From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Theo Schlossnagle <jesus(at)omniti(dot)com> |
Cc: | Andrew Dunstan <andrew(at)dunslane(dot)net>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, pgsql-patches(at)postgresql(dot)org |
Subject: | Re: Expose checkpoint start/finish times into SQL. |
Date: | 2008-04-04 01:58:46 |
Message-ID: | 416.1207274326@sss.pgh.pa.us |
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Lists: | pgsql-patches |
Theo Schlossnagle <jesus(at)omniti(dot)com> writes:
> Heikki: It it useful for knowing when the last checkpoint occurred.
I guess I'm wondering why that's important. In the current bgwriter
design, the system spends half its time checkpointing (or in general
checkpoint_completion_target % of the time). So this seems fairly close
to wanting to know when the bgwriter last wrote a dirty buffer --- yeah,
I can imagine scenarios for wanting to know that, but they probably
require a whole pile of other knowledge as well.
JD seems to have gone off into the weeds imagining that this patch would
provide tracking of the last N checkpoints; which might start to
approach the level of an interesting feature, except that it's still not
clear *why* those numbers are interesting, given the bgwriter's
propensity to try to hold the checkpoint duration constant.
regards, tom lane
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