| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Optimizing Read-Only Scalability |
| Date: | 2009-05-14 17:55:27 |
| Message-ID: | 16261.1242323727@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Thu, May 14, 2009 at 1:28 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> GetSnapshotData doesn't take an exclusive lock. Neither does start or
>> end of a read-only transaction. AFAIK there is no reason, and certainly
>> no shred of experimental evidence, to think that ProcArrayLock
>> contention is the bottleneck for read-only scenarios.
> I think Simon's point was that it is O(n) rather than O(1), not that
> it took an exclusive lock.
I think my point was that there's no evidence that GetSnapshotData
is where the scalability issue is. Without some evidence there's no
point in kluging it up.
regards, tom lane
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