Обсуждение: pg_basebackup and checkpoints
I tried (and finally succeeded) to do a base backup tonight using pg_basebackup. I was backing up a server that had no activityon it. The backup connected but no data was transferring, both ends sitting idle. It finally occurred to me totry a manual checkpoint and it then the backup took off and completed. According to 24.3 in the docs, pg_start_backup() performs a checkpoint. So I was surpassed that using the pg_baseback utilityI had to manual kick a checkpoint before the transfer would start. Is this correct behavior? alan fwiw, invocation: pg_basebackup -P --xlog —host=XXXXX --pgdata=pgsql --user=replicate
On Wed, Feb 5, 2014 at 9:15 AM, Alan Nilsson <anilsson@apple.com> wrote:
I tried (and finally succeeded) to do a base backup tonight using pg_basebackup. I was backing up a server that had no activity on it. The backup connected but no data was transferring, both ends sitting idle. It finally occurred to me to try a manual checkpoint and it then the backup took off and completed.
According to 24.3 in the docs, pg_start_backup() performs a checkpoint. So I was surpassed that using the pg_baseback utility I had to manual kick a checkpoint before the transfer would start.
Is this correct behavior?
The checkpoint that's started by both pg_basebackup and pg_start_backup() is by default a "spread checkpoint", which means we intentionally try to make it take longer, up to several minutes (depending on the value of checkpoint_completion_target). This is normally a good idea on a busy system, but can lead to these "interesting" results on those that are almost idle.
Running a manual CHECKPOINT always runs it in "fast" mode, which is checkpoint as quickly as possible, ignoring the setting of the completion target.
My guess is you just didn't wait long enough (typically checkpoint_completion_target * checkpoint_timeout or somewhere in that region) - if you had, it would've started the backup for you.
If you know your system is going to be mostly idle, you can instruct pg_basebackup to issue a fast checkpoint instead of the default one. Just add "-c fast" to the commandline options. There should never be a need to run a manual checkpoint.
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/