Speedup truncations of relation forks.

When a relation is truncated, shared_buffers needs to be scanned
so that any buffers for the relation forks are invalidated in it.
Previously, shared_buffers was scanned for each relation forks, i.e.,
MAIN, FSM and VM, when VACUUM truncated off any empty pages
at the end of relation or TRUNCATE truncated the relation in place.
Since shared_buffers needed to be scanned multiple times,
it could take a long time to finish those commands especially
when shared_buffers was large.

This commit changes the logic so that shared_buffers is scanned only
one time for those three relation forks.

Author: Kirk Jamison
Reviewed-by: Masahiko Sawada, Thomas Munro, Alvaro Herrera, Takayuki Tsunakawa and Fujii Masao
Discussion: https://postgr.es/m/D09B13F772D2274BB348A310EE3027C64E2067@g01jpexmbkw24

1 files changed, 21 insertions, 9 deletions

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 6f3a4028547..483f705305c 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -2901,7 +2901,7 @@ BufferGetLSNAtomic(Buffer buffer)
  *		DropRelFileNodeBuffers
  *
  *		This function removes from the buffer pool all the pages of the
- *		specified relation fork that have block numbers >= firstDelBlock.
+ *		specified relation forks that have block numbers >= firstDelBlock.
  *		(In particular, with firstDelBlock = 0, all pages are removed.)
  *		Dirty pages are simply dropped, without bothering to write them
  *		out first.  Therefore, this is NOT rollback-able, and so should be
@@ -2924,16 +2924,21 @@ BufferGetLSNAtomic(Buffer buffer)
  * --------------------------------------------------------------------
  */
 void
-DropRelFileNodeBuffers(RelFileNodeBackend rnode, ForkNumber forkNum,
-					   BlockNumber firstDelBlock)
+DropRelFileNodeBuffers(RelFileNodeBackend rnode, ForkNumber *forkNum,
+					   int nforks, BlockNumber *firstDelBlock)
 {
 	int			i;
+	int			j;
 
 	/* If it's a local relation, it's localbuf.c's problem. */
 	if (RelFileNodeBackendIsTemp(rnode))
 	{
 		if (rnode.backend == MyBackendId)
-			DropRelFileNodeLocalBuffers(rnode.node, forkNum, firstDelBlock);
+		{
+			for (j = 0; j < nforks; j++)
+				DropRelFileNodeLocalBuffers(rnode.node, forkNum[j],
+											firstDelBlock[j]);
+		}
 		return;
 	}
 
@@ -2962,11 +2967,18 @@ DropRelFileNodeBuffers(RelFileNodeBackend rnode, ForkNumber forkNum,
 			continue;
 
 		buf_state = LockBufHdr(bufHdr);
-		if (RelFileNodeEquals(bufHdr->tag.rnode, rnode.node) &&
-			bufHdr->tag.forkNum == forkNum &&
-			bufHdr->tag.blockNum >= firstDelBlock)
-			InvalidateBuffer(bufHdr);	/* releases spinlock */
-		else
+
+		for (j = 0; j < nforks; j++)
+		{
+			if (RelFileNodeEquals(bufHdr->tag.rnode, rnode.node) &&
+				bufHdr->tag.forkNum == forkNum[j] &&
+				bufHdr->tag.blockNum >= firstDelBlock[j])
+			{
+				InvalidateBuffer(bufHdr); /* releases spinlock */
+				break;
+			}
+		}
+		if (j >= nforks)
 			UnlockBufHdr(bufHdr, buf_state);
 	}
 }