Re: Unexpected trouble from pg_basebackup - Mailing list pgsql-general
| From | Magnus Hagander |
|---|---|
| Subject | Re: Unexpected trouble from pg_basebackup |
| Date | |
| Msg-id | CABUevExY9SDDD_d=o2DxECVA3zihmHjGEcAOrb=3=m4AgERDtw@mail.gmail.com Whole thread Raw |
| In response to | Unexpected trouble from pg_basebackup (otheus uibk <otheus.uibk@gmail.com>) |
| List | pgsql-general |
On Wed, Oct 5, 2016 at 3:55 PM, otheus uibk <otheus.uibk@gmail.com> wrote:
pg_basebackup will always send in a checkpoint. PostgreSQL will time that to take approximately checkpoint_timeout * checkpoint_completion_target time. So with checkpoint_timeout set to a very high value, it will by default target something like 30 minutes before it even gets started. The only reason it takes as *little* as it does is that your system is lightly loaded.
-- On Tue, Oct 4, 2016 at 10:49 PM, Magnus Hagander <magnus@hagander.net> wrote:On Tue, Oct 4, 2016 at 10:42 PM, otheus uibk <otheus.uibk@gmail.com> wrote:After a 3 to 4 minute delay, pg_basebackup started doing it's thing and finished within a few minutes. So now the question is: why the startup delay?
Sounds to me like it's doing a CHECKPOINT with spreading, which make it take time. Try with "-c fast" and see if the problem goes away.Maybe not too far off.2016-10-04 17:43:40.620 GMT 57eb90a0.6e07 402 00000 LOG: checkpoint complete: wrote 12799 buffers (1.0%); 0 transaction log file(s) added, 0 removed, 5 recycled; write=1389.348 s, sync=0.033 s, total=1389.400 s; sync files=240, longest=0.003 s, average=0.000 s; distance=92915 kB, estimate=129373 kB2016-10-04 18:20:31.714 GMT 57eb90a0.6e07 403 00000 LOG: checkpoint starting: time2016-10-04 18:39:19.870 GMT 57eb90a0.6e07 404 00000 LOG: checkpoint complete: wrote 10265 buffers (0.8%); 0 transaction log file(s) added, 0 removed, 4 recycled; write=1128.118 s, sync=0.023 s, total=1128.155 s; sync files=190, longest=0.002 s, average=0.000 s; distance=73419 kB, estimate=123778 kB2016-10-04 19:07:12.647 GMT [unknown] pgsync 57f3fde0.52e3 2 00000 LOG: replication connection authorized: user=pgsync2016-10-04 19:07:12.703 GMT 57eb90a0.6e07 405 00000 LOG: checkpoint starting: force wait2016-10-04 19:20:32.879 GMT [unknown] pgsync 57f40100.5891 2 00000 LOG: replication connection authorized: user=pgsync2016-10-04 19:23:05.249 GMT 57eb90a0.6e07 406 00000 LOG: checkpoint complete: wrote 8638 buffers (0.7%); 0 transaction log file(s) added, 0 removed, 5 recycled; write=952.514 s, sync=0.016 s, total=952.546 s; sync files=238, longest=0.002 s, average=0.000 s; distance=68257 kB, estimate=118226 kB2016-10-04 19:23:05.249 GMT 57eb90a0.6e07 407 00000 LOG: checkpoint starting: force wait2016-10-04 19:28:52.232 GMT 57eb90a0.6e07 408 00000 LOG: checkpoint complete: wrote 3102 buffers (0.2%); 0 transaction log file(s) added, 0 removed, 0 recycled; write=346.957 s, sync=0.018 s, total=346.982 s; sync files=149, longest=0.002 s, average=0.000 s; distance=36016 kB, estimate=110005 kB2016-10-04 19:30:31.922 GMT [unknown] pgsync 57f40357.5c70 2 00000 LOG: replication connection authorized: user=pgsync2016-10-04 19:30:31.932 GMT 57eb90a0.6e07 409 00000 LOG: checkpoint starting: force wait2016-10-04 19:33:40.857 GMT 57eb90a0.6e07 410 00000 LOG: checkpoint complete: wrote 1763 buffers (0.1%); 0 transaction log file(s) added, 0 removed, 1 recycled; write=188.886 s, sync=0.030 s, total=188.924 s; sync files=125, longest=0.004 s, average=0.000 s; distance=13135 kB, estimate=100318 kBOK, so what was happening is that the checkpoints were taking 5 to 15 minutes minutes, and aborted basebackups were triggering new checkpoints which waited on the previous ones.Is it possible the new environment is not high-performance enough??possibly relevant configuration change:checkpoint_timeout=1h
pg_basebackup will always send in a checkpoint. PostgreSQL will time that to take approximately checkpoint_timeout * checkpoint_completion_target time. So with checkpoint_timeout set to a very high value, it will by default target something like 30 minutes before it even gets started. The only reason it takes as *little* as it does is that your system is lightly loaded.
You can do a fast checkpoint with the parameter I suggested before, or you can tune your checkpoint_timeout to be something that gives you a more reasonable time.
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