From 42e274124f677193dac9fb04be70bd68c5b73b58 Mon Sep 17 00:00:00 2001
From: Nikolay Karadzhov <nkaradzhov89@gmail.com>
Date: Wed, 22 Jul 2026 14:34:03 +0300
Subject: [PATCH] feat(search): add RERANK parameter for HNSW vector fields

Add the optional RERANK boolean to HNSW vector field definitions in
FT.CREATE, introduced in Redis 8.10 for disk-based vector indexes. When
set, the client emits `RERANK TRUE` / `RERANK FALSE`; it is only sent
when explicitly provided. The parameter is HNSW-only and confined to the
HNSW schema type.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 packages/search/lib/commands/CREATE.spec.ts | 57 +++++++++++++++++++++
 packages/search/lib/commands/CREATE.ts      |  9 ++++
 2 files changed, 66 insertions(+)

diff --git a/packages/search/lib/commands/CREATE.spec.ts b/packages/search/lib/commands/CREATE.spec.ts
index 833044f0baa..803fdb33339 100644
--- a/packages/search/lib/commands/CREATE.spec.ts
+++ b/packages/search/lib/commands/CREATE.spec.ts
@@ -207,6 +207,44 @@ describe('FT.CREATE', () => {
           );
         });
 
+        it('HNSW algorithm with RERANK', () => {
+          assert.deepEqual(
+            parseArgs(CREATE, 'index', {
+              field: {
+                type: SCHEMA_FIELD_TYPE.VECTOR,
+                ALGORITHM: SCHEMA_VECTOR_FIELD_ALGORITHM.HNSW,
+                TYPE: 'FLOAT32',
+                DIM: 2,
+                DISTANCE_METRIC: 'L2',
+                RERANK: true
+              }
+            }),
+            [
+              'FT.CREATE', 'index', 'SCHEMA', 'field', 'VECTOR', 'HNSW', '8', 'TYPE',
+              'FLOAT32', 'DIM', '2', 'DISTANCE_METRIC', 'L2', 'RERANK', 'TRUE'
+            ]
+          );
+        });
+
+        it('HNSW algorithm with RERANK false', () => {
+          assert.deepEqual(
+            parseArgs(CREATE, 'index', {
+              field: {
+                type: SCHEMA_FIELD_TYPE.VECTOR,
+                ALGORITHM: SCHEMA_VECTOR_FIELD_ALGORITHM.HNSW,
+                TYPE: 'FLOAT32',
+                DIM: 2,
+                DISTANCE_METRIC: 'L2',
+                RERANK: false
+              }
+            }),
+            [
+              'FT.CREATE', 'index', 'SCHEMA', 'field', 'VECTOR', 'HNSW', '8', 'TYPE',
+              'FLOAT32', 'DIM', '2', 'DISTANCE_METRIC', 'L2', 'RERANK', 'FALSE'
+            ]
+          );
+        });
+
         it('VAMANA algorithm', () => {
           assert.deepEqual(
             parseArgs(CREATE, 'index', {
@@ -642,6 +680,25 @@ describe('FT.CREATE', () => {
     );
   }, GLOBAL.SERVERS.OPEN);
 
+  testUtils.testWithClientIfVersionWithinRange([[8, 10], 'LATEST'], 'client.ft.create vector hnsw rerank', async client => {
+    // RERANK is only valid for disk-based vector indexes, which the OSS test
+    // server cannot create. Assert the parameter reaches the server and is
+    // recognized (rejected only for the index type, not as a syntax error).
+    await assert.rejects(
+      client.ft.create('index_hnsw_rerank', {
+        field: {
+          type: SCHEMA_FIELD_TYPE.VECTOR,
+          ALGORITHM: SCHEMA_VECTOR_FIELD_ALGORITHM.HNSW,
+          TYPE: 'FLOAT32',
+          DIM: 5,
+          DISTANCE_METRIC: 'L2',
+          RERANK: true
+        },
+      }),
+      /disk-based/
+    );
+  }, GLOBAL.SERVERS.OPEN);
+
   testUtils.testWithClientIfVersionWithinRange([[8, 2], 'LATEST'], 'client.ft.create vector svs-vamana', async client => {
     assert.equal(
       await client.ft.create("index_svs_vamana_min_config", {
diff --git a/packages/search/lib/commands/CREATE.ts b/packages/search/lib/commands/CREATE.ts
index 00dee3ef975..34aeb49393f 100644
--- a/packages/search/lib/commands/CREATE.ts
+++ b/packages/search/lib/commands/CREATE.ts
@@ -81,6 +81,11 @@ interface SchemaHNSWVectorField extends SchemaVectorField {
   M?: number;
   EF_CONSTRUCTION?: number;
   EF_RUNTIME?: number;
+  /**
+   * Enable reranking. Requires a disk-based vector index.
+   * available since 8.10
+   */
+  RERANK?: boolean;
 }
 
 export const VAMANA_COMPRESSION_ALGORITHM = {
@@ -293,6 +298,10 @@ export function parseSchema(parser: CommandParser, schema: RediSearchSchema) {
                 args.push('EF_RUNTIME', fieldOptions.EF_RUNTIME.toString());
               }
 
+              if (fieldOptions.RERANK !== undefined) {
+                args.push('RERANK', fieldOptions.RERANK ? 'TRUE' : 'FALSE');
+              }
+
               break;
 
             case SCHEMA_VECTOR_FIELD_ALGORITHM['VAMANA']: