From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> |
Cc: | pgsql-hackers(at)postgresql(dot)org, heikki(dot)linnakangas(at)enterprisedb(dot)com, masao(dot)fujii(at)gmail(dot)com |
Subject: | Re: Checkpointer on hot standby runs without looking checkpoint_segments |
Date: | 2012-06-08 09:02:53 |
Message-ID: | CA+U5nMK9zw69t6KVJzwYxq2HD_S4vMy6Y5xntFbh19ST-cX45A@mail.gmail.com |
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Lists: | pgsql-hackers |
On 8 June 2012 09:14, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> The requirement for this patch is as follows.
>
> - What I want to get is similarity of the behaviors between
> master and (hot-)standby concerning checkpoint
> progression. Specifically, checkpoints for streaming
> replication running at the speed governed with
> checkpoint_segments. The work of this patch is avoiding to get
> unexpectedly large number of WAL segments stay on standby
> side. (Plus, increasing the chance to skip recovery-end
> checkpoint by my another patch.)
Since we want wal_keep_segments number of WAL files on master (and
because of cascading, on standby also), I don't see any purpose to
triggering more frequent checkpoints just so we can hit a magic number
that is most often set wrong.
ISTM that we should avoid triggering a checkpoint on the master if
checkpoint_segments is less than wal_keep_segments. Such checkpoints
serve no purpose because we don't actually limit and recycle the WAL
files and all it does is slow people down.
Also, I don't believe that throwing more checkpoints makes it more
likely we can skip shutdown checkpoints at failover.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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