Re: On login trigger: take three

On 20.12.2020 10:04, Pavel Stehule wrote:
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> čt 17. 12. 2020 v 19:30 odesílatel Pavel Stehule
> <pavel(dot)stehule(at)gmail(dot)com <mailto:pavel(dot)stehule(at)gmail(dot)com>> napsal:
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>
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> čt 17. 12. 2020 v 14:04 odesílatel Konstantin Knizhnik
> <k(dot)knizhnik(at)postgrespro(dot)ru <mailto:k(dot)knizhnik(at)postgrespro(dot)ru>> napsal:
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>
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> On 17.12.2020 9:31, Pavel Stehule wrote:
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>> st 16. 12. 2020 v 20:38 odesílatel Pavel Stehule
>> <pavel(dot)stehule(at)gmail(dot)com <mailto:pavel(dot)stehule(at)gmail(dot)com>>
>> napsal:
>>
>> Attached please find new versoin of the patch based on
>> on_connect_event_trigger_WITH_SUGGESTED_UPDATES.patch
>>
>> So there is still only
>> "disable_client_connection_trigger" GUC? because we
>> need possibility to disable client connect triggers
>> and there is no such need for other event types.
>>
>> As you suggested  have added "dathaslogontriggers"
>> flag which is set when client connection trigger is
>> created.
>> This flag is never cleaned (to avoid visibility
>> issues mentioned in my previous mail).
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>>
>> This is much better - I don't see any slowdown when logon
>> trigger is not defined
>>
>> I did some benchmarks and looks so starting language
>> handler is relatively expensive - it is about 25% and
>> starting handler like event trigger has about 35%. But
>> this problem can be solved later and elsewhere.
>>
>> I prefer the inverse form of disable_connection_trigger.
>> Almost all GUC are in positive form - so
>> enable_connection_triggger is better
>>
>> I don't think so current handling dathaslogontriggers is
>> good for production usage. The protection against race
>> condition can be solved by lock on pg_event_trigger
>>
>>
>> I thought about it, and probably the counter of connect
>> triggers will be better there. The implementation will be
>> simpler and more robust.
>>
>>
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> I prefer to implement different approach: unset
> dathaslogontriggers  flag in event trigger itself when no
> triggers are returned by EventTriggerCommonSetup.
> I am using double checking to prevent race condition.
> The main reason for this approach is that dropping of triggers
> is not done in event_trigger.c: it is done by generic code for
> all resources.
> It seems to be there is no right place where decrementing of
> trigger counters can be inserted.
> Also I prefer to keep all logon-trigger specific code in one file.
>
> Also, as you suggested, I renamed disable_connection_trigger
> to enable_connection_trigger.
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> New version of the patch is attached.
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> yes, it can work
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> for complete review the new field in pg_doc should be documented
>

Done.
Also I fixed some examples in documentation which involves pg_database.

--
Konstantin Knizhnik
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