On 9/26/15 7:12 PM, Nikolai Zhubr wrote:
26.09.2015 20:59, Tom Lane wrote:
[...]
A session-end hook seems pretty problematic to me: you simply cannot
guarantee that it will run at all. (Consider process crash or server
abort cases.) So anything built on the assumption that it gets to run
at session end is going to be inherently unreliable.
Yes, I understand that.
For such cases (of e.g. abnormal shutdown) it would also be nice if a
database could 'autorun' some specified function just after server has
performed whetever startup/replay/cleanup procedures necessary and
immediately before it is ready for normal operation. This would allow to
perform some checks and cleanups to restore consistency. And actually,
such 'autorun' function could be interesting regardless of this session
begin/end thing.
And there are already quite some hooks in use for session-end cleanups
at C-level, like e.g. for disposing temp tables, just none of them
expose anything to SQL level. I'd guess this technique is available for
use by extensions, so potentially SQL-level hook could also be
implemented. Though I think it is a bit beyond my capability at the
moment...
Actually, there's probably some other hooks you could use for this purpose.
BTW, if you want to extend Pavel's code to also handle logout, you just
need to create a _PG_fini function. See the end of this section in the
docs: http://www.postgresql.org/docs/9.4/static/xfunc-c.html#XFUNC-C-DYNLOAD
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Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
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