Re: Checkpointer on hot standby runs without looking checkpoint_segments

On Fri, Jun 8, 2012 at 9:58 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On 8 June 2012 14:47, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
>>> 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.
>>
>> On the other hand, I emphatically disagree with this, for the same
>> reasons as on the other thread.  Getting data down to disk provides a
>> greater measure of safety than having it in memory.  Making
>> checkpoint_segments not force a checkpoint is no better than making
>> checkpoint_timeout not force a checkpoint.
>
> Not sure which bit you are disagreeing with. I have no suggested
> change to checkpoint_timeout.

You already made it not a hard timeout. We have another nearby thread
discussing why I don't like that.

> What I'm saying is that forcing a checkpoint to save space, when we
> aren't going to save space, makes no sense.

We are also forcing a checkpoint to limit recovery time and data loss
potential, not just to save space.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company