| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
| Cc: | ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org, Katsuhiko Okano <okano(dot)katsuhiko(at)oss(dot)ntt(dot)co(dot)jp> |
| Subject: | Re: CSStorm occurred again by postgreSQL8.2 |
| Date: | 2006-08-07 19:42:31 |
| Message-ID: | 13175.1154979751@sss.pgh.pa.us |
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| Lists: | pgsql-hackers pgsql-patches |
Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Tom Lane wrote:
>> I'm wondering about doing something similar to what
>> TransactionIdIsInProgress does, ie, make use of the PGPROC lists
>> of live subtransactions.
> Well, that sounds awfully more expensive than setting
> local-to-my-database Xmins as well as global (all databases) Xmins :-)
Only when you've got a lot of subtransactions. The point of this
discussion is to optimize for the few-or-none case. In any case,
the problem with the local/global bit was that you'd be expending
foreground-process cycles without any foreground-process return.
Being able to use a snapshot without consulting pg_subtrans will
certainly buy back some cycles...
regards, tom lane
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