| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-performance(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: freezing tuples ( was: Why is vacuum_freeze_min_age 100m? ) |
| Date: | 2009-08-13 21:58:04 |
| Message-ID: | 20090813215804.GV5909@alvh.no-ip.org |
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| Thread: | |
| Lists: | pgsql-hackers pgsql-performance |
Jeff Davis wrote:
> Why aren't we more opportunistic about freezing tuples? For instance, if
> we already have a dirty buffer in cache, we should be more aggressive
> about freezing those tuples than freezing tuples on disk.
The most widely cited reason is that you lose forensics data. Although
they are increasingly rare, there are still situations in which the heap
tuple machinery messes up and the xmin/xmax/etc fields of the tuple are
the best/only way to find out what happened and thus fix the bug. If
you freeze early, there's just no way to know.
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
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