| From: | Dan Ports <drkp(at)csail(dot)mit(dot)edu> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Hakan Kocaman <hkocam(at)googlemail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: MIT benchmarks pgsql multicore (up to 48)performance |
| Date: | 2010-10-04 18:35:42 |
| Message-ID: | 20101004183542.GB2690@csail.mit.edu |
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| Thread: | |
| Lists: | pgsql-hackers pgsql-performance |
On Mon, Oct 04, 2010 at 01:13:36PM -0400, Robert Haas wrote:
> I believe the "one of only 16 global mutexes" comment is referring to
> NUM_LOCK_PARTITIONS (there's also NUM_BUFFER_PARTITIONS, but that
> wouldn't be relevant for row and table-level locks).
Yes -- my understanding is that they hit two lock-related problems:
1) LWLock contention caused by acquiring the same lock in compatible
modes (e.g. multiple shared locks)
2) false contention caused by acquiring two locks that hashed to the
same partition
and the first was the worse problem. The lock-free structures helpe
with both, so the impact of changing NUM_LOCK_PARTITIONS was less
interesting.
Dan
--
Dan R. K. Ports MIT CSAIL http://drkp.net/
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