| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: ProcessStandbyHSFeedbackMessage can make global xmin go backwards |
| Date: | 2011-10-21 01:07:04 |
| Message-ID: | 1319156697-sup-3655@alvh.no-ip.org |
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| Thread: | |
| Lists: | pgsql-hackers |
Excerpts from Tom Lane's message of jue oct 20 19:20:19 -0300 2011:
> So I've concluded that there's just no point in the GetOldestXmin
> clamping, and we should just apply the xmin value we get from the
> standby if it passes basic sanity checks (the epoch test), and hope that
> we're not too late to prevent loss of the data the standby wanted.
I am happy that the HS patch has introduced uses for the xid epoch. I
had to use them for multixact truncation in the FK locks patch, and was
nervous because I wasn't seeing any user in core code other than the
txid functions; this lack of callers, added to the comments in
GetNextXidAndEpoch ("we do not support such things"), made me feel a bit
uncomfortable about using it. I'm happy to have this problem out of my
mind now.
--
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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