Cache smgrnblocks() results in recovery.

Avoid repeatedly calling lseek(SEEK_END) during recovery by caching
the size of each fork.  For now, we can't use the same technique in
other processes, because we lack a shared invalidation mechanism.

Do this by generalizing the pre-existing caching used by FSM and VM
to support all forks.

Discussion: https://postgr.es/m/CAEepm%3D3SSw-Ty1DFcK%3D1rU-K6GSzYzfdD4d%2BZwapdN7dTa6%3DnQ%40mail.gmail.com

1 files changed, 14 insertions, 13 deletions

diff --git a/src/backend/storage/freespace/freespace.c b/src/backend/storage/freespace/freespace.c
index 95a21f6cc38..6a96126b0c2 100644
--- a/src/backend/storage/freespace/freespace.c
+++ b/src/backend/storage/freespace/freespace.c
@@ -541,18 +541,19 @@ fsm_readbuf(Relation rel, FSMAddress addr, bool extend)
 	 * value might be stale.  (We send smgr inval messages on truncation, but
 	 * not on extension.)
 	 */
-	if (rel->rd_smgr->smgr_fsm_nblocks == InvalidBlockNumber ||
-		blkno >= rel->rd_smgr->smgr_fsm_nblocks)
+	if (rel->rd_smgr->smgr_cached_nblocks[FSM_FORKNUM] == InvalidBlockNumber ||
+		blkno >= rel->rd_smgr->smgr_cached_nblocks[FSM_FORKNUM])
 	{
+		/* Invalidate the cache so smgrnblocks asks the kernel. */
+		rel->rd_smgr->smgr_cached_nblocks[FSM_FORKNUM] = InvalidBlockNumber;
 		if (smgrexists(rel->rd_smgr, FSM_FORKNUM))
-			rel->rd_smgr->smgr_fsm_nblocks = smgrnblocks(rel->rd_smgr,
-														 FSM_FORKNUM);
+			smgrnblocks(rel->rd_smgr, FSM_FORKNUM);
 		else
-			rel->rd_smgr->smgr_fsm_nblocks = 0;
+			rel->rd_smgr->smgr_cached_nblocks[FSM_FORKNUM] = 0;
 	}
 
 	/* Handle requests beyond EOF */
-	if (blkno >= rel->rd_smgr->smgr_fsm_nblocks)
+	if (blkno >= rel->rd_smgr->smgr_cached_nblocks[FSM_FORKNUM])
 	{
 		if (extend)
 			fsm_extend(rel, blkno + 1);
@@ -621,14 +622,17 @@ fsm_extend(Relation rel, BlockNumber fsm_nblocks)
 	RelationOpenSmgr(rel);
 
 	/*
-	 * Create the FSM file first if it doesn't exist.  If smgr_fsm_nblocks is
-	 * positive then it must exist, no need for an smgrexists call.
+	 * Create the FSM file first if it doesn't exist.  If
+	 * smgr_cached_nblocks[FSM_FORKNUM] is positive then it must exist, no
+	 * need for an smgrexists call.
 	 */
-	if ((rel->rd_smgr->smgr_fsm_nblocks == 0 ||
-		 rel->rd_smgr->smgr_fsm_nblocks == InvalidBlockNumber) &&
+	if ((rel->rd_smgr->smgr_cached_nblocks[FSM_FORKNUM] == 0 ||
+		 rel->rd_smgr->smgr_cached_nblocks[FSM_FORKNUM] == InvalidBlockNumber) &&
 		!smgrexists(rel->rd_smgr, FSM_FORKNUM))
 		smgrcreate(rel->rd_smgr, FSM_FORKNUM, false);
 
+	/* Invalidate cache so that smgrnblocks() asks the kernel. */
+	rel->rd_smgr->smgr_cached_nblocks[FSM_FORKNUM] = InvalidBlockNumber;
 	fsm_nblocks_now = smgrnblocks(rel->rd_smgr, FSM_FORKNUM);
 
 	while (fsm_nblocks_now < fsm_nblocks)
@@ -640,9 +644,6 @@ fsm_extend(Relation rel, BlockNumber fsm_nblocks)
 		fsm_nblocks_now++;
 	}
 
-	/* Update local cache with the up-to-date size */
-	rel->rd_smgr->smgr_fsm_nblocks = fsm_nblocks_now;
-
 	UnlockRelationForExtension(rel, ExclusiveLock);
 }