Started support for parallel index scan [skip ci]

.github/workflows/build.yml

@@ -23,7 +23,7 @@ jobs:
           - postgres: 13
             os: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v4
       - uses: ankane/setup-postgres@v1
         with:
           postgres-version: ${{ matrix.postgres }}
@@ -53,7 +53,7 @@ jobs:
           - postgres: 14
             os: macos-15-intel
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v4
       - uses: ankane/setup-postgres@v1
         with:
           postgres-version: ${{ matrix.postgres }}
@@ -92,7 +92,7 @@ jobs:
           - postgres: 14
             os: windows-2022
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v4
       - uses: ankane/setup-postgres@v1
         with:
           postgres-version: ${{ matrix.postgres }}
@@ -133,7 +133,7 @@ jobs:
     if: ${{ !startsWith(github.ref_name, 'mac') && !startsWith(github.ref_name, 'windows') }}
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v4
       - uses: ankane/setup-postgres-valgrind@v1
         with:
           postgres-version: 17

CHANGELOG.md

@@ -1,7 +1,3 @@
-## 0.8.2 (unreleased)
-
-- Improved performance of HNSW index scans from disk
-
 ## 0.8.1 (2025-09-04)
 
 - Added support for Postgres 18 rc1

README.md

@@ -1267,7 +1267,6 @@ Thanks to:
 - [k-means++: The Advantage of Careful Seeding](https://theory.stanford.edu/~sergei/papers/kMeansPP-soda.pdf)
 - [Concept Decompositions for Large Sparse Text Data using Clustering](https://www.cs.utexas.edu/users/inderjit/public_papers/concept_mlj.pdf)
 - [Efficient and Robust Approximate Nearest Neighbor Search using Hierarchical Navigable Small World Graphs](https://arxiv.org/ftp/arxiv/papers/1603/1603.09320.pdf)
-- [Turbocharging Vector Databases using Modern SSDs](https://www.vldb.org/pvldb/volumes/18/paper/Turbocharging%20Vector%20Databases%20using%20Modern%20SSDs)
 
 ## History
 

src/hnswbuild.c

@@ -131,69 +131,6 @@ HnswBuildAppendPage(Relation index, Buffer *buf, Page *page, ForkNumber forkNum)
 	HnswInitPage(*buf, *page);
 }
 
-static void
-WriteElement(char *base, HnswElement element, HnswElementTuple etup, HnswNeighborTuple ntup, HnswBuildState * buildstate, Size maxSize, Buffer *buf, Page *page, Relation index, ForkNumber forkNum)
-{
-	Size		etupSize;
-	Size		ntupSize;
-	Size		combinedSize;
-	Pointer		valuePtr;
-
-	/* Skip if already added */
-	if (BlockNumberIsValid(element->neighborPage))
-		return;
-
-	valuePtr = HnswPtrAccess(base, element->value);
-
-	/* Zero memory for each element */
-	MemSet(etup, 0, HNSW_TUPLE_ALLOC_SIZE);
-
-	/* Calculate sizes */
-	etupSize = HNSW_ELEMENT_TUPLE_SIZE(VARSIZE_ANY(valuePtr));
-	ntupSize = HNSW_NEIGHBOR_TUPLE_SIZE(element->level, buildstate->m);
-	combinedSize = etupSize + ntupSize + sizeof(ItemIdData);
-
-	/* Initial size check */
-	if (etupSize > HNSW_TUPLE_ALLOC_SIZE)
-		ereport(ERROR,
-				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
-				 errmsg("index tuple too large")));
-
-	HnswSetElementTuple(base, etup, element);
-
-	/* Keep element and neighbors on the same page if possible */
-	if (PageGetFreeSpace(*page) < etupSize || (combinedSize <= maxSize && PageGetFreeSpace(*page) < combinedSize))
-		HnswBuildAppendPage(index, buf, page, forkNum);
-
-	/* Calculate offsets */
-	element->blkno = BufferGetBlockNumber(*buf);
-	element->offno = OffsetNumberNext(PageGetMaxOffsetNumber(*page));
-	if (combinedSize <= maxSize)
-	{
-		element->neighborPage = element->blkno;
-		element->neighborOffno = OffsetNumberNext(element->offno);
-	}
-	else
-	{
-		element->neighborPage = element->blkno + 1;
-		element->neighborOffno = FirstOffsetNumber;
-	}
-
-	ItemPointerSet(&etup->neighbortid, element->neighborPage, element->neighborOffno);
-
-	/* Add element */
-	if (PageAddItem(*page, (Item) etup, etupSize, InvalidOffsetNumber, false, false) != element->offno)
-		elog(ERROR, "failed to add index item to \"%s\"", RelationGetRelationName(index));
-
-	/* Add new page if needed */
-	if (PageGetFreeSpace(*page) < ntupSize)
-		HnswBuildAppendPage(index, buf, page, forkNum);
-
-	/* Add placeholder for neighbors */
-	if (PageAddItem(*page, (Item) ntup, ntupSize, InvalidOffsetNumber, false, false) != element->neighborOffno)
-		elog(ERROR, "failed to add index item to \"%s\"", RelationGetRelationName(index));
-}
-
 /*
  * Create graph pages
  */
@@ -227,24 +164,61 @@ CreateGraphPages(HnswBuildState * buildstate)
 	while (!HnswPtrIsNull(base, iter))
 	{
 		HnswElement element = HnswPtrAccess(base, iter);
+		Size		etupSize;
+		Size		ntupSize;
+		Size		combinedSize;
+		Pointer		valuePtr = HnswPtrAccess(base, element->value);
 
 		/* Update iterator */
 		iter = element->next;
 
-		WriteElement(base, element, etup, ntup, buildstate, maxSize, &buf, &page, index, forkNum);
+		/* Zero memory for each element */
+		MemSet(etup, 0, HNSW_TUPLE_ALLOC_SIZE);
 
-		for (int lc = element->level; lc >= 0; lc--)
+		/* Calculate sizes */
+		etupSize = HNSW_ELEMENT_TUPLE_SIZE(VARSIZE_ANY(valuePtr));
+		ntupSize = HNSW_NEIGHBOR_TUPLE_SIZE(element->level, buildstate->m);
+		combinedSize = etupSize + ntupSize + sizeof(ItemIdData);
+
+		/* Initial size check */
+		if (etupSize > HNSW_TUPLE_ALLOC_SIZE)
+			ereport(ERROR,
+					(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+					 errmsg("index tuple too large")));
+
+		HnswSetElementTuple(base, etup, element);
+
+		/* Keep element and neighbors on the same page if possible */
+		if (PageGetFreeSpace(page) < etupSize || (combinedSize <= maxSize && PageGetFreeSpace(page) < combinedSize))
+			HnswBuildAppendPage(index, &buf, &page, forkNum);
+
+		/* Calculate offsets */
+		element->blkno = BufferGetBlockNumber(buf);
+		element->offno = OffsetNumberNext(PageGetMaxOffsetNumber(page));
+		if (combinedSize <= maxSize)
 		{
-			HnswNeighborArray *neighbors = HnswGetNeighbors(base, element, lc);
-
-			for (int i = 0; i < neighbors->length; i++)
-			{
-				HnswCandidate *hc = &neighbors->items[i];
-				HnswElement hce = HnswPtrAccess(base, hc->element);
-
-				WriteElement(base, hce, etup, ntup, buildstate, maxSize, &buf, &page, index, forkNum);
-			}
+			element->neighborPage = element->blkno;
+			element->neighborOffno = OffsetNumberNext(element->offno);
 		}
+		else
+		{
+			element->neighborPage = element->blkno + 1;
+			element->neighborOffno = FirstOffsetNumber;
+		}
+
+		ItemPointerSet(&etup->neighbortid, element->neighborPage, element->neighborOffno);
+
+		/* Add element */
+		if (PageAddItem(page, (Item) etup, etupSize, InvalidOffsetNumber, false, false) != element->offno)
+			elog(ERROR, "failed to add index item to \"%s\"", RelationGetRelationName(index));
+
+		/* Add new page if needed */
+		if (PageGetFreeSpace(page) < ntupSize)
+			HnswBuildAppendPage(index, &buf, &page, forkNum);
+
+		/* Add placeholder for neighbors */
+		if (PageAddItem(page, (Item) ntup, ntupSize, InvalidOffsetNumber, false, false) != element->neighborOffno)
+			elog(ERROR, "failed to add index item to \"%s\"", RelationGetRelationName(index));
 	}
 
 	insertPage = BufferGetBlockNumber(buf);

src/hnswutils.c

@@ -253,7 +253,6 @@ HnswInitElement(char *base, ItemPointer heaptid, int m, double ml, int maxLevel,
 	element->deleted = 0;
 	/* Start at one to make it easier to find issues */
 	element->version = 1;
-	element->neighborPage = InvalidBlockNumber;
 
 	HnswInitNeighbors(base, element, m, allocator);
 

src/ivfflat.c

@@ -143,6 +143,10 @@ ivfflatcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
 	*indexSelectivity = costs.indexSelectivity;
 	*indexCorrelation = costs.indexCorrelation;
 	*indexPages = costs.numIndexPages;
+
+	elog(INFO, "ivfflatcostestimate = %f", costs.indexTotalCost);
+	/* Cost estimates for parallel workers applied outside of amcostestimate */
+	elog(INFO, "parallel_workers = %d, parallel aware = %d", path->path.parallel_workers, path->path.parallel_aware);
 }
 
 /*
@@ -170,6 +174,25 @@ ivfflatvalidate(Oid opclassoid)
 	return true;
 }
 
+static Size
+ivfflatestimateparallelscan()
+{
+	elog(INFO, "ivfflatestimateparallelscan");
+	return 0;
+}
+
+static void
+ivfflatinitparallelscan(void *target)
+{
+	elog(INFO, "ivfflatinitparallelscan");
+}
+
+static void
+ivfflatparallelrescan(IndexScanDesc scan)
+{
+	elog(INFO, "ivfflatparallelrescan");
+}
+
 /*
  * Define index handler
  *
@@ -200,7 +223,7 @@ ivfflathandler(PG_FUNCTION_ARGS)
 	amroutine->amstorage = false;
 	amroutine->amclusterable = false;
 	amroutine->ampredlocks = false;
-	amroutine->amcanparallel = false;
+	amroutine->amcanparallel = true;
 #if PG_VERSION_NUM >= 170000
 	amroutine->amcanbuildparallel = true;
 #endif
@@ -242,9 +265,9 @@ ivfflathandler(PG_FUNCTION_ARGS)
 	amroutine->amrestrpos = NULL;
 
 	/* Interface functions to support parallel index scans */
-	amroutine->amestimateparallelscan = NULL;
-	amroutine->aminitparallelscan = NULL;
-	amroutine->amparallelrescan = NULL;
+	amroutine->amestimateparallelscan = ivfflatestimateparallelscan;
+	amroutine->aminitparallelscan = ivfflatinitparallelscan;
+	amroutine->amparallelrescan = ivfflatparallelrescan;
 
 #if PG_VERSION_NUM >= 180000
 	amroutine->amtranslatestrategy = NULL;

src/ivfscan.c

@@ -119,6 +119,9 @@ GetScanItems(IndexScanDesc scan, Datum value)
 
 	tuplesort_reset(so->sortstate);
 
+	if (scan->parallel_scan != NULL)
+		elog(INFO, "parallel scan");
+
 	/* Search closest probes lists */
 	while (so->listIndex < so->maxProbes && (++batchProbes) <= so->probes)
 	{

test/sql/ivfflat_parallel.sql

@@ -0,0 +1,16 @@
+-- SET force_parallel_mode = on;
+SET parallel_setup_cost = 10;
+SET parallel_tuple_cost = 0.000001;
+SET min_parallel_table_scan_size = 1;
+SET min_parallel_index_scan_size = 1;
+
+CREATE TABLE t (id integer, val vector(3));
+ALTER TABLE t ALTER COLUMN val SET STORAGE PLAIN;
+INSERT INTO t (id, val) SELECT n, ARRAY[random(), random(), random()] FROM generate_series(1,1000000) n;
+CREATE INDEX ON t USING ivfflat (val) WITH (lists = 10);
+SET ivfflat.probes = 4;
+
+EXPLAIN SELECT * FROM t ORDER BY val <-> '[0.5,0.5,0.5]' LIMIT 5;
+SELECT * FROM t ORDER BY val <-> '[0.5,0.5,0.5]' LIMIT 5;
+
+DROP TABLE t;