| From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
|---|---|
| To: | Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au> |
| Cc: | Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl>, Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Multiple Xids in PGPROC? |
| Date: | 2004-05-05 04:02:14 |
| Message-ID: | 200405050402.i4542Er23789@candle.pha.pa.us |
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| Lists: | pgsql-hackers |
Christopher Kings-Lynne wrote:
> > I remember going through this. Other backends will use pg_subtrans to
> > know what transactions are in progress. They have to do the standard
> > lookups to find the status of the parent transaction. The backend-local
> > list of xids is needed so the commit can clean up those subtransaction
> > xids so that later transactions don't have to use pg_subtrans.
>
> Is there some solution whereby the common case (99.999% of transactions
> won't be subtransactoins) is fast, and the uncommon case of being in a
> subtransaction is slower?
Yes, we use an unreserved clog status to indicate a pg_subtrans lookup
is required. In non-subtrans cases, no pg_subtrans lookup is required.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
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