On 07/11/2016 06:53 AM, Craig Ringer wrote:
On 11 July 2016 at 11:49, Michael Paquier <michael.paqu...@gmail.com <mailto:michael.paqu...@gmail.com>> wrote:On Mon, Jul 11, 2016 at 3:36 AM, Julien Rouhaud <julien.rouh...@dalibo.com <mailto:julien.rouh...@dalibo.com>> wrote: > I'm not opposed, but in this case we should also provide a proper > documentation of all the required actions to mimick normal backends. I'd rather just add a note like "Have a look at PostgresMain if you want to imitate a backend able to run queries!" instead of listing all the actions doable. If low-level things are added or removed in the future in PostgresMain, it is very likely that the documentation will not be updated at the same time, killing its purpose at the end. That sounds like a bug breeding ground. Especially with extensions whose bgworkers operate across Pg versions, extensions that get updated without re-checking PostgresMain and don't notice some new housekeeping task, etc. Rather than encouraging every extension author to copy and paste random chunks of PostgresMain, probably incorrectly, I really think factoring the required logic out into something reusable by bgworkers is going to be the way to go.
I'm not sure I agree with this. Clearly, the fact that worker_spi does not invoke pgstat_report_stat() is a bug, but as Michael points out, we don't have much insight into what is happening in bgworkers.
Following the changes in PostgresMain() - particularly if your bgworker needs to support multiple versions - is difficult, sure. But well, if you decided to implement a bgworker operating at such low level, you voluntarily accepts that responsibility.
That does not mean we can't make that easier. For example, what about extending the bgworker API with
(a) a set of flags (similar to bgw_flags) identifying which maintenance tasks the bgworker requests, and
(b) a BackgroundWorkerCleanup() function the bgworker might place at a suitable place, invoking all the requested maintenance tasks?
Sure, this may only help for bgworkers that do stuff fairly close to regular backends, but maybe that's enough.
In any case, I think adding the pgstat_report_stat() into worker_spi seems like a reasonable (and backpatchable) fix.
regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
