Do not use index if no limit or limit + offset > expected tuples unless enable_seqscan = off

This reverts commit 4894dc5da1.

CHANGELOG.md

@@ -2,7 +2,9 @@
 
 - Improved performance of HNSW
 - Added support for on-disk parallel index builds for HNSW
+- Reduced memory usage for HNSW index builds
 - Reduced WAL generation for HNSW index builds
+- Fixed error with logical replication
 - Fixed `invalid memory alloc request size` error with HNSW index build
 
 ## 0.5.1 (2023-10-10)

README.md

@@ -161,80 +161,12 @@ You can add an index to use approximate nearest neighbor search, which trades so
 
 Supported index types are:
 
-- [IVFFlat](#ivfflat)
 - [HNSW](#hnsw) - added in 0.5.0
-
+- [IVFFlat](#ivfflat)
-## IVFFlat
-
-An IVFFlat index divides vectors into lists, and then searches a subset of those lists that are closest to the query vector. It has faster build times and uses less memory than HNSW, but has lower query performance (in terms of speed-recall tradeoff).
-
-Three keys to achieving good recall are:
-
-1. Create the index *after* the table has some data
-2. Choose an appropriate number of lists - a good place to start is `rows / 1000` for up to 1M rows and `sqrt(rows)` for over 1M rows
-3. When querying, specify an appropriate number of [probes](#query-options) (higher is better for recall, lower is better for speed) - a good place to start is `sqrt(lists)`
-
-Add an index for each distance function you want to use.
-
-L2 distance
-
-```sql
-CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops) WITH (lists = 100);
-```
-
-Inner product
-
-```sql
-CREATE INDEX ON items USING ivfflat (embedding vector_ip_ops) WITH (lists = 100);
-```
-
-Cosine distance
-
-```sql
-CREATE INDEX ON items USING ivfflat (embedding vector_cosine_ops) WITH (lists = 100);
-```
-
-Vectors with up to 2,000 dimensions can be indexed.
-
-### Query Options
-
-Specify the number of probes (1 by default)
-
-```sql
-SET ivfflat.probes = 10;
-```
-
-A higher value provides better recall at the cost of speed, and it can be set to the number of lists for exact nearest neighbor search (at which point the planner won’t use the index)
-
-Use `SET LOCAL` inside a transaction to set it for a single query
-
-```sql
-BEGIN;
-SET LOCAL ivfflat.probes = 10;
-SELECT ...
-COMMIT;
-```
-
-### Indexing Progress
-
-Check [indexing progress](https://www.postgresql.org/docs/current/progress-reporting.html#CREATE-INDEX-PROGRESS-REPORTING) with Postgres 12+
-
-```sql
-SELECT phase, round(100.0 * tuples_done / nullif(tuples_total, 0), 1) AS "%" FROM pg_stat_progress_create_index;
-```
-
-The phases for IVFFlat are:
-
-1. `initializing`
-2. `performing k-means`
-3. `assigning tuples`
-4. `loading tuples`
-
-Note: `%` is only populated during the `loading tuples` phase
 
 ## HNSW
 
-An HNSW index creates a multilayer graph. It has slower build times and uses more memory than IVFFlat, but has better query performance (in terms of speed-recall tradeoff). There’s no training step like IVFFlat, so the index can be created without any data in the table.
+An HNSW index creates a multilayer graph. It has better query performance than IVFFlat (in terms of speed-recall tradeoff), but has slower build times and uses more memory. Also, an index can be created without any data in the table since there isn’t a training step like IVFFlat.
 
 Add an index for each distance function you want to use.
 
@@ -290,6 +222,24 @@ SELECT ...
 COMMIT;
 ```
 
+### Index Build Time
+
+Indexes build significantly faster when the graph fits into `maintenance_work_mem`
+
+```sql
+SET maintenance_work_mem = '8GB';
+```
+
+A notice is shown when the graph no longer fits
+
+```text
+NOTICE:  hnsw graph no longer fits into maintenance_work_mem after 100000 tuples
+DETAIL:  Building will take significantly more time.
+HINT:  Increase maintenance_work_mem to speed up builds.
+```
+
+Note: Do not set `maintenance_work_mem` so high that it exhausts the memory on the server
+
 ### Indexing Progress
 
 Check [indexing progress](https://www.postgresql.org/docs/current/progress-reporting.html#CREATE-INDEX-PROGRESS-REPORTING) with Postgres 12+
@@ -303,6 +253,84 @@ The phases for HNSW are:
 1. `initializing`
 2. `loading tuples`
 
+## IVFFlat
+
+An IVFFlat index divides vectors into lists, and then searches a subset of those lists that are closest to the query vector. It has faster build times and uses less memory than HNSW, but has lower query performance (in terms of speed-recall tradeoff).
+
+Three keys to achieving good recall are:
+
+1. Create the index *after* the table has some data
+2. Choose an appropriate number of lists - a good place to start is `rows / 1000` for up to 1M rows and `sqrt(rows)` for over 1M rows
+3. When querying, specify an appropriate number of [probes](#query-options) (higher is better for recall, lower is better for speed) - a good place to start is `sqrt(lists)`
+
+Add an index for each distance function you want to use.
+
+L2 distance
+
+```sql
+CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops) WITH (lists = 100);
+```
+
+Inner product
+
+```sql
+CREATE INDEX ON items USING ivfflat (embedding vector_ip_ops) WITH (lists = 100);
+```
+
+Cosine distance
+
+```sql
+CREATE INDEX ON items USING ivfflat (embedding vector_cosine_ops) WITH (lists = 100);
+```
+
+Vectors with up to 2,000 dimensions can be indexed.
+
+### Query Options
+
+Specify the number of probes (1 by default)
+
+```sql
+SET ivfflat.probes = 10;
+```
+
+A higher value provides better recall at the cost of speed, and it can be set to the number of lists for exact nearest neighbor search (at which point the planner won’t use the index)
+
+Use `SET LOCAL` inside a transaction to set it for a single query
+
+```sql
+BEGIN;
+SET LOCAL ivfflat.probes = 10;
+SELECT ...
+COMMIT;
+```
+
+### Index Build Time
+
+Speed up index creation on large tables by increasing the number of parallel workers (2 by default)
+
+```sql
+SET max_parallel_maintenance_workers = 7; -- plus leader
+```
+
+For a large number of workers, you may also need to increase `max_parallel_workers` (8 by default)
+
+### Indexing Progress
+
+Check [indexing progress](https://www.postgresql.org/docs/current/progress-reporting.html#CREATE-INDEX-PROGRESS-REPORTING) with Postgres 12+
+
+```sql
+SELECT phase, round(100.0 * tuples_done / nullif(tuples_total, 0), 1) AS "%" FROM pg_stat_progress_create_index;
+```
+
+The phases for IVFFlat are:
+
+1. `initializing`
+2. `performing k-means`
+3. `assigning tuples`
+4. `loading tuples`
+
+Note: `%` is only populated during the `loading tuples` phase
+
 ## Filtering
 
 There are a few ways to index nearest neighbor queries with a `WHERE` clause
@@ -320,8 +348,7 @@ CREATE INDEX ON items (category_id);
 Or a [partial index](https://www.postgresql.org/docs/current/indexes-partial.html) on the vector column for approximate search
 
 ```sql
-CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops) WITH (lists = 100)
+CREATE INDEX ON items USING hnsw (embedding vector_l2_ops) WHERE (category_id = 123);
-    WHERE (category_id = 123);
 ```
 
 Use [partitioning](https://www.postgresql.org/docs/current/ddl-partitioning.html) for approximate search on many different values of the `WHERE` columns
@@ -555,7 +582,7 @@ sum(vector) → vector | sum | 0.5.0
 If your machine has multiple Postgres installations, specify the path to [pg_config](https://www.postgresql.org/docs/current/app-pgconfig.html) with:
 
 ```sh
-export PG_CONFIG=/Applications/Postgres.app/Contents/Versions/latest/bin/pg_config
+export PG_CONFIG=/Library/PostgreSQL/16/bin/pg_config
 ```
 
 Then re-run the installation instructions (run `make clean` before `make` if needed). If `sudo` is needed for `make install`, use:
@@ -564,6 +591,14 @@ Then re-run the installation instructions (run `make clean` before `make` if nee
 sudo --preserve-env=PG_CONFIG make install
 ```
 
+A few common paths on Mac are:
+
+- EDB installer - `/Library/PostgreSQL/16/bin/pg_config`
+- Homebrew (arm64) - `/opt/homebrew/opt/postgresql@16/bin/pg_config`
+- Homebrew (x86-64) - `/usr/local/opt/postgresql@16/bin/pg_config`
+
+Note: Replace `16` with your Postgres server version
+
 ### Missing Header
 
 If compilation fails with `fatal error: postgres.h: No such file or directory`, make sure Postgres development files are installed on the server.
@@ -571,10 +606,14 @@ If compilation fails with `fatal error: postgres.h: No such file or directory`,
 For Ubuntu and Debian, use:
 
 ```sh
-sudo apt install postgresql-server-dev-15
+sudo apt install postgresql-server-dev-16
 ```
 
-Note: Replace `15` with your Postgres server version
+Note: Replace `16` with your Postgres server version
+
+### Missing SDK
+
+If compilation fails and the output includes `warning: no such sysroot directory` on Mac, reinstall Xcode Command Line Tools.
 
 ### Windows
 
@@ -589,7 +628,7 @@ Note: The exact path will vary depending on your Visual Studio version and editi
 Then use `nmake` to build:
 
 ```cmd
-set "PGROOT=C:\Program Files\PostgreSQL\15"
+set "PGROOT=C:\Program Files\PostgreSQL\16"
 git clone --branch v0.5.1 https://github.com/pgvector/pgvector.git
 cd pgvector
 nmake /F Makefile.win
@@ -639,22 +678,22 @@ pgxn install vector
 Debian and Ubuntu packages are available from the [PostgreSQL APT Repository](https://wiki.postgresql.org/wiki/Apt). Follow the [setup instructions](https://wiki.postgresql.org/wiki/Apt#Quickstart) and run:
 
 ```sh
-sudo apt install postgresql-15-pgvector
+sudo apt install postgresql-16-pgvector
 ```
 
-Note: Replace `15` with your Postgres server version
+Note: Replace `16` with your Postgres server version
 
 ### Yum
 
 RPM packages are available from the [PostgreSQL Yum Repository](https://yum.postgresql.org/). Follow the [setup instructions](https://www.postgresql.org/download/linux/redhat/) for your distribution and run:
 
 ```sh
-sudo yum install pgvector_15
+sudo yum install pgvector_16
 # or
-sudo dnf install pgvector_15
+sudo dnf install pgvector_16
 ```
 
-Note: Replace `15` with your Postgres server version
+Note: Replace `16` with your Postgres server version
 
 ### conda-forge
 
@@ -764,7 +803,25 @@ make prove_installcheck PROVE_TESTS=test/t/001_wal.pl  # TAP test
 To enable benchmarking:
 
 ```sh
-make clean && PG_CFLAGS=-DIVFFLAT_BENCH make && make install
+make clean && PG_CFLAGS="-DIVFFLAT_BENCH" make && make install
+```
+
+To show memory usage:
+
+```sh
+make clean && PG_CFLAGS="-DHNSW_MEMORY -DIVFFLAT_MEMORY" make && make install
+```
+
+To enable assertions:
+
+```sh
+make clean && PG_CFLAGS="-DUSE_ASSERT_CHECKING" make && make install
+```
+
+To get k-means metrics:
+
+```sh
+make clean && PG_CFLAGS="-DIVFFLAT_KMEANS_DEBUG" make && make install
 ```
 
 Resources for contributors

src/hnsw.c

@@ -94,6 +94,20 @@ hnswcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
 		return;
 	}
 
+	/*
+	 * Do not use index if no limit or limit + offset > ef_search unless
+	 * enable_seqscan = off
+	 */
+	if (root->limit_tuples < 0 || root->limit_tuples > hnsw_ef_search)
+	{
+		*indexStartupCost = 1.0e10 - 1;
+		*indexTotalCost = 1.0e10 - 1;
+		*indexSelectivity = 0;
+		*indexCorrelation = 0;
+		*indexPages = 0;
+		return;
+	}
+
 	MemSet(&costs, 0, sizeof(costs));
 
 	index = index_open(path->indexinfo->indexoid, NoLock);

src/hnsw.h

@@ -6,6 +6,7 @@
 #include "access/generic_xlog.h"
 #include "access/parallel.h"
 #include "access/reloptions.h"
+#include "lib/ilist.h"
 #include "nodes/execnodes.h"
 #include "port.h"				/* for random() */
 #include "utils/sampling.h"
@@ -72,8 +73,10 @@
 
 #if PG_VERSION_NUM >= 150000
 #define RandomDouble() pg_prng_double(&pg_global_prng_state)
+#define SeedRandom(seed) pg_prng_seed(&pg_global_prng_state, seed)
 #else
 #define RandomDouble() (((double) random()) / MAX_RANDOM_VALUE)
+#define SeedRandom(seed) srandom(seed)
 #endif
 
 #if PG_VERSION_NUM < 130000
@@ -91,21 +94,23 @@
 #define HnswGetMl(m) (1 / log(m))
 
 /* Ensure fits on page and in uint8 */
-#define HnswGetMaxLevel(m) Min(((BLCKSZ - MAXALIGN(SizeOfPageHeaderData) - MAXALIGN(sizeof(HnswPageOpaqueData)) - offsetof(HnswNeighborTupleData, indextids) - sizeof(ItemIdData)) / (sizeof(ItemPointerData)) / m) - 2, 255)
+#define HnswGetMaxLevel(m) Min(((BLCKSZ - MAXALIGN(SizeOfPageHeaderData) - MAXALIGN(sizeof(HnswPageOpaqueData)) - offsetof(HnswNeighborTupleData, indextids) - sizeof(ItemIdData)) / (sizeof(ItemPointerData)) / (m)) - 2, 255)
+
+#define HnswGetNeighbors(element, lc) (AssertMacro((element)->level >= (lc)), &(element)->neighbors[lc])
 
 /* Variables */
 extern int	hnsw_ef_search;
 extern bool hnsw_enable_parallel_build;
 
-typedef struct HnswNeighborArray HnswNeighborArray;
-
 typedef struct HnswElementData
 {
-	List	   *heaptids;
+	slist_node	next;
+	ItemPointerData heaptids[HNSW_HEAPTIDS];
+	uint8		heaptidsLength;
 	uint8		level;
 	uint8		deleted;
 	uint32		hash;
-	HnswNeighborArray *neighbors;
+	struct HnswNeighborArray *neighbors;
 	BlockNumber blkno;
 	OffsetNumber offno;
 	OffsetNumber neighborOffno;
@@ -143,6 +148,16 @@ typedef struct HnswOptions
 	int			efConstruction; /* size of dynamic candidate list */
 }			HnswOptions;
 
+typedef struct HnswGraph
+{
+	slist_head	elements;
+	HnswElement entryPoint;
+	long		memoryUsed;
+	long		memoryTotal;
+	bool		flushed;
+	double		indtuples;
+}			HnswGraph;
+
 typedef struct HnswSpool
 {
 	Relation	heap;
@@ -166,7 +181,7 @@ typedef struct HnswShared
 	/* Mutable state */
 	int			nparticipantsdone;
 	double		reltuples;
-	double		indtuples;
+	HnswGraph	graphData;
 
 #if PG_VERSION_NUM < 120000
 	ParallelHeapScanDescData heapdesc;	/* must come last */
@@ -209,15 +224,14 @@ typedef struct HnswBuildState
 	Oid			collation;
 
 	/* Variables */
-	List	   *elements;
+	HnswGraph	graphData;
-	HnswElement entryPoint;
+	HnswGraph  *graph;
 	double		ml;
 	int			maxLevel;
-	long		memoryLeft;
-	bool		flushed;
 	Vector	   *normvec;
 
 	/* Memory */
+	MemoryContext graphCtx;
 	MemoryContext tmpCtx;
 
 	/* Parallel builds */
@@ -325,10 +339,8 @@ List	   *HnswSearchLayer(Datum q, List *ep, int ef, int lc, Relation index, Fmgr
 HnswElement HnswGetEntryPoint(Relation index);
 void		HnswGetMetaPageInfo(Relation index, int *m, HnswElement * entryPoint);
 HnswElement HnswInitElement(ItemPointer tid, int m, double ml, int maxLevel);
-void		HnswFreeElement(HnswElement element);
 HnswElement HnswInitElementFromBlock(BlockNumber blkno, OffsetNumber offno);
 void		HnswInsertElement(HnswElement element, HnswElement entryPoint, Relation index, FmgrInfo *procinfo, Oid collation, int m, int efConstruction, bool existing);
-HnswElement HnswFindDuplicate(HnswElement e);
 HnswCandidate *HnswEntryCandidate(HnswElement em, Datum q, Relation rel, FmgrInfo *procinfo, Oid collation, bool loadVec);
 void		HnswUpdateMetaPage(Relation index, int updateEntry, HnswElement entryPoint, BlockNumber insertPage, ForkNumber forkNum, bool building);
 void		HnswSetNeighborTuple(HnswNeighborTuple ntup, HnswElement e, int m);

src/hnswbuild.c

@@ -56,7 +56,9 @@
 #define PARALLEL_KEY_HNSW_SHARED		UINT64CONST(0xA000000000000001)
 #define PARALLEL_KEY_QUERY_TEXT			UINT64CONST(0xA000000000000002)
 
-#define LIST_MAX_LENGTH ((1 << 26) - 1)
+#if PG_VERSION_NUM < 130000
+#define GENERATIONCHUNK_RAWSIZE (SIZEOF_SIZE_T + SIZEOF_VOID_P * 2)
+#endif
 
 /*
  * Create the metapage
@@ -88,6 +90,7 @@ CreateMetaPage(HnswBuildState * buildstate)
 	((PageHeader) page)->pd_lower =
 		((char *) metap + sizeof(HnswMetaPageData)) - (char *) page;
 
+	MarkBufferDirty(buf);
 	UnlockReleaseBuffer(buf);
 }
 
@@ -104,6 +107,7 @@ HnswBuildAppendPage(Relation index, Buffer *buf, Page *page, ForkNumber forkNum)
 	HnswPageGetOpaque(*page)->nextblkno = BufferGetBlockNumber(newbuf);
 
 	/* Commit */
+	MarkBufferDirty(*buf);
 	UnlockReleaseBuffer(*buf);
 
 	/* Can take a while, so ensure we can interrupt */
@@ -133,7 +137,7 @@ CreateElementPages(HnswBuildState * buildstate)
 	BlockNumber insertPage;
 	Buffer		buf;
 	Page		page;
-	ListCell   *lc;
+	slist_iter	iter;
 
 	/* Calculate sizes */
 	etupAllocSize = BLCKSZ;
@@ -148,9 +152,9 @@ CreateElementPages(HnswBuildState * buildstate)
 	page = BufferGetPage(buf);
 	HnswInitPage(buf, page);
 
-	foreach(lc, buildstate->elements)
+	slist_foreach(iter, &buildstate->graph->elements)
 	{
-		HnswElement element = lfirst(lc);
+		HnswElement element = slist_container(HnswElementData, next, iter.cur);
 		Size		etupSize;
 		Size		ntupSize;
 		Size		combinedSize;
@@ -205,9 +209,10 @@ CreateElementPages(HnswBuildState * buildstate)
 	insertPage = BufferGetBlockNumber(buf);
 
 	/* Commit */
+	MarkBufferDirty(buf);
 	UnlockReleaseBuffer(buf);
 
-	HnswUpdateMetaPage(index, HNSW_UPDATE_ENTRY_ALWAYS, buildstate->entryPoint, insertPage, forkNum, true);
+	HnswUpdateMetaPage(index, HNSW_UPDATE_ENTRY_ALWAYS, buildstate->graph->entryPoint, insertPage, forkNum, true);
 
 	pfree(etup);
 	pfree(ntup);
@@ -222,15 +227,15 @@ CreateNeighborPages(HnswBuildState * buildstate)
 	Relation	index = buildstate->index;
 	ForkNumber	forkNum = buildstate->forkNum;
 	int			m = buildstate->m;
-	ListCell   *lc;
+	slist_iter	iter;
 	HnswNeighborTuple ntup;
 
 	/* Allocate once */
 	ntup = palloc0(BLCKSZ);
 
-	foreach(lc, buildstate->elements)
+	slist_foreach(iter, &buildstate->graph->elements)
 	{
-		HnswElement e = lfirst(lc);
+		HnswElement e = slist_container(HnswElementData, next, iter.cur);
 		Buffer		buf;
 		Page		page;
 		Size		ntupSize = HNSW_NEIGHBOR_TUPLE_SIZE(e->level, m);
@@ -249,25 +254,30 @@ CreateNeighborPages(HnswBuildState * buildstate)
 			elog(ERROR, "failed to add index item to \"%s\"", RelationGetRelationName(index));
 
 		/* Commit */
+		MarkBufferDirty(buf);
 		UnlockReleaseBuffer(buf);
 	}
 
 	pfree(ntup);
 }
 
+#ifdef HNSW_MEMORY
 /*
- * Free elements
+ * Show memory usage
  */
 static void
-FreeElements(HnswBuildState * buildstate)
+ShowMemoryUsage(HnswBuildState * buildstate)
 {
-	ListCell   *lc;
+#if PG_VERSION_NUM >= 130000
-
+	elog(INFO, "graph memory: %zu MB, total memory: %zu MB",
-	foreach(lc, buildstate->elements)
+		 MemoryContextMemAllocated(buildstate->graphCtx, false) / (1024 * 1024),
-		HnswFreeElement(lfirst(lc));
+		 MemoryContextMemAllocated(CurrentMemoryContext, true) / (1024 * 1024));
-
+#else
-	list_free(buildstate->elements);
+	MemoryContextStats(CurrentMemoryContext);
+	elog(INFO, "estimated memory: %zu MB", buildstate->memoryUsed / (1024 * 1024));
+#endif
 }
+#endif
 
 /*
  * Flush pages
@@ -275,26 +285,78 @@ FreeElements(HnswBuildState * buildstate)
 static void
 FlushPages(HnswBuildState * buildstate)
 {
+#ifdef HNSW_MEMORY
+	ShowMemoryUsage(buildstate);
+#endif
+
 	CreateMetaPage(buildstate);
 	CreateElementPages(buildstate);
 	CreateNeighborPages(buildstate);
 
-	buildstate->flushed = true;
+	buildstate->graph->flushed = true;
-	FreeElements(buildstate);
+	MemoryContextReset(buildstate->graphCtx);
+}
+
+#if PG_VERSION_NUM < 130000
+/*
+ * Get the memory used by an element
+ */
+static long
+HnswElementMemory(HnswElement e, int m)
+{
+	long		elementSize = sizeof(HnswElementData);
+
+	elementSize += sizeof(HnswNeighborArray) * (e->level + 1);
+	elementSize += sizeof(HnswCandidate) * (m * (e->level + 2));
+	elementSize += VARSIZE_ANY(DatumGetPointer(e->value));
+	/* Each allocation has a chunk header */
+	elementSize += (e->level + 4) * GENERATIONCHUNK_RAWSIZE;
+	/* Add an extra 5% for alignment and other overhead */
+	return elementSize * 1.05;
+}
+#endif
+
+/*
+ * Find duplicate element
+ */
+static bool
+HnswFindDuplicateInMemory(HnswElement element)
+{
+	HnswNeighborArray *neighbors = HnswGetNeighbors(element, 0);
+
+	for (int i = 0; i < neighbors->length; i++)
+	{
+		HnswCandidate *neighbor = &neighbors->items[i];
+
+		/* Exit early since ordered by distance */
+		if (!datumIsEqual(element->value, neighbor->element->value, false, -1))
+			return false;
+
+		/* Check for space */
+		if (neighbor->element->heaptidsLength < HNSW_HEAPTIDS)
+		{
+			HnswAddHeapTid(neighbor->element, &element->heaptids[0]);
+			return true;
+		}
+	}
+
+	return false;
 }
 
 /*
- * Insert tuple
+ * Insert tuple into in-memory graph
  */
 static bool
-InsertTuple(Relation index, Datum *values, HnswElement element, HnswBuildState * buildstate, HnswElement * dup, MemoryContext outerCtx)
+InsertTupleInMemory(Relation index, Datum *values, ItemPointer heaptid, HnswBuildState * buildstate)
 {
 	FmgrInfo   *procinfo = buildstate->procinfo;
 	Oid			collation = buildstate->collation;
-	HnswElement entryPoint = buildstate->entryPoint;
+	HnswGraph  *graph = buildstate->graph;
+	HnswElement entryPoint = graph->entryPoint;
 	int			efConstruction = buildstate->efConstruction;
 	int			m = buildstate->m;
 	MemoryContext oldCtx;
+	HnswElement element;
 
 	/* Detoast once for all calls */
 	Datum		value = PointerGetDatum(PG_DETOAST_DATUM(values[0]));
@@ -306,52 +368,67 @@ InsertTuple(Relation index, Datum *values, HnswElement element, HnswBuildState *
 			return false;
 	}
 
-	/* Copy value to element so accessible outside of memory context */
+	/* Allocate element in graph memory context */
-	oldCtx = MemoryContextSwitchTo(outerCtx);
+	oldCtx = MemoryContextSwitchTo(buildstate->graphCtx);
+	element = HnswInitElement(heaptid, buildstate->m, buildstate->ml, buildstate->maxLevel);
 	element->value = datumCopy(value, false, -1);
 	MemoryContextSwitchTo(oldCtx);
 
+	/* Update memory usage */
+#if PG_VERSION_NUM >= 130000
+	graph->memoryUsed = MemoryContextMemAllocated(buildstate->graphCtx, false);
+#else
+	graph->memoryUsed += HnswElementMemory(element, buildstate->m);
+#endif
+
 	/* Insert element in graph */
 	HnswInsertElement(element, entryPoint, NULL, procinfo, collation, m, efConstruction, false);
 
 	/* Look for duplicate */
-	*dup = HnswFindDuplicate(element);
+	if (HnswFindDuplicateInMemory(element))
-
-	/* Update neighbors if needed */
-	if (*dup == NULL)
 	{
-		for (int lc = element->level; lc >= 0; lc--)
+		/* No need to free element since memory unlikely to be reallocated */
-		{
+		return true;
-			int			lm = HnswGetLayerM(m, lc);
+	}
-			HnswNeighborArray *neighbors = &element->neighbors[lc];
 
-			for (int i = 0; i < neighbors->length; i++)
+	/* Add element */
-				HnswUpdateConnection(element, &neighbors->items[i], lm, lc, NULL, NULL, procinfo, collation);
+	slist_push_head(&graph->elements, &element->next);
-		}
+
+	/* Update neighbors */
+	for (int lc = element->level; lc >= 0; lc--)
+	{
+		int			lm = HnswGetLayerM(m, lc);
+		HnswNeighborArray *neighbors = HnswGetNeighbors(element, lc);
+
+		for (int i = 0; i < neighbors->length; i++)
+			HnswUpdateConnection(element, &neighbors->items[i], lm, lc, NULL, NULL, procinfo, collation);
 	}
 
 	/* Update entry point if needed */
-	if (*dup == NULL && (entryPoint == NULL || element->level > entryPoint->level))
+	if (entryPoint == NULL || element->level > entryPoint->level)
-		buildstate->entryPoint = element;
+		graph->entryPoint = element;
 
-	UpdateProgress(PROGRESS_CREATEIDX_TUPLES_DONE, ++buildstate->indtuples);
+	return true;
-
-	return *dup == NULL;
 }
 
 /*
- * Get the memory used by an element
+ * Acquire a lock if needed
  */
-static long
+static inline void
-HnswElementMemory(HnswElement e, int m)
+HnswLockAcquire(HnswShared * hnswshared)
 {
-	long		elementSize = sizeof(HnswElementData);
+	if (hnswshared)
+		SpinLockAcquire(&hnswshared->mutex);
+}
 
-	elementSize += sizeof(HnswNeighborArray) * (e->level + 1);
+/*
-	elementSize += sizeof(HnswCandidate) * (m * (e->level + 2));
+ * Release a lock if needed
-	elementSize += sizeof(ItemPointerData);
+ */
-	elementSize += VARSIZE_ANY(DatumGetPointer(e->value));
+static inline void
-	return elementSize;
+HnswLockRelease(HnswShared * hnswshared)
+{
+	if (hnswshared)
+		SpinLockRelease(&hnswshared->mutex);
 }
 
 /*
@@ -362,9 +439,9 @@ BuildCallback(Relation index, CALLBACK_ITEM_POINTER, Datum *values,
 			  bool *isnull, bool tupleIsAlive, void *state)
 {
 	HnswBuildState *buildstate = (HnswBuildState *) state;
+	HnswGraph  *graph = buildstate->graph;
+	HnswShared *hnswshared = buildstate->hnswshared;
 	MemoryContext oldCtx;
-	HnswElement element;
-	HnswElement dup = NULL;
 	bool		inserted;
 
 #if PG_VERSION_NUM < 130000
@@ -375,70 +452,50 @@ BuildCallback(Relation index, CALLBACK_ITEM_POINTER, Datum *values,
 	if (isnull[0])
 		return;
 
-	if (buildstate->flushed || buildstate->memoryLeft <= 0 || list_length(buildstate->elements) == LIST_MAX_LENGTH)
+	/* Flush pages if needed */
+	if (!graph->flushed && graph->memoryUsed >= graph->memoryTotal)
 	{
-		if (!buildstate->flushed)
+		ereport(NOTICE,
-		{
+				(errmsg("hnsw graph no longer fits into maintenance_work_mem after " INT64_FORMAT " tuples", (int64) graph->indtuples),
-			if (buildstate->memoryLeft <= 0)
+				 errdetail("Building will take significantly more time."),
-				ereport(NOTICE,
+				 errhint("Increase maintenance_work_mem to speed up builds.")));
-						(errmsg("hnsw graph no longer fits into maintenance_work_mem after " INT64_FORMAT " tuples", (int64) buildstate->indtuples),
-						 errdetail("Building will take significantly more time."),
-						 errhint("Increase maintenance_work_mem to speed up builds.")));
 
-			FlushPages(buildstate);
+		FlushPages(buildstate);
-		}
-
-		oldCtx = MemoryContextSwitchTo(buildstate->tmpCtx);
-
-		if (HnswInsertTuple(buildstate->index, values, isnull, tid, buildstate->heap, true))
-		{
-			if (buildstate->hnswshared)
-			{
-				HnswShared *hnswshared = buildstate->hnswshared;
-
-				SpinLockAcquire(&hnswshared->mutex);
-				UpdateProgress(PROGRESS_CREATEIDX_TUPLES_DONE, ++hnswshared->indtuples);
-				SpinLockRelease(&hnswshared->mutex);
-			}
-			else
-				UpdateProgress(PROGRESS_CREATEIDX_TUPLES_DONE, ++buildstate->indtuples);
-		}
-
-		/* Reset memory context */
-		MemoryContextSwitchTo(oldCtx);
-		MemoryContextReset(buildstate->tmpCtx);
-
-		return;
 	}
 
-	/* Allocate necessary memory outside of memory context */
-	element = HnswInitElement(tid, buildstate->m, buildstate->ml, buildstate->maxLevel);
-
-	/* Use memory context since detoast can allocate */
 	oldCtx = MemoryContextSwitchTo(buildstate->tmpCtx);
 
 	/* Insert tuple */
-	inserted = InsertTuple(index, values, element, buildstate, &dup, oldCtx);
+	if (graph->flushed)
+		inserted = HnswInsertTuple(index, values, isnull, tid, buildstate->heap, true);
+	else
+		inserted = InsertTupleInMemory(index, values, tid, buildstate);
+
+	/* Update progress */
+	if (inserted)
+	{
+		HnswLockAcquire(hnswshared);
+		UpdateProgress(PROGRESS_CREATEIDX_TUPLES_DONE, ++graph->indtuples);
+		HnswLockRelease(hnswshared);
+	}
 
 	/* Reset memory context */
 	MemoryContextSwitchTo(oldCtx);
 	MemoryContextReset(buildstate->tmpCtx);
+}
 
-	/* Add outside memory context */
+/*
-	if (dup != NULL)
+ * Initialize the graph
-	{
+ */
-		HnswAddHeapTid(dup, tid);
+static void
-		buildstate->memoryLeft -= sizeof(ItemPointerData);
+InitGraph(HnswGraph * graph)
-	}
+{
-
+	slist_init(&graph->elements);
-	/* Add to buildstate or free */
+	graph->entryPoint = NULL;
-	if (inserted)
+	graph->memoryUsed = 0;
-	{
+	graph->memoryTotal = maintenance_work_mem * 1024L;
-		buildstate->elements = lappend(buildstate->elements, element);
+	graph->flushed = false;
-		buildstate->memoryLeft -= HnswElementMemory(element, buildstate->m);
+	graph->indtuples = 0;
-	}
-	else
-		HnswFreeElement(element);
 }
 
 /*
@@ -474,16 +531,20 @@ InitBuildState(HnswBuildState * buildstate, Relation heap, Relation index, Index
 	buildstate->normprocinfo = HnswOptionalProcInfo(index, HNSW_NORM_PROC);
 	buildstate->collation = index->rd_indcollation[0];
 
-	buildstate->elements = NIL;
+	InitGraph(&buildstate->graphData);
-	buildstate->entryPoint = NULL;
+	buildstate->graph = &buildstate->graphData;
 	buildstate->ml = HnswGetMl(buildstate->m);
 	buildstate->maxLevel = HnswGetMaxLevel(buildstate->m);
-	buildstate->memoryLeft = maintenance_work_mem * 1024L;
-	buildstate->flushed = false;
 
 	/* Reuse for each tuple */
 	buildstate->normvec = InitVector(buildstate->dimensions);
 
+	buildstate->graphCtx = GenerationContextCreate(CurrentMemoryContext,
+												   "Hnsw build graph context",
+#if PG_VERSION_NUM >= 150000
+												   1024 * 1024, 1024 * 1024,
+#endif
+												   1024 * 1024);
 	buildstate->tmpCtx = AllocSetContextCreate(CurrentMemoryContext,
 											   "Hnsw build temporary context",
 											   ALLOCSET_DEFAULT_SIZES);
@@ -499,6 +560,7 @@ static void
 FreeBuildState(HnswBuildState * buildstate)
 {
 	pfree(buildstate->normvec);
+	MemoryContextDelete(buildstate->graphCtx);
 	MemoryContextDelete(buildstate->tmpCtx);
 }
 
@@ -518,7 +580,7 @@ ParallelHeapScan(HnswBuildState * buildstate)
 		SpinLockAcquire(&hnswshared->mutex);
 		if (hnswshared->nparticipantsdone == nparticipanttuplesorts)
 		{
-			buildstate->indtuples = hnswshared->indtuples;
+			buildstate->graph = &hnswshared->graphData;
 			reltuples = hnswshared->reltuples;
 			SpinLockRelease(&hnswshared->mutex);
 			break;
@@ -553,9 +615,7 @@ HnswParallelScanAndInsert(HnswSpool * hnswspool, HnswShared * hnswshared, bool p
 	indexInfo = BuildIndexInfo(hnswspool->index);
 	indexInfo->ii_Concurrent = hnswshared->isconcurrent;
 	InitBuildState(&buildstate, hnswspool->heap, hnswspool->index, indexInfo, MAIN_FORKNUM);
-	/* TODO Support in-memory builds */
+	buildstate.graph = &hnswshared->graphData;
-	buildstate.memoryLeft = 0;
-	buildstate.flushed = true;
 	buildstate.hnswshared = hnswshared;
 #if PG_VERSION_NUM >= 120000
 	scan = table_beginscan_parallel(hnswspool->heap,
@@ -780,7 +840,10 @@ HnswBeginParallel(HnswBuildState * buildstate, bool isconcurrent, int request)
 	/* Initialize mutable state */
 	hnswshared->nparticipantsdone = 0;
 	hnswshared->reltuples = 0;
-	hnswshared->indtuples = 0;
+	InitGraph(&hnswshared->graphData);
+	/* TODO Support in-memory builds */
+	hnswshared->graphData.memoryTotal = 0;
+	hnswshared->graphData.flushed = true;
 #if PG_VERSION_NUM >= 120000
 	table_parallelscan_initialize(buildstate->heap,
 								  ParallelTableScanFromHnswShared(hnswshared),
@@ -831,6 +894,27 @@ HnswBeginParallel(HnswBuildState * buildstate, bool isconcurrent, int request)
 	WaitForParallelWorkersToAttach(pcxt);
 }
 
+/*
+ * Compute parallel workers
+ */
+static int
+ComputeParallelWorkers(Relation heap, Relation index)
+{
+	int			parallel_workers;
+
+	/* Make sure it's safe to use parallel workers */
+	parallel_workers = plan_create_index_workers(RelationGetRelid(heap), RelationGetRelid(index));
+	if (parallel_workers == 0)
+		return 0;
+
+	/* Use parallel_workers storage parameter on table if set */
+	parallel_workers = RelationGetParallelWorkers(heap, -1);
+	if (parallel_workers != -1)
+		return Min(parallel_workers, max_parallel_maintenance_workers);
+
+	return max_parallel_maintenance_workers;
+}
+
 /*
  * Build graph
  */
@@ -842,8 +926,8 @@ BuildGraph(HnswBuildState * buildstate, ForkNumber forkNum)
 	UpdateProgress(PROGRESS_CREATEIDX_SUBPHASE, PROGRESS_HNSW_PHASE_LOAD);
 
 	/* Calculate parallel workers */
-	if (hnsw_enable_parallel_build)
+	if (buildstate->heap != NULL && hnsw_enable_parallel_build)
-		parallel_workers = plan_create_index_workers(RelationGetRelid(buildstate->heap), RelationGetRelid(buildstate->index));
+		parallel_workers = ComputeParallelWorkers(buildstate->heap, buildstate->index);
 
 	/* Attempt to launch parallel worker scan when required */
 	if (parallel_workers > 0)
@@ -853,20 +937,29 @@ BuildGraph(HnswBuildState * buildstate, ForkNumber forkNum)
 		HnswBeginParallel(buildstate, buildstate->indexInfo->ii_Concurrent, parallel_workers);
 	}
 
-	/* Add tuples to sort */
+	/* Add tuples to graph */
-	if (buildstate->hnswleader)
+	if (buildstate->heap != NULL)
-		buildstate->reltuples = ParallelHeapScan(buildstate);
-	else
 	{
+		if (buildstate->hnswleader)
+			buildstate->reltuples = ParallelHeapScan(buildstate);
+		else
+		{
 #if PG_VERSION_NUM >= 120000
-		buildstate->reltuples = table_index_build_scan(buildstate->heap, buildstate->index, buildstate->indexInfo,
+			buildstate->reltuples = table_index_build_scan(buildstate->heap, buildstate->index, buildstate->indexInfo,
-													   true, true, BuildCallback, (void *) buildstate, NULL);
+														   true, true, BuildCallback, (void *) buildstate, NULL);
 #else
-		buildstate->reltuples = IndexBuildHeapScan(buildstate->heap, buildstate->index, buildstate->indexInfo,
+			buildstate->reltuples = IndexBuildHeapScan(buildstate->heap, buildstate->index, buildstate->indexInfo,
-												   true, BuildCallback, (void *) buildstate, NULL);
+													   true, BuildCallback, (void *) buildstate, NULL);
 #endif
+		}
+
+		buildstate->indtuples = buildstate->graph->indtuples;
 	}
 
+	/* Flush pages */
+	if (!buildstate->graph->flushed)
+		FlushPages(buildstate);
+
 	/* End parallel build */
 	if (buildstate->hnswleader)
 		HnswEndParallel(buildstate->hnswleader);
@@ -895,13 +988,13 @@ static void
 BuildIndex(Relation heap, Relation index, IndexInfo *indexInfo,
 		   HnswBuildState * buildstate, ForkNumber forkNum)
 {
+#ifdef HNSW_MEMORY
+	SeedRandom(42);
+#endif
+
 	InitBuildState(buildstate, heap, index, indexInfo, forkNum);
 
-	if (buildstate->heap != NULL)
+	BuildGraph(buildstate, forkNum);
-		BuildGraph(buildstate, forkNum);
-
-	if (!buildstate->flushed)
-		FlushPages(buildstate);
 
 	if (RelationNeedsWAL(index))
 		log_newpage_range(index, forkNum, 0, RelationGetNumberOfBlocks(index), true);

src/hnswinsert.c

@@ -5,6 +5,7 @@
 #include "hnsw.h"
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
+#include "utils/datum.h"
 #include "utils/memutils.h"
 
 /*
@@ -219,7 +220,9 @@ WriteNewElementPages(Relation index, HnswElement e, int m, BlockNumber insertPag
 			HnswInsertAppendPage(index, &newbuf, &newpage, state, page, building);
 
 			/* Commit */
-			if (!building)
+			if (building)
+				MarkBufferDirty(buf);
+			else
 				GenericXLogFinish(state);
 
 			/* Unlock previous buffer */
@@ -294,7 +297,13 @@ WriteNewElementPages(Relation index, HnswElement e, int m, BlockNumber insertPag
 	}
 
 	/* Commit */
-	if (!building)
+	if (building)
+	{
+		MarkBufferDirty(buf);
+		if (nbuf != buf)
+			MarkBufferDirty(nbuf);
+	}
+	else
 		GenericXLogFinish(state);
 	UnlockReleaseBuffer(buf);
 	if (nbuf != buf)
@@ -334,7 +343,7 @@ HnswUpdateNeighborPages(Relation index, FmgrInfo *procinfo, Oid collation, HnswE
 	for (int lc = e->level; lc >= 0; lc--)
 	{
 		int			lm = HnswGetLayerM(m, lc);
-		HnswNeighborArray *neighbors = &e->neighbors[lc];
+		HnswNeighborArray *neighbors = HnswGetNeighbors(e, lc);
 
 		for (int i = 0; i < neighbors->length; i++)
 		{
@@ -421,7 +430,9 @@ HnswUpdateNeighborPages(Relation index, FmgrInfo *procinfo, Oid collation, HnswE
 					elog(ERROR, "failed to add index item to \"%s\"", RelationGetRelationName(index));
 
 				/* Commit */
-				if (!building)
+				if (building)
+					MarkBufferDirty(buf);
+				else
 					GenericXLogFinish(state);
 			}
 			else if (!building)
@@ -480,34 +491,56 @@ HnswAddDuplicate(Relation index, HnswElement element, HnswElement dup, bool buil
 	}
 
 	/* Add heap TID */
-	etup->heaptids[i] = *((ItemPointer) linitial(element->heaptids));
+	etup->heaptids[i] = element->heaptids[0];
 
 	/* Overwrite tuple */
 	if (!PageIndexTupleOverwrite(page, dup->offno, (Item) etup, etupSize))
 		elog(ERROR, "failed to add index item to \"%s\"", RelationGetRelationName(index));
 
 	/* Commit */
-	if (!building)
+	if (building)
+		MarkBufferDirty(buf);
+	else
 		GenericXLogFinish(state);
 	UnlockReleaseBuffer(buf);
 
 	return true;
 }
 
+/*
+ * Find duplicate element
+ */
+static bool
+HnswFindDuplicate(Relation index, HnswElement element, bool building)
+{
+	HnswNeighborArray *neighbors = HnswGetNeighbors(element, 0);
+
+	for (int i = 0; i < neighbors->length; i++)
+	{
+		HnswCandidate *neighbor = &neighbors->items[i];
+
+		/* Exit early since ordered by distance */
+		if (!datumIsEqual(element->value, neighbor->element->value, false, -1))
+			return false;
+
+		if (HnswAddDuplicate(index, element, neighbor->element, building))
+			return true;
+	}
+
+	return false;
+}
+
 /*
  * Write changes to disk
  */
 static void
-WriteElement(Relation index, FmgrInfo *procinfo, Oid collation, HnswElement element, int m, int efConstruction, HnswElement dup, HnswElement entryPoint, bool building)
+WriteElement(Relation index, FmgrInfo *procinfo, Oid collation, HnswElement element, int m, int efConstruction, HnswElement entryPoint, bool building)
 {
 	BlockNumber newInsertPage = InvalidBlockNumber;
 
-	/* Try to add to existing page */
+	/* Look for duplicate */
-	if (dup != NULL)
+	if (HnswFindDuplicate(index, element, building))
-	{
+		return;
-		if (HnswAddDuplicate(index, element, dup, building))
-			return;
-	}
 
 	/* Write element and neighbor tuples */
 	WriteNewElementPages(index, element, m, GetInsertPage(index), &newInsertPage, building);
@@ -519,7 +552,7 @@ WriteElement(Relation index, FmgrInfo *procinfo, Oid collation, HnswElement elem
 	/* Update neighbors */
 	HnswUpdateNeighborPages(index, procinfo, collation, element, m, false, building);
 
-	/* Update metapage if needed */
+	/* Update entry point if needed */
 	if (entryPoint == NULL || element->level > entryPoint->level)
 		HnswUpdateMetaPage(index, HNSW_UPDATE_ENTRY_GREATER, element, InvalidBlockNumber, MAIN_FORKNUM, building);
 }
@@ -538,7 +571,6 @@ HnswInsertTuple(Relation index, Datum *values, bool *isnull, ItemPointer heap_ti
 	int			efConstruction = HnswGetEfConstruction(index);
 	FmgrInfo   *procinfo = index_getprocinfo(index, 1, HNSW_DISTANCE_PROC);
 	Oid			collation = index->rd_indcollation[0];
-	HnswElement dup;
 	LOCKMODE	lockmode = ShareLock;
 
 	/* Detoast once for all calls */
@@ -583,11 +615,8 @@ HnswInsertTuple(Relation index, Datum *values, bool *isnull, ItemPointer heap_ti
 	/* Insert element in graph */
 	HnswInsertElement(element, entryPoint, index, procinfo, collation, m, efConstruction, false);
 
-	/* Look for duplicate */
-	dup = HnswFindDuplicate(element);
-
 	/* Write to disk */
-	WriteElement(index, procinfo, collation, element, m, efConstruction, dup, entryPoint, building);
+	WriteElement(index, procinfo, collation, element, m, efConstruction, entryPoint, building);
 
 	/* Release lock */
 	UnlockPage(index, HNSW_UPDATE_LOCK, lockmode);

src/hnswscan.c

@@ -188,15 +188,13 @@ hnswgettuple(IndexScanDesc scan, ScanDirection dir)
 		ItemPointer heaptid;
 
 		/* Move to next element if no valid heap TIDs */
-		if (list_length(hc->element->heaptids) == 0)
+		if (hc->element->heaptidsLength == 0)
 		{
 			so->w = list_delete_last(so->w);
 			continue;
 		}
 
-		heaptid = llast(hc->element->heaptids);
+		heaptid = &hc->element->heaptids[--hc->element->heaptidsLength];
-
-		hc->element->heaptids = list_delete_last(hc->element->heaptids);
 
 		MemoryContextSwitchTo(oldCtx);
 

src/hnswutils.c

@@ -206,17 +206,6 @@ HnswInitNeighbors(HnswElement element, int m)
 	}
 }
 
-/*
- * Free neighbors
- */
-static void
-HnswFreeNeighbors(HnswElement element)
-{
-	for (int lc = 0; lc <= element->level; lc++)
-		pfree(element->neighbors[lc].items);
-	pfree(element->neighbors);
-}
-
 /*
  * Allocate an element
  */
@@ -231,7 +220,7 @@ HnswInitElement(ItemPointer heaptid, int m, double ml, int maxLevel)
 	if (level > maxLevel)
 		level = maxLevel;
 
-	element->heaptids = NIL;
+	element->heaptidsLength = 0;
 	HnswAddHeapTid(element, heaptid);
 
 	element->level = level;
@@ -244,29 +233,13 @@ HnswInitElement(ItemPointer heaptid, int m, double ml, int maxLevel)
 	return element;
 }
 
-/*
- * Free an element
- */
-void
-HnswFreeElement(HnswElement element)
-{
-	HnswFreeNeighbors(element);
-	list_free_deep(element->heaptids);
-	if (DatumGetPointer(element->value))
-		pfree(DatumGetPointer(element->value));
-	pfree(element);
-}
-
 /*
  * Add a heap TID to an element
  */
 void
 HnswAddHeapTid(HnswElement element, ItemPointer heaptid)
 {
-	ItemPointer copy = palloc(sizeof(ItemPointerData));
+	element->heaptids[element->heaptidsLength++] = *heaptid;
-
-	ItemPointerCopy(heaptid, copy);
-	element->heaptids = lappend(element->heaptids, copy);
 }
 
 /*
@@ -379,7 +352,9 @@ HnswUpdateMetaPage(Relation index, int updateEntry, HnswElement entryPoint, Bloc
 
 	HnswUpdateMetaPageInfo(page, updateEntry, entryPoint, insertPage);
 
-	if (!building)
+	if (building)
+		MarkBufferDirty(buf);
+	else
 		GenericXLogFinish(state);
 	UnlockReleaseBuffer(buf);
 }
@@ -395,8 +370,8 @@ HnswSetElementTuple(HnswElementTuple etup, HnswElement element)
 	etup->deleted = 0;
 	for (int i = 0; i < HNSW_HEAPTIDS; i++)
 	{
-		if (i < list_length(element->heaptids))
+		if (i < element->heaptidsLength)
-			etup->heaptids[i] = *((ItemPointer) list_nth(element->heaptids, i));
+			etup->heaptids[i] = element->heaptids[i];
 		else
 			ItemPointerSetInvalid(&etup->heaptids[i]);
 	}
@@ -415,7 +390,7 @@ HnswSetNeighborTuple(HnswNeighborTuple ntup, HnswElement e, int m)
 
 	for (int lc = e->level; lc >= 0; lc--)
 	{
-		HnswNeighborArray *neighbors = &e->neighbors[lc];
+		HnswNeighborArray *neighbors = HnswGetNeighbors(e, lc);
 		int			lm = HnswGetLayerM(m, lc);
 
 		for (int i = 0; i < lm; i++)
@@ -473,7 +448,7 @@ LoadNeighborsFromPage(HnswElement element, Relation index, Page page, int m)
 		if (level < 0)
 			level = 0;
 
-		neighbors = &element->neighbors[level];
+		neighbors = HnswGetNeighbors(element, level);
 		hc = &neighbors->items[neighbors->length++];
 		hc->element = e;
 	}
@@ -507,7 +482,7 @@ HnswLoadElementFromTuple(HnswElement element, HnswElementTuple etup, bool loadHe
 	element->deleted = etup->deleted;
 	element->neighborPage = ItemPointerGetBlockNumber(&etup->neighbortid);
 	element->neighborOffno = ItemPointerGetOffsetNumber(&etup->neighbortid);
-	element->heaptids = NIL;
+	element->heaptidsLength = 0;
 
 	if (loadHeaptids)
 	{
@@ -650,13 +625,12 @@ AddToVisited(visited_hash v, HnswCandidate * hc, Relation index, bool *found)
 List *
 HnswSearchLayer(Datum q, List *ep, int ef, int lc, Relation index, FmgrInfo *procinfo, Oid collation, int m, bool inserting, HnswElement skipElement)
 {
-	ListCell   *lc2;
-
 	List	   *w = NIL;
 	pairingheap *C = pairingheap_allocate(CompareNearestCandidates, NULL);
 	pairingheap *W = pairingheap_allocate(CompareFurthestCandidates, NULL);
 	int			wlen = 0;
 	visited_hash v;
+	ListCell   *lc2;
 
 	/* Create hash table */
 	if (index == NULL)
@@ -680,7 +654,7 @@ HnswSearchLayer(Datum q, List *ep, int ef, int lc, Relation index, FmgrInfo *pro
 		 * would be ideal to do this for inserts as well, but this could
 		 * affect insert performance.
 		 */
-		if (skipElement == NULL || list_length(hc->element->heaptids) != 0)
+		if (skipElement == NULL || hc->element->heaptidsLength != 0)
 			wlen++;
 	}
 
@@ -697,7 +671,7 @@ HnswSearchLayer(Datum q, List *ep, int ef, int lc, Relation index, FmgrInfo *pro
 			HnswLoadNeighbors(c->element, index, m);
 
 		/* Get the neighborhood at layer lc */
-		neighborhood = &c->element->neighbors[lc];
+		neighborhood = HnswGetNeighbors(c->element, lc);
 
 		for (int i = 0; i < neighborhood->length; i++)
 		{
@@ -739,7 +713,7 @@ HnswSearchLayer(Datum q, List *ep, int ef, int lc, Relation index, FmgrInfo *pro
 					 * vacuuming. It would be ideal to do this for inserts as
 					 * well, but this could affect insert performance.
 					 */
-					if (skipElement == NULL || list_length(e->element->heaptids) != 0)
+					if (skipElement == NULL || e->element->heaptidsLength != 0)
 					{
 						wlen++;
 
@@ -800,23 +774,23 @@ HnswGetDistance(HnswElement a, HnswElement b, int lc, FmgrInfo *procinfo, Oid co
 	/* Look for cached distance */
 	if (a->neighbors != NULL)
 	{
-		Assert(a->level >= lc);
+		HnswNeighborArray *neighbors = HnswGetNeighbors(a, lc);
 
-		for (int i = 0; i < a->neighbors[lc].length; i++)
+		for (int i = 0; i < neighbors->length; i++)
 		{
-			if (a->neighbors[lc].items[i].element == b)
+			if (neighbors->items[i].element == b)
-				return a->neighbors[lc].items[i].distance;
+				return neighbors->items[i].distance;
 		}
 	}
 
 	if (b->neighbors != NULL)
 	{
-		Assert(b->level >= lc);
+		HnswNeighborArray *neighbors = HnswGetNeighbors(b, lc);
 
-		for (int i = 0; i < b->neighbors[lc].length; i++)
+		for (int i = 0; i < neighbors->length; i++)
 		{
-			if (b->neighbors[lc].items[i].element == a)
+			if (neighbors->items[i].element == a)
-				return b->neighbors[lc].items[i].distance;
+				return neighbors->items[i].distance;
 		}
 	}
 
@@ -852,7 +826,8 @@ SelectNeighbors(List *c, int m, int lc, FmgrInfo *procinfo, Oid collation, HnswE
 	List	   *r = NIL;
 	List	   *w = list_copy(c);
 	pairingheap *wd;
-	bool		mustCalculate = !e2->neighbors[lc].closerSet;
+	HnswNeighborArray *neighbors = HnswGetNeighbors(e2, lc);
+	bool		mustCalculate = !neighbors->closerSet;
 	List	   *added = NIL;
 	bool		removedAny = false;
 
@@ -916,7 +891,7 @@ SelectNeighbors(List *c, int m, int lc, FmgrInfo *procinfo, Oid collation, HnswE
 	}
 
 	/* Cached value can only be used in future if sorted deterministically */
-	e2->neighbors[lc].closerSet = sortCandidates;
+	neighbors->closerSet = sortCandidates;
 
 	/* Keep pruned connections */
 	while (!pairingheap_is_empty(wd) && list_length(r) < m)
@@ -934,30 +909,6 @@ SelectNeighbors(List *c, int m, int lc, FmgrInfo *procinfo, Oid collation, HnswE
 	return r;
 }
 
-/*
- * Find duplicate element
- */
-HnswElement
-HnswFindDuplicate(HnswElement e)
-{
-	HnswNeighborArray *neighbors = &e->neighbors[0];
-
-	for (int i = 0; i < neighbors->length; i++)
-	{
-		HnswCandidate *neighbor = &neighbors->items[i];
-
-		/* Exit early since ordered by distance */
-		if (!datumIsEqual(e->value, neighbor->element->value, false, -1))
-			break;
-
-		/* Check for space */
-		if (list_length(neighbor->element->heaptids) < HNSW_HEAPTIDS)
-			return neighbor->element;
-	}
-
-	return NULL;
-}
-
 /*
  * Add connections
  */
@@ -965,7 +916,7 @@ static void
 AddConnections(HnswElement element, List *neighbors, int m, int lc)
 {
 	ListCell   *lc2;
-	HnswNeighborArray *a = &element->neighbors[lc];
+	HnswNeighborArray *a = HnswGetNeighbors(element, lc);
 
 	foreach(lc2, neighbors)
 		a->items[a->length++] = *((HnswCandidate *) lfirst(lc2));
@@ -977,7 +928,7 @@ AddConnections(HnswElement element, List *neighbors, int m, int lc)
 void
 HnswUpdateConnection(HnswElement element, HnswCandidate * hc, int m, int lc, int *updateIdx, Relation index, FmgrInfo *procinfo, Oid collation)
 {
-	HnswNeighborArray *currentNeighbors = &hc->element->neighbors[lc];
+	HnswNeighborArray *currentNeighbors = HnswGetNeighbors(hc->element, lc);
 
 	HnswCandidate hc2;
 
@@ -1012,7 +963,7 @@ HnswUpdateConnection(HnswElement element, HnswCandidate * hc, int m, int lc, int
 					hc3->distance = GetCandidateDistance(hc3, q, procinfo, collation);
 
 				/* Prune element if being deleted */
-				if (list_length(hc3->element->heaptids) == 0)
+				if (hc3->element->heaptidsLength == 0)
 				{
 					pruned = &currentNeighbors->items[i];
 					break;
@@ -1070,7 +1021,7 @@ RemoveElements(List *w, HnswElement skipElement)
 		if (skipElement != NULL && hc->element->blkno == skipElement->blkno && hc->element->offno == skipElement->offno)
 			continue;
 
-		if (list_length(hc->element->heaptids) != 0)
+		if (hc->element->heaptidsLength != 0)
 			w2 = lappend(w2, hc);
 	}
 

src/hnswvacuum.c

@@ -206,7 +206,7 @@ RepairGraphElement(HnswVacuumState * vacuumstate, HnswElement element, HnswEleme
 
 	/* Init fields */
 	HnswInitNeighbors(element, m);
-	element->heaptids = NIL;
+	element->heaptidsLength = 0;
 
 	/* Add element to graph, skipping itself */
 	HnswInsertElement(element, entryPoint, index, procinfo, collation, m, efConstruction, true);

src/ivfbuild.c

@@ -543,10 +543,10 @@ CreateListPages(Relation index, VectorArray centers, int dimensions,
 	pfree(list);
 }
 
+#ifdef IVFFLAT_KMEANS_DEBUG
 /*
  * Print k-means metrics
  */
-#ifdef IVFFLAT_KMEANS_DEBUG
 static void
 PrintKmeansMetrics(IvfflatBuildState * buildstate)
 {

src/ivfflat.c

@@ -105,6 +105,20 @@ ivfflatcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
 	 */
 	costs.numIndexTuples = path->indexinfo->tuples * ratio;
 
+	/*
+	 * Do not use index if no limit or limit + offset > expected tuples unless
+	 * enable_seqscan = off
+	 */
+	if (root->limit_tuples < 0 || root->limit_tuples > costs.numIndexTuples)
+	{
+		*indexStartupCost = 1.0e10 - 1;
+		*indexTotalCost = 1.0e10 - 1;
+		*indexSelectivity = 0;
+		*indexCorrelation = 0;
+		*indexPages = 0;
+		return;
+	}
+
 #if PG_VERSION_NUM >= 120000
 	genericcostestimate(root, path, loop_count, &costs);
 #else

src/ivfkmeans.c

@@ -6,6 +6,10 @@
 #include "ivfflat.h"
 #include "miscadmin.h"
 
+#ifdef IVFFLAT_MEMORY
+#include "utils/memutils.h"
+#endif
+
 /*
  * Initialize with kmeans++
  *
@@ -151,6 +155,23 @@ QuickCenters(Relation index, VectorArray samples, VectorArray centers)
 	}
 }
 
+#ifdef IVFFLAT_MEMORY
+/*
+ * Show memory usage
+ */
+static void
+ShowMemoryUsage(Size estimatedSize)
+{
+#if PG_VERSION_NUM >= 130000
+	elog(INFO, "total memory: %zu MB",
+		 MemoryContextMemAllocated(CurrentMemoryContext, true) / (1024 * 1024));
+#else
+	MemoryContextStats(CurrentMemoryContext);
+#endif
+	elog(INFO, "estimated memory: %zu MB", estimatedSize / (1024 * 1024));
+}
+#endif
+
 /*
  * Use Elkan for performance. This requires distance function to satisfy triangle inequality.
  *
@@ -231,6 +252,10 @@ ElkanKmeans(Relation index, VectorArray samples, VectorArray centers)
 		vec->dim = dimensions;
 	}
 
+#ifdef IVFFLAT_MEMORY
+	ShowMemoryUsage(totalSize);
+#endif
+
 	/* Pick initial centers */
 	InitCenters(index, samples, centers, lowerBound);
 

src/vector.c

@@ -177,14 +177,15 @@ PGDLLEXPORT PG_FUNCTION_INFO_V1(vector_in);
 Datum
 vector_in(PG_FUNCTION_ARGS)
 {
-	char	   *str = PG_GETARG_CSTRING(0);
+	char	   *lit = PG_GETARG_CSTRING(0);
 	int32		typmod = PG_GETARG_INT32(2);
 	float		x[VECTOR_MAX_DIM];
 	int			dim = 0;
 	char	   *pt;
 	char	   *stringEnd;
 	Vector	   *result;
-	char	   *lit = pstrdup(str);
+	char	   *litcopy = pstrdup(lit);
+	char	   *str = litcopy;
 
 	while (vector_isspace(*str))
 		str++;
@@ -268,7 +269,7 @@ vector_in(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_DATA_EXCEPTION),
 				 errmsg("vector must have at least 1 dimension")));
 
-	pfree(lit);
+	pfree(litcopy);
 
 	CheckExpectedDim(typmod, dim);
 

test/t/018_ivfflat_deletes.pl

@@ -1,43 +0,0 @@
-use strict;
-use warnings;
-use PostgresNode;
-use TestLib;
-use Test::More;
-
-my $dim = 3;
-
-my $array_sql = join(",", ('random()') x $dim);
-
-# Initialize node
-my $node = get_new_node('node');
-$node->init;
-$node->start;
-
-# Create table and index
-$node->safe_psql("postgres", "CREATE EXTENSION vector;");
-$node->safe_psql("postgres", "CREATE TABLE tst (i serial, v vector($dim));");
-$node->safe_psql("postgres",
-	"INSERT INTO tst (v) SELECT ARRAY[$array_sql] FROM generate_series(1, 10000) i;"
-);
-$node->safe_psql("postgres", "CREATE INDEX ON tst USING ivfflat (v vector_l2_ops);");
-
-# Delete data
-$node->safe_psql("postgres", "DELETE FROM tst WHERE i % 100 != 0;");
-
-my $exp = $node->safe_psql("postgres", qq(
-	SET enable_indexscan = off;
-	SELECT i FROM tst ORDER BY v <-> '[0,0,0]';
-));
-
-# Run twice to make sure correct tuples marked as dead
-for (1 .. 2)
-{
-	my $res = $node->safe_psql("postgres", qq(
-		SET enable_seqscan = off;
-		SET ivfflat.probes = 100;
-		SELECT i FROM tst ORDER BY v <-> '[0,0,0]';
-	));
-	is($res, $exp);
-}
-
-done_testing();

test/t/019_ivfflat_limit.pl

@@ -0,0 +1,64 @@
+use strict;
+use warnings;
+use PostgresNode;
+use TestLib;
+use Test::More;
+
+# Initialize node
+my $node = get_new_node('node');
+$node->init;
+$node->start;
+
+# Create table and index
+$node->safe_psql("postgres", "CREATE EXTENSION vector;");
+$node->safe_psql("postgres", "CREATE TABLE tst (v vector(3));");
+$node->safe_psql("postgres",
+	"INSERT INTO tst SELECT ARRAY[random(), random(), random()] FROM generate_series(1, 1000) i;"
+);
+$node->safe_psql("postgres", "CREATE INDEX ON tst USING ivfflat (v vector_l2_ops) WITH (lists = 10);");
+
+# Test limit
+my $explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 100;
+));
+like($explain, qr/Index Scan/);
+
+# Test limit with probes
+$explain = $node->safe_psql("postgres", qq(
+	SET ivfflat.probes = 2;
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 200;
+));
+like($explain, qr/Index Scan/);
+
+# Test limit + offset
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 90 OFFSET 10;
+));
+like($explain, qr/Index Scan/);
+
+# Test limit > expected tuples
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 101;
+));
+like($explain, qr/Seq Scan/);
+
+# Test limit > expected tuples with probes
+$explain = $node->safe_psql("postgres", qq(
+	SET ivfflat.probes = 2;
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 201;
+));
+like($explain, qr/Seq Scan/);
+
+# Test limit + offset > expected tuples
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 91 OFFSET 10;
+));
+like($explain, qr/Seq Scan/);
+
+# Test no limit
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]';
+));
+like($explain, qr/Seq Scan/);
+
+done_testing();

test/t/020_hnsw_limit.pl

@@ -0,0 +1,62 @@
+use strict;
+use warnings;
+use PostgresNode;
+use TestLib;
+use Test::More;
+
+# Initialize node
+my $node = get_new_node('node');
+$node->init;
+$node->start;
+
+# Create table and index
+$node->safe_psql("postgres", "CREATE EXTENSION vector;");
+$node->safe_psql("postgres", "CREATE TABLE tst (v vector(3));");
+$node->safe_psql("postgres",
+	"INSERT INTO tst SELECT ARRAY[random(), random(), random()] FROM generate_series(1, 1000) i;"
+);
+$node->safe_psql("postgres", "CREATE INDEX ON tst USING hnsw (v vector_l2_ops);");
+
+# Test limit
+my $explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 40;
+));
+like($explain, qr/Index Scan/);
+
+# Test limit with CTE
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE WITH cte AS (SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 40) SELECT * FROM cte;
+));
+like($explain, qr/Index Scan/);
+
+# Test limit + offset
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 30 OFFSET 10;
+));
+like($explain, qr/Index Scan/);
+
+# Test limit > ef_search
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 41;
+));
+like($explain, qr/Seq Scan/);
+
+# Test limit > ef_search with CTE
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE WITH cte AS (SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 41) SELECT * FROM cte;
+));
+like($explain, qr/Seq Scan/);
+
+# Test limit + offset > ef_search
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 31 OFFSET 10;
+));
+like($explain, qr/Seq Scan/);
+
+# Test no limit
+$explain = $node->safe_psql("postgres", qq(
+	EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]';
+));
+like($explain, qr/Seq Scan/);
+
+done_testing();