v20250303-0004-WIP-parallel-inserts-into-GIN-index.patch

From e21754e663e5bebfe005dd95d8e61184d4e18b05 Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas@vondra.me>
Date: Tue, 25 Feb 2025 16:16:24 +0100
Subject: [PATCH v20250303 4/4] WIP: parallel inserts into GIN index

---
 src/backend/access/gin/gininsert.c            | 450 +++++++++++-------
 .../utils/activity/wait_event_names.txt       |   2 +
 2 files changed, 286 insertions(+), 166 deletions(-)

diff --git a/src/backend/access/gin/gininsert.c b/src/backend/access/gin/gininsert.c
index e873443784a..750c0c3270d 100644
--- a/src/backend/access/gin/gininsert.c
+++ b/src/backend/access/gin/gininsert.c
@@ -26,7 +26,9 @@
 #include "miscadmin.h"
 #include "nodes/execnodes.h"
 #include "pgstat.h"
+#include "storage/barrier.h"
 #include "storage/bufmgr.h"
+#include "storage/buffile.h"
 #include "storage/predicate.h"
 #include "tcop/tcopprot.h"		/* pgrminclude ignore */
 #include "utils/datum.h"
@@ -42,6 +44,11 @@
 #define PARALLEL_KEY_WAL_USAGE			UINT64CONST(0xB000000000000004)
 #define PARALLEL_KEY_BUFFER_USAGE		UINT64CONST(0xB000000000000005)
 
+/* The phases for parallel builds, used by build_barrier. */
+#define GIN_BUILD_INIT					0
+#define GIN_BUILD_SCAN					1
+#define GIN_BUILD_PARTITION				2
+
 /*
  * Status for index builds performed in parallel.  This is allocated in a
  * dynamic shared memory segment.
@@ -88,6 +95,9 @@ typedef struct GinBuildShared
 	double		reltuples;
 	double		indtuples;
 
+	Barrier		build_barrier;
+	SharedFileSet fileset;		/* space for shared temporary files */
+
 	/*
 	 * ParallelTableScanDescData data follows. Can't directly embed here, as
 	 * implementations of the parallel table scan desc interface might need
@@ -173,7 +183,6 @@ static void _gin_begin_parallel(GinBuildState *buildstate, Relation heap, Relati
 static void _gin_end_parallel(GinLeader *ginleader, GinBuildState *state);
 static Size _gin_parallel_estimate_shared(Relation heap, Snapshot snapshot);
 static double _gin_parallel_heapscan(GinBuildState *buildstate);
-static double _gin_parallel_merge(GinBuildState *buildstate);
 static void _gin_leader_participate_as_worker(GinBuildState *buildstate,
 											  Relation heap, Relation index);
 static void _gin_parallel_scan_and_build(GinBuildState *buildstate,
@@ -189,6 +198,12 @@ static GinTuple *_gin_build_tuple(OffsetNumber attrnum, unsigned char category,
 								  Datum key, int16 typlen, bool typbyval,
 								  ItemPointerData *items, uint32 nitems);
 
+static double _gin_partition_sorted_data(GinBuildState *state);
+static void _gin_parallel_insert(GinBuildState *state,
+								 GinBuildShared *gistshared,
+								 Relation heap, Relation index,
+								 bool progress);
+
 /*
  * Adds array of item pointers to tuple's posting list, or
  * creates posting tree and tuple pointing to tree in case
@@ -699,8 +714,12 @@ ginbuild(Relation heap, Relation index, IndexInfo *indexInfo)
 									  maintenance_work_mem, coordinate,
 									  TUPLESORT_NONE);
 
-		/* scan the relation in parallel and merge per-worker results */
-		reltuples = _gin_parallel_merge(state);
+		/* partition the sorted data */
+		reltuples = _gin_partition_sorted_data(state);
+
+		/* do the insert for the leader's partition */
+		_gin_parallel_insert(state, state->bs_leader->ginshared,
+							 heap, index, true);
 
 		_gin_end_parallel(state->bs_leader, state);
 	}
@@ -989,6 +1008,12 @@ _gin_begin_parallel(GinBuildState *buildstate, Relation heap, Relation index,
 	ginshared->reltuples = 0.0;
 	ginshared->indtuples = 0.0;
 
+	/* used to wait for data to insert */
+	BarrierInit(&ginshared->build_barrier, scantuplesortstates);
+
+	/* Set up the space we'll use for shared temporary files. */
+	SharedFileSetInit(&ginshared->fileset, pcxt->seg);
+
 	table_parallelscan_initialize(heap,
 								  ParallelTableScanFromGinBuildShared(ginshared),
 								  snapshot);
@@ -1056,6 +1081,11 @@ _gin_begin_parallel(GinBuildState *buildstate, Relation heap, Relation index,
 	 * sure that the failure-to-start case will not hang forever.
 	 */
 	WaitForParallelWorkersToAttach(pcxt);
+
+	/* wait for workers to read the data and add them to tuplesort */
+	if (BarrierArriveAndWait(&ginshared->build_barrier,
+							 WAIT_EVENT_GIN_BUILD_SCAN))
+		elog(LOG, "data scanned, leader continues");
 }
 
 /*
@@ -1069,6 +1099,8 @@ _gin_end_parallel(GinLeader *ginleader, GinBuildState *state)
 	/* Shutdown worker processes */
 	WaitForParallelWorkersToFinish(ginleader->pcxt);
 
+	SharedFileSetDeleteAll(&ginleader->ginshared->fileset);
+
 	/*
 	 * Next, accumulate WAL usage.  (This must wait for the workers to finish,
 	 * or we might get incomplete data.)
@@ -1713,169 +1745,6 @@ GinBufferCanAddKey(GinBuffer *buffer, GinTuple *tup)
 	return GinBufferKeyEquals(buffer, tup);
 }
 
-/*
- * Within leader, wait for end of heap scan and merge per-worker results.
- *
- * After waiting for all workers to finish, merge the per-worker results into
- * the complete index. The results from each worker are sorted by block number
- * (start of the page range). While combinig the per-worker results we merge
- * summaries for the same page range, and also fill-in empty summaries for
- * ranges without any tuples.
- *
- * Returns the total number of heap tuples scanned.
- */
-static double
-_gin_parallel_merge(GinBuildState *state)
-{
-	GinTuple   *tup;
-	Size		tuplen;
-	double		reltuples = 0;
-	GinBuffer  *buffer;
-
-	/* GIN tuples from workers, merged by leader */
-	double		numtuples = 0;
-
-	/* wait for workers to scan table and produce partial results */
-	reltuples = _gin_parallel_heapscan(state);
-
-	/* Execute the sort */
-	pgstat_progress_update_param(PROGRESS_CREATEIDX_SUBPHASE,
-								 PROGRESS_GIN_PHASE_PERFORMSORT_2);
-
-	/* do the actual sort in the leader */
-	tuplesort_performsort(state->bs_sortstate);
-
-	/*
-	 * Initialize buffer to combine entries for the same key.
-	 *
-	 * The leader is allowed to use the whole maintenance_work_mem buffer to
-	 * combine data. The parallel workers already completed.
-	 */
-	buffer = GinBufferInit(state->ginstate.index);
-
-	/*
-	 * Set the progress target for the next phase.  Reset the block number
-	 * values set by table_index_build_scan
-	 */
-	{
-		const int	progress_index[] = {
-			PROGRESS_CREATEIDX_SUBPHASE,
-			PROGRESS_CREATEIDX_TUPLES_TOTAL,
-			PROGRESS_SCAN_BLOCKS_TOTAL,
-			PROGRESS_SCAN_BLOCKS_DONE
-		};
-		const int64 progress_vals[] = {
-			PROGRESS_GIN_PHASE_MERGE_2,
-			state->bs_numtuples,
-			0, 0
-		};
-
-		pgstat_progress_update_multi_param(4, progress_index, progress_vals);
-	}
-
-	/*
-	 * Read the GIN tuples from the shared tuplesort, sorted by category and
-	 * key. That probably gives us order matching how data is organized in the
-	 * index.
-	 *
-	 * We don't insert the GIN tuples right away, but instead accumulate as
-	 * many TIDs for the same key as possible, and then insert that at once.
-	 * This way we don't need to decompress/recompress the posting lists, etc.
-	 */
-	while ((tup = tuplesort_getgintuple(state->bs_sortstate, &tuplen, true)) != NULL)
-	{
-		CHECK_FOR_INTERRUPTS();
-
-		/*
-		 * If the buffer can accept the new GIN tuple, just store it there and
-		 * we're done. If it's a different key (or maybe too much data) flush
-		 * the current contents into the index first.
-		 */
-		if (!GinBufferCanAddKey(buffer, tup))
-		{
-			/*
-			 * Buffer is not empty and it's storing a different key - flush
-			 * the data into the insert, and start a new entry for current
-			 * GinTuple.
-			 */
-			AssertCheckItemPointers(buffer);
-			Assert(!PointerIsValid(buffer->cached));
-
-			ginEntryInsert(&state->ginstate,
-						   buffer->attnum, buffer->key, buffer->category,
-						   buffer->items, buffer->nitems, &state->buildStats);
-
-			/* discard the existing data */
-			GinBufferReset(buffer);
-		}
-
-		/*
-		 * We're about to add a GIN tuple to the buffer - check the memory
-		 * limit first, and maybe write out some of the data into the index
-		 * first, if needed (and possible). We only flush the part of the TID
-		 * list that we know won't change, and only if there's enough data for
-		 * compression to work well.
-		 */
-		if (GinBufferShouldTrim(buffer, tup))
-		{
-			Assert(buffer->nfrozen > 0);
-
-			/*
-			 * Buffer is not empty and it's storing a different key - flush
-			 * the data into the insert, and start a new entry for current
-			 * GinTuple.
-			 */
-			AssertCheckItemPointers(buffer);
-			Assert(!PointerIsValid(buffer->cached));
-
-			ginEntryInsert(&state->ginstate,
-						   buffer->attnum, buffer->key, buffer->category,
-						   buffer->items, buffer->nfrozen, &state->buildStats);
-
-			/* truncate the data we've just discarded */
-			GinBufferTrim(buffer);
-		}
-
-		/*
-		 * Remember data for the current tuple (either remember the new key,
-		 * or append if to the existing data).
-		 */
-		GinBufferMergeTuple(buffer, tup);
-
-		if (buffer->cached)
-			GinBufferUnpackCached(buffer, 0);
-
-		/* Report progress */
-		pgstat_progress_update_param(PROGRESS_CREATEIDX_TUPLES_DONE,
-									 ++numtuples);
-	}
-
-	/* flush data remaining in the buffer (for the last key) */
-	if (!GinBufferIsEmpty(buffer))
-	{
-		AssertCheckItemPointers(buffer);
-		Assert(!PointerIsValid(buffer->cached));
-
-		ginEntryInsert(&state->ginstate,
-					   buffer->attnum, buffer->key, buffer->category,
-					   buffer->items, buffer->nitems, &state->buildStats);
-
-		/* discard the existing data */
-		GinBufferReset(buffer);
-
-		/* Report progress */
-		pgstat_progress_update_param(PROGRESS_CREATEIDX_TUPLES_DONE,
-									 ++numtuples);
-	}
-
-	/* relase all the memory */
-	GinBufferFree(buffer);
-
-	tuplesort_end(state->bs_sortstate);
-
-	return reltuples;
-}
-
 /*
  * Returns size of shared memory required to store state for a parallel
  * gin index build based on the snapshot its parallel scan will use.
@@ -2093,6 +1962,9 @@ _gin_parallel_build_main(dsm_segment *seg, shm_toc *toc)
 	/* Prepare to track buffer usage during parallel execution */
 	InstrStartParallelQuery();
 
+	/* attach to the fileset too */
+	SharedFileSetAttach(&ginshared->fileset, seg);
+
 	/*
 	 * Might as well use reliable figure when doling out maintenance_work_mem
 	 * (when requested number of workers were not launched, this will be
@@ -2103,6 +1975,20 @@ _gin_parallel_build_main(dsm_segment *seg, shm_toc *toc)
 	_gin_parallel_scan_and_build(&buildstate, ginshared, sharedsort,
 								 heapRel, indexRel, sortmem, false);
 
+	/* wait for workers to read the data and add them to tuplesort */
+	if (BarrierArriveAndWait(&ginshared->build_barrier,
+							 WAIT_EVENT_GIN_BUILD_SCAN))
+		elog(LOG, "data scanned by workers, leader continues");
+
+	/* leader sorts and partitions the data */
+
+	/* wait for the leader to partition the data */
+	if (BarrierArriveAndWait(&ginshared->build_barrier,
+							 WAIT_EVENT_GIN_BUILD_PARTITION))
+		elog(LOG, "data partitioned by leader, worker continues");
+
+	_gin_parallel_insert(&buildstate, ginshared, heapRel, indexRel, false);
+
 	/* Report WAL/buffer usage during parallel execution */
 	bufferusage = shm_toc_lookup(toc, PARALLEL_KEY_BUFFER_USAGE, false);
 	walusage = shm_toc_lookup(toc, PARALLEL_KEY_WAL_USAGE, false);
@@ -2375,3 +2261,235 @@ _gin_compare_tuples(GinTuple *a, GinTuple *b, SortSupport ssup)
 	return ItemPointerCompare(GinTupleGetFirst(a),
 							  GinTupleGetFirst(b));
 }
+
+static double
+_gin_partition_sorted_data(GinBuildState *state)
+{
+	GinTuple   *tup;
+	Size		tuplen;
+	GinBuildShared *shared = state->bs_leader->ginshared;
+	BufFile   **files;
+	int64		fileidx = 0;
+	double		reltuples;
+
+	/* how many tuples per worker */
+	int64		worker_tuples = (state->indtuples / shared->scantuplesortstates) + 1;
+	int64		remaining = Min(worker_tuples, 1000);
+	int64		ntmp = 0;
+
+	/* wait for workers to scan table and produce partial results */
+	reltuples = _gin_parallel_heapscan(state);
+
+	/* do the actual sort in the leader */
+	tuplesort_performsort(state->bs_sortstate);
+
+	/* Allocate BufFiles, one for each participants. */
+	files = palloc0_array(BufFile *, shared->scantuplesortstates);
+
+	for (int i = 0; i < shared->scantuplesortstates; i++)
+	{
+		char		fname[MAXPGPATH];
+
+		sprintf(fname, "worker-%d", i);
+
+		files[i] = BufFileCreateFileSet(&shared->fileset.fs, fname);
+	}
+
+	/*
+	 * Read the GIN tuples from the shared tuplesort, sorted by category and
+	 * key. That probably gives us order matching how data is organized in the
+	 * index.
+	 *
+	 * We don't insert the GIN tuples right away, but instead accumulate as
+	 * many TIDs for the same key as possible, and then insert that at once.
+	 * This way we don't need to decompress/recompress the posting lists, etc.
+	 *
+	 * XXX Maybe we should sort by key first, then by category? The idea is
+	 * that if this matches the order of the keys in the index, we'd insert
+	 * the entries in order better matching the index.
+	 */
+	while ((tup = tuplesort_getgintuple(state->bs_sortstate, &tuplen, true)) != NULL)
+	{
+		ntmp++;
+
+		CHECK_FOR_INTERRUPTS();
+
+		/*
+		 * FIXME Maybe move to next partition only when the index key changes?
+		 * Otherwise we might have issues with 'could not fit onto page' when
+		 * adding overlapping TID lists to the index. But maybe it can't with
+		 * the merging of data in the tuplesort?
+		 */
+
+		BufFileWrite(files[fileidx], &tuplen, sizeof(tuplen));
+		BufFileWrite(files[fileidx], tup, tuplen);
+
+		remaining--;
+
+		/* move to the next file */
+		if (remaining == 0)
+		{
+			remaining = Min(worker_tuples, 1000);
+			fileidx++;
+			fileidx = fileidx % shared->scantuplesortstates;
+		}
+	}
+
+	/* close the files */
+	for (int i = 0; i < shared->scantuplesortstates; i++)
+	{
+		BufFileClose(files[i]);
+	}
+
+	/* and also close the tuplesort */
+	tuplesort_end(state->bs_sortstate);
+
+	/* wait for the leader to partition the data */
+	if (BarrierArriveAndWait(&shared->build_barrier,
+							 WAIT_EVENT_GIN_BUILD_PARTITION))
+		elog(LOG, "data partitioned, leader continues");
+
+	return reltuples;
+}
+
+static void
+_gin_parallel_insert(GinBuildState *state, GinBuildShared *ginshared,
+					 Relation heap, Relation index, bool progress)
+{
+	GinBuffer  *buffer;
+	GinTuple   *tup;
+	Size		len;
+
+	BufFile    *file;
+	char		fname[MAXPGPATH];
+	char	   *buff;
+	int64		ntuples = 0;
+	Size		maxlen;
+
+	/*
+	 * Initialize buffer to combine entries for the same key.
+	 *
+	 * The leader is allowed to use the whole maintenance_work_mem buffer to
+	 * combine data. The parallel workers already completed.
+	 */
+	buffer = GinBufferInit(state->ginstate.index);
+
+
+	sprintf(fname, "worker-%d", ParallelWorkerNumber + 1);
+	file = BufFileOpenFileSet(&ginshared->fileset.fs, fname, O_RDONLY, false);
+
+	/* 8kB seems like a reasonable starting point */
+	maxlen = 8192;
+	buff = palloc(maxlen);
+
+	while (true)
+	{
+		size_t		ret;
+
+		ret = BufFileRead(file, &len, sizeof(len));
+
+		if (ret == 0)
+			break;
+		if (ret != sizeof(len))
+			elog(ERROR, "incorrect data %zu %zu", ret, sizeof(len));
+
+		/* maybe resize the buffer */
+		if (maxlen < len)
+		{
+			while (maxlen < len)
+				maxlen *= 2;
+
+			buff = repalloc(buff, maxlen);
+		}
+
+		tup = (GinTuple *) buff;
+
+
+		BufFileReadExact(file, tup, len);
+
+		ntuples++;
+
+		if (ntuples % 100000 == 0)
+			elog(LOG, "inserted " INT64_FORMAT " tuples", ntuples);
+
+		CHECK_FOR_INTERRUPTS();
+
+		/*
+		 * If the buffer can accept the new GIN tuple, just store it there and
+		 * we're done. If it's a different key (or maybe too much data) flush
+		 * the current contents into the index first.
+		 */
+		if (!GinBufferCanAddKey(buffer, tup))
+		{
+			/*
+			 * Buffer is not empty and it's storing a different key - flush
+			 * the data into the insert, and start a new entry for current
+			 * GinTuple.
+			 */
+			AssertCheckItemPointers(buffer);
+			Assert(!PointerIsValid(buffer->cached));
+
+			ginEntryInsert(&state->ginstate,
+						   buffer->attnum, buffer->key, buffer->category,
+						   buffer->items, buffer->nitems, &state->buildStats);
+
+			/* discard the existing data */
+			GinBufferReset(buffer);
+		}
+
+		/*
+		 * We're about to add a GIN tuple to the buffer - check the memory
+		 * limit first, and maybe write out some of the data into the index
+		 * first, if needed (and possible). We only flush the part of the TID
+		 * list that we know won't change, and only if there's enough data for
+		 * compression to work well.
+		 */
+		if (GinBufferShouldTrim(buffer, tup))
+		{
+			Assert(buffer->nfrozen > 0);
+
+			/*
+			 * Buffer is not empty and it's storing a different key - flush
+			 * the data into the insert, and start a new entry for current
+			 * GinTuple.
+			 */
+			AssertCheckItemPointers(buffer);
+			Assert(!PointerIsValid(buffer->cached));
+
+			ginEntryInsert(&state->ginstate,
+						   buffer->attnum, buffer->key, buffer->category,
+						   buffer->items, buffer->nfrozen, &state->buildStats);
+
+			/* truncate the data we've just discarded */
+			GinBufferTrim(buffer);
+		}
+
+		/*
+		 * Remember data for the current tuple (either remember the new key,
+		 * or append if to the existing data).
+		 */
+		GinBufferMergeTuple(buffer, tup);
+
+		if (buffer->cached)
+			GinBufferUnpackCached(buffer, 0);
+	}
+
+	/* flush data remaining in the buffer (for the last key) */
+	if (!GinBufferIsEmpty(buffer))
+	{
+		AssertCheckItemPointers(buffer);
+
+		Assert(!PointerIsValid(buffer->cached));
+		ginEntryInsert(&state->ginstate,
+					   buffer->attnum, buffer->key, buffer->category,
+					   buffer->items, buffer->nitems, &state->buildStats);
+
+		/* discard the existing data */
+		GinBufferReset(buffer);
+	}
+
+	/* relase all the memory */
+	GinBufferFree(buffer);
+
+	BufFileClose(file);
+}
diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt
index e199f071628..afb9be848a0 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -116,6 +116,8 @@ CHECKPOINT_DELAY_START	"Waiting for a backend that blocks a checkpoint from star
 CHECKPOINT_DONE	"Waiting for a checkpoint to complete."
 CHECKPOINT_START	"Waiting for a checkpoint to start."
 EXECUTE_GATHER	"Waiting for activity from a child process while executing a <literal>Gather</literal> plan node."
+GIN_BUILD_SCAN	"Wait for scan of data during parallel GIN index build."
+GIN_BUILD_PARTITION	"Wait for partition of data during parallel GIN index build."
 HASH_BATCH_ALLOCATE	"Waiting for an elected Parallel Hash participant to allocate a hash table."
 HASH_BATCH_ELECT	"Waiting to elect a Parallel Hash participant to allocate a hash table."
 HASH_BATCH_LOAD	"Waiting for other Parallel Hash participants to finish loading a hash table."
-- 
2.48.1