From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <stark(at)mit(dot)edu>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Autoanalyze and OldestXmin |
Date: | 2011-06-09 14:36:59 |
Message-ID: | BANLkTim4Mod9UFDTDwDKPqbGCMHFJ22ZTQ@mail.gmail.com |
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Lists: | pgsql-hackers |
On Thu, Jun 9, 2011 at 2:20 AM, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> wrote:
> Ah, I see. Would there will be benefits if we can do some special handling
> for cases where we know that ANALYZE is running outside a transaction block
> and that its not going to invoke any user-defined functions ?
We'd have to distinguish between user-defined typanalyze functions and
system-defined typanalyze functions, which doesn't seem to appealing,
or robust.
> If user is
> running ANALYZE inside a transaction block, he is probably already aware and
> ready to handle long-running transaction. But running them under the covers
> as part of auto-analyze does not see quite right. The pgbench test already
> shows the severe bloat that a long running analyze may cause for small
> tables and many wasteful vacuum runs on those tables.
> Another idea would be to split the ANALYZE into multiple small transactions,
> each taking a new snapshot. That might result in bad statistics if the table
> is undergoing huge change, but in that case, the stats will be outdated soon
> anyways if we run with a old snapshot. I understand there could be issues
> like counting the same tuple twice or more, but would that be a common case
> to worry about ?
I am wondering if we shouldn't be asking ourselves a different
question: why is ANALYZE running long enough on your tables for this
to become an issue? How long is it taking?
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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