mirror/postgresql
2
0
Fork 0
mirror of https://git.postgresql.org/git/postgresql.git synced 2025-01-06 15:24:56 +08:00
Code Issues Packages Projects Releases Wiki Activity

Add a comment documenting the question of whether PrefetchBuffer should

Browse Source 
try to protect an already-existing buffer from being evicted.  This was
left as an open issue when the posix_fadvise patch was committed.  I'm
not sure there's any evidence to justify more work in this area, but we
should have some record about it in the source code.
This commit is contained in:
Tom Lane 2009-04-03 18:17:43 +00:00
parent cd331e4b84
commit 1b2bb33a54
1 changed files with 13 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
src/backend/storage/buffer/bufmgr.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.250 2009/03/31 22:12:48 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.251 2009/04/03 18:17:43 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -153,6 +153,18 @@ PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum)
/* If not in buffers, initiate prefetch */
if (buf_id < 0)
smgrprefetch(reln->rd_smgr, forkNum, blockNum);
/*
* If the block *is* in buffers, we do nothing. This is not really
* ideal: the block might be just about to be evicted, which would
* be stupid since we know we are going to need it soon. But the
* only easy answer is to bump the usage_count, which does not seem
* like a great solution: when the caller does ultimately touch the
* block, usage_count would get bumped again, resulting in too much
* favoritism for blocks that are involved in a prefetch sequence.
* A real fix would involve some additional per-buffer state, and
* it's not clear that there's enough of a problem to justify that.
*/
}
#endif /* USE_PREFETCH */
}