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| author | Heikki Linnakangas <heikki.linnakangas@iki.fi> | 2016-09-29 13:16:30 +0300 |
|---|---|---|
| committer | Heikki Linnakangas <heikki.linnakangas@iki.fi> | 2016-09-29 13:16:30 +0300 |
| commit | 6e654546fb61f62cc982d0c8f62241b3b30e7ef8 (patch) | |
| tree | 8c94b730bf7e132b05bfe0411227bc25cf0cd062 | |
| parent | 6ad8ac6026287e3ccbc4d606b6ab6116ccc0eec8 (diff) | |
| download | postgresql-6e654546fb61f62cc982d0c8f62241b3b30e7ef8.tar.gz postgresql-6e654546fb61f62cc982d0c8f62241b3b30e7ef8.zip | |
Don't bother to lock bufmgr partitions in pg_buffercache.
That makes the view a lot less disruptive to use on a production system.
Without the locks, you don't get a consistent snapshot across all buffers,
but that's OK. It wasn't a very useful guarantee in practice.
Ivan Kartyshov, reviewed by Tomas Vondra and Robert Haas.
Discusssion: <f9d6cab2-73a7-7a84-55a8-07dcb8516ae5@postgrespro.ru>
| -rw-r--r-- | contrib/pg_buffercache/pg_buffercache_pages.c | 23 |
1 files changed, 4 insertions, 19 deletions
diff --git a/contrib/pg_buffercache/pg_buffercache_pages.c b/contrib/pg_buffercache/pg_buffercache_pages.c index da13bde3595..8bebf2384df 100644 --- a/contrib/pg_buffercache/pg_buffercache_pages.c +++ b/contrib/pg_buffercache/pg_buffercache_pages.c @@ -136,17 +136,12 @@ pg_buffercache_pages(PG_FUNCTION_ARGS) MemoryContextSwitchTo(oldcontext); /* - * To get a consistent picture of the buffer state, we must lock all - * partitions of the buffer map. Needless to say, this is horrible - * for concurrency. Must grab locks in increasing order to avoid - * possible deadlocks. - */ - for (i = 0; i < NUM_BUFFER_PARTITIONS; i++) - LWLockAcquire(BufMappingPartitionLockByIndex(i), LW_SHARED); - - /* * Scan through all the buffers, saving the relevant fields in the * fctx->record structure. + * + * We don't hold the partition locks, so we don't get a consistent + * snapshot across all buffers, but we do grab the buffer header + * locks, so the information of each buffer is self-consistent. */ for (i = 0; i < NBuffers; i++) { @@ -179,16 +174,6 @@ pg_buffercache_pages(PG_FUNCTION_ARGS) UnlockBufHdr(bufHdr, buf_state); } - - /* - * And release locks. We do this in reverse order for two reasons: - * (1) Anyone else who needs more than one of the locks will be trying - * to lock them in increasing order; we don't want to release the - * other process until it can get all the locks it needs. (2) This - * avoids O(N^2) behavior inside LWLockRelease. - */ - for (i = NUM_BUFFER_PARTITIONS; --i >= 0;) - LWLockRelease(BufMappingPartitionLockByIndex(i)); } funcctx = SRF_PERCALL_SETUP(); |