Re: Confused about max_standby_streaming_delay

[Jeff Janes <jeff.janes@xxxxxxxxx>]

On Wed, Sep 6, 2017 at 9:43 AM, Robert Inder <robert@xxxxxxxxxxxxxxxxx> wrote:

... 

And I've read that the answer to this is to set max_standby_streaming_delay in postgresql94.conf.

So I've set it to "600s" -- ten minutes. 

I thought this would mean that when there was a conflict with an update from the live server, Postgres would give the dump 10 minutes "grace" in which to finish before killing it.

Ten minutes may or may not be enough.  But in a case where it isn't enough, and the dump is abandonned, I would expect to see something like

    the dump of database_a finishing at 5 minutes past the hour,

    the dump of database_b

          starting after the dump of database_a,

          having a conflict,

          being given 10 minutes to complete, and then

          being abandonned

    the dump of database_c starting after the dump of database_b and finishing (say) 3 minutes later

So the dump of database_c should finish at around 18 minutes past the hour.

BUT that is not what I am seeing.

On occasions where the dump of database_b is being abandonned, the successful dump of

database_c is timestamped less than 10 minutes after the dump of database_a

Which does not fit with the dump of database_b being given 10 minutes in which to finish

Have I misunderstood something?  Or is Postgres not actually configured the way I think it is?

The standby will wait for ten minutes to obtain the lock it wishes to obtain.  In 9.4, if something other than dump of database b was already blocking it for 8 minutes before the dump starts, then the dump of database b will only have 2 minutes, not 10, before it gets cancelled.  So, are there any long running jobs in database b other than the pg_dump?

 

Cheers,

Jeff