From: Andres Freund <andres@anarazel.de>
Date: Mon, 21 May 2018 22:43:30 +0000 (-0700)
Subject: freespace: Don't constantly close files when reading buffer.
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=96435b05c9546b6da829043fb10b2a7309216bd2;p=users%2Fandresfreund%2Fpostgres.git

freespace: Don't constantly close files when reading buffer.

fsm_readbuf() used to always do an smgrexists() when reading a buffer
beyond the known file size. That currently implies closing the md.c
handle, loosing all the data cached therein.  Change this to only
check for file existance when not already known to be larger than 0
blocks.

Author: Andres Freund
Reviewed-By:
Discussion: https://postgr.es/m/
Backpatch:
---

diff --git a/src/backend/storage/freespace/freespace.c b/src/backend/storage/freespace/freespace.c
index 65c4e74999..d7569cec5e 100644
--- a/src/backend/storage/freespace/freespace.c
+++ b/src/backend/storage/freespace/freespace.c
@@ -556,7 +556,7 @@ fsm_readbuf(Relation rel, FSMAddress addr, bool extend)
 	 * not on extension.)
 	 */
 	if (rel->rd_smgr->smgr_fsm_nblocks == InvalidBlockNumber ||
-		blkno >= rel->rd_smgr->smgr_fsm_nblocks)
+		rel->rd_smgr->smgr_fsm_nblocks == 0)
 	{
 		if (smgrexists(rel->rd_smgr, FSM_FORKNUM))
 			rel->rd_smgr->smgr_fsm_nblocks = smgrnblocks(rel->rd_smgr,
@@ -564,6 +564,9 @@ fsm_readbuf(Relation rel, FSMAddress addr, bool extend)
 		else
 			rel->rd_smgr->smgr_fsm_nblocks = 0;
 	}
+	else if (blkno >= rel->rd_smgr->smgr_fsm_nblocks)
+		rel->rd_smgr->smgr_fsm_nblocks = smgrnblocks(rel->rd_smgr,
+													 FSM_FORKNUM);
 
 	/* Handle requests beyond EOF */
 	if (blkno >= rel->rd_smgr->smgr_fsm_nblocks)