Re: Hot standby having high requested checkpoints?

I just now ran the following query a few times after each other on the
hot standby:

select now(), * from pg_stat_bgwriter;

Here are the results:

now | checkpoints_timed | checkpoints_req |
buffers_checkpoint | buffers_clean | maxwritten_clean | buffers_backend
| buffers_alloc
-------------------------------+-------------------+-----------------+--------------------+---------------+------------------+-----------------+---------------
2012-03-01 23:24:49.099194+00 | 11546 | 145300
| 1000409459 | 38483026 | 170724 |
5058186 | 438703950
2012-03-01 23:24:52.139176+00 | 11546 | 145300
| 1000409459 | 38483027 | 170724 |
5058191 | 438703975
2012-03-01 23:24:59.129171+00 | 11546 | 145302
| 1000409459 | 38483081 | 170724 |
5058214 | 438704438
2012-03-01 23:25:05.957532+00 | 11546 | 145304
| 1000409459 | 38483118 | 170724 |
5058230 | 438704689
2012-03-01 23:25:09.519175+00 | 11546 | 145305
| 1000409459 | 38483160 | 170724 |
5058239 | 438704968
2012-03-01 23:25:37.019194+00 | 11546 | 145308
| 1000409459 | 38483259 | 170724 |
5058255 | 438705566
2012-03-01 23:25:40.659164+00 | 11546 | 145308
| 1000409459 | 38483268 | 170724 |
5058257 | 438705639
2012-03-01 23:25:47.239281+00 | 11546 | 145309
| 1000409459 | 38483283 | 170724 |
5058266 | 438705815
2012-03-01 23:26:23.858716+00 | 11546 | 145312
| 1000409459 | 38483393 | 170724 |
5058307 | 438706561
2012-03-01 23:26:46.467493+00 | 11546 | 145317
| 1000409670 | 38483524 | 170724 |
5058354 | 438707619

in two minutes, I saw 17 checkpoints_req, and the number of
buffers_checkpoint didn't budge till the last few and even then not much.

checkpoint_segments = 256

- Brian F

On 03/01/2012 01:35 AM, Simon Riggs wrote:
> On Tue, Feb 28, 2012 at 10:53 PM, Brian Fehrle
> <brianf(at)consistentstate(dot)com> wrote:
>
>> I have two PostgreSQL 9.0.5 clusters, one is a master and the other is a hot
>> standby via streaming replication. I'm monitoring some stats on each and I'm
>> noticing something very odd. On the master, I get between 2 and 4 requested
>> checkpoints per hour, but on the hot standby I'm seeing between 200 and 300
>> requested checkpoints per hour.
> We don't do a restartpoint on the standby unless we see a checkpoint
> record, so that result should be impossible.
>
> So I'm guessing you're reading the stats wrong?
>