From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
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To: | Greg Stark <gsstark(at)mit(dot)edu> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Re: Hot Standby query cancellation and Streaming Replication integration |
Date: | 2010-02-27 06:53:24 |
Message-ID: | 4B88C164.6070205@enterprisedb.com |
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Lists: | pgsql-hackers |
Greg Stark wrote:
> On Fri, Feb 26, 2010 at 9:19 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> There's *definitely* not going to be enough information in the WAL
>> stream coming from a master that doesn't think it has HS slaves.
>> We can't afford to record all that extra stuff in installations for
>> which it's just useless overhead. BTW, has anyone made any attempt
>> to measure the performance hit that the patch in its current form is
>> creating via added WAL entries?
>
> What extra entries?
* An xact-assignment record is written every PGPROC_MAX_CACHED_SUBXIDS
(= 64) subtransaction ids assigned to a single top-level transaction.
* A running-xacts record is written at every online checkpoint
* A btree-reuse-page record is written whenever a dead b-tree page is
recycled
* A vacuum cleanup-info record is written once per VACUUM of a table
* A standby-lock record is written for each AccessExclusiveLock acquired.
Am I missing something?
I doubt any of these are noticeable, though I don't think anyone has
measured it.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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