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commit    c3e775e608f2a6d0bcfba147bf08a506827cc567
Author:   Melanie Plageman <melanieplageman@gmail.com>
Date:     Fri Feb 14 17:57:03 2025 +0000
First released in: 18.0

    Use streaming read I/O in VACUUM's third phase
    
    Make vacuum's third phase (its second pass over the heap), which reaps
    dead items collected in the first phase and marks them as reusable, use
    the read stream API. This commit adds a new read stream callback,
    vacuum_reap_lp_read_stream_next(), that looks ahead in the TidStore and
    returns the next block number to read for vacuum.
    
    Author: Melanie Plageman <melanieplageman@gmail.com>
    Co-authored-by: Thomas Munro <thomas.munro@gmail.com>
    Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
    Discussion: https://postgr.es/m/CA%2BhUKGKN3oy0bN_3yv8hd78a4%2BM1tJC9z7mD8%2Bf%2ByA%2BGeoFUwQ%40mail.gmail.com


 src/backend/access/heap/vacuumlazy.c | 55 ++++++++++++++++++++++++++++++++----
 1 file changed, 49 insertions(+), 6 deletions(-)

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 08d89ab2bcd..74175e00534 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -2640,6 +2640,32 @@ lazy_vacuum_all_indexes(LVRelState *vacrel)
 	return allindexes;
 }
 
+/*
+ * Read stream callback for vacuum's third phase (second pass over the heap).
+ * Gets the next block from the TID store and returns it or InvalidBlockNumber
+ * if there are no further blocks to vacuum.
+ */
+static BlockNumber
+vacuum_reap_lp_read_stream_next(ReadStream *stream,
+								void *callback_private_data,
+								void *per_buffer_data)
+{
+	TidStoreIter *iter = callback_private_data;
+	TidStoreIterResult *iter_result;
+
+	iter_result = TidStoreIterateNext(iter);
+	if (iter_result == NULL)
+		return InvalidBlockNumber;
+
+	/*
+	 * Save the TidStoreIterResult for later, so we can extract the offsets.
+	 * It is safe to copy the result, according to TidStoreIterateNext().
+	 */
+	memcpy(per_buffer_data, iter_result, sizeof(*iter_result));
+
+	return iter_result->blkno;
+}
+
 /*
  *	lazy_vacuum_heap_rel() -- second pass over the heap for two pass strategy
  *
@@ -2660,11 +2686,11 @@ lazy_vacuum_all_indexes(LVRelState *vacrel)
 static void
 lazy_vacuum_heap_rel(LVRelState *vacrel)
 {
+	ReadStream *stream;
 	BlockNumber vacuumed_pages = 0;
 	Buffer		vmbuffer = InvalidBuffer;
 	LVSavedErrInfo saved_err_info;
 	TidStoreIter *iter;
-	TidStoreIterResult *iter_result;
 
 	Assert(vacrel->do_index_vacuuming);
 	Assert(vacrel->do_index_cleanup);
@@ -2680,20 +2706,37 @@ lazy_vacuum_heap_rel(LVRelState *vacrel)
 							 InvalidBlockNumber, InvalidOffsetNumber);
 
 	iter = TidStoreBeginIterate(vacrel->dead_items);
-	while ((iter_result = TidStoreIterateNext(iter)) != NULL)
+
+	/* Set up the read stream for vacuum's second pass through the heap */
+	stream = read_stream_begin_relation(READ_STREAM_MAINTENANCE,
+										vacrel->bstrategy,
+										vacrel->rel,
+										MAIN_FORKNUM,
+										vacuum_reap_lp_read_stream_next,
+										iter,
+										sizeof(TidStoreIterResult));
+
+	while (true)
 	{
 		BlockNumber blkno;
 		Buffer		buf;
 		Page		page;
+		TidStoreIterResult *iter_result;
 		Size		freespace;
 		OffsetNumber offsets[MaxOffsetNumber];
 		int			num_offsets;
 
 		vacuum_delay_point(false);
 
-		blkno = iter_result->blkno;
-		vacrel->blkno = blkno;
+		buf = read_stream_next_buffer(stream, (void **) &iter_result);
 
+		/* The relation is exhausted */
+		if (!BufferIsValid(buf))
+			break;
+
+		vacrel->blkno = blkno = BufferGetBlockNumber(buf);
+
+		Assert(iter_result);
 		num_offsets = TidStoreGetBlockOffsets(iter_result, offsets, lengthof(offsets));
 		Assert(num_offsets <= lengthof(offsets));
 
@@ -2705,8 +2748,6 @@ lazy_vacuum_heap_rel(LVRelState *vacrel)
 		visibilitymap_pin(vacrel->rel, blkno, &vmbuffer);
 
 		/* We need a non-cleanup exclusive lock to mark dead_items unused */
-		buf = ReadBufferExtended(vacrel->rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
-								 vacrel->bstrategy);
 		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
 		lazy_vacuum_heap_page(vacrel, blkno, buf, offsets,
 							  num_offsets, vmbuffer);
@@ -2719,6 +2760,8 @@ lazy_vacuum_heap_rel(LVRelState *vacrel)
 		RecordPageWithFreeSpace(vacrel->rel, blkno, freespace);
 		vacuumed_pages++;
 	}
+
+	read_stream_end(stream);
 	TidStoreEndIterate(iter);
 
 	vacrel->blkno = InvalidBlockNumber;


[parent: 9256822608f3]