On 8 June 2012 09:14, Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.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/
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