, actions[:])
+	defer dynamodb.transact_get_result_destroy(&result)
+
+	if tx_err != .None {
+		make_error_response(response, .InternalServerError,
+			"Transaction get failed")
+		return
+	}
+
+	// Build response
+	builder := strings.builder_make()
+	strings.write_string(&builder, `{"Responses":[`)
+
+	for maybe_item, i in result.items {
+		if i > 0 {
+			strings.write_string(&builder, ",")
+		}
+
+		if item, has_item := maybe_item.?; has_item {
+			item_json := dynamodb.serialize_item(item)
+			fmt.sbprintf(&builder, `{{"Item":%s}}`, item_json)
+		} else {
+			strings.write_string(&builder, "{}")
+		}
+	}
+
+	strings.write_string(&builder, "]}")
+
+	resp_body := strings.to_string(builder)
+	response_set_body(response, transmute([]byte)resp_body)
+}
+
+// Parse a single TransactGetItems Get action
+@(private = "file")
+parse_transact_get_action :: proc(obj: json.Object) -> (dynamodb.Transact_Get_Action, bool) {
+	action: dynamodb.Transact_Get_Action
+
+	// TableName
+	tn_val, tn_found := obj["TableName"]
+	if !tn_found {
+		return {}, false
+	}
+	tn_str, tn_ok := tn_val.(json.String)
+	if !tn_ok {
+		return {}, false
+	}
+	action.table_name = string(tn_str)
+
+	// Key
+	key_val, key_found := obj["Key"]
+	if !key_found {
+		return {}, false
+	}
+	key, key_ok := dynamodb.parse_item_from_value(key_val)
+	if !key_ok {
+		return {}, false
+	}
+	action.key = key
+
+	// ProjectionExpression (optional)
+	if pe_val, pe_found := obj["ProjectionExpression"]; pe_found {
+		if pe_str, pe_ok := pe_val.(json.String); pe_ok {
+			// Parse ExpressionAttributeNames for projection
+			attr_names: Maybe(map[string]string) = nil
+			if ean_val, ean_found := obj["ExpressionAttributeNames"]; ean_found {
+				if ean_obj, ean_ok := ean_val.(json.Object); ean_ok {
+					names := make(map[string]string, allocator = context.temp_allocator)
+					for key_str, val in ean_obj {
+						if str, str_ok := val.(json.String); str_ok {
+							names[key_str] = string(str)
+						}
+					}
+					attr_names = names
+				}
+			}
+
+			parts := strings.split(string(pe_str), ",")
+			paths := make([dynamic]string)
+			for part in parts {
+				trimmed := strings.trim_space(part)
+				if len(trimmed) == 0 {
+					continue
+				}
+				resolved, res_ok := dynamodb.resolve_attribute_name(trimmed, attr_names)
+				if !res_ok {
+					delete(paths)
+					dynamodb.item_destroy(&action.key)
+					return {}, false
+				}
+				append(&paths, strings.clone(resolved))
+			}
+			action.projection = paths[:]
+		}
+	}
+
+	return action, true
+}
+
+// ============================================================================
+// UPDATED_NEW / UPDATED_OLD Filtering Helper
+//
+// DynamoDB ReturnValues semantics:
+//   ALL_NEW      → all attributes of the item after the update
+//   ALL_OLD      → all attributes of the item before the update
+//   UPDATED_NEW  → only the attributes that were modified, with new values
+//   UPDATED_OLD  → only the attributes that were modified, with old values
+//
+// This filters an item to only include the attributes touched by the
+// UpdateExpression (the "modified paths").
+// ============================================================================
+
+filter_updated_attributes :: proc(
+	item: dynamodb.Item,
+	plan: ^dynamodb.Update_Plan,
+) -> dynamodb.Item {
+	modified_paths := dynamodb.get_update_plan_modified_paths(plan)
+	defer delete(modified_paths)
+
+	return dynamodb.filter_item_to_paths(item, modified_paths)
+}