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Re: Re: Hot Standby query cancellation and Streaming Replication integration

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
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 (view raw or flat)
Thread:
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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