Re: lock_timeout GUC patch

Boszormenyi Zoltan írta:
> Tom Lane írta:
>
>> Greg Stark <stark(at)mit(dot)edu> writes:
>>
>>
>>> we already have statement timeout it seems the natural easy to implement
>>> this is with more hairy logic to calculate the timeout until the next of the
>>> three timeouts should fire and set sigalarm. I sympathize with whoever tries
>>> to work that through though, the logic is hairy enough with just the two
>>> variables...but at least we know that sigalarm works or at least it had
>>> better...
>>>
>>>
>> Yeah, that code is ugly as sin already. Maybe there is a way to
>> refactor it so it can scale better? I can't help thinking of Polya's
>> inventor's paradox ("the more general problem may be easier to solve").
>>
>> If we want to do it without any new system-call dependencies I think
>> that's probably the only way. I'm not necessarily against new
>> dependencies, if they're portable --- but it seems these aren't.
>>
>>
>
> Okay, after reading google it seems you're right that OS X lacks
> sem_timedwait(). How about adding a configure check for semtimedop()
> and sem_timedwait() and if they don't exist set a compile time flag
> (HAVE_XXX) and in this case PGSemaphoreTimedLock() would
> behave the same as PGSemaphoreLock() and have an assign_*()
> function that tells the user that the timeout functionality is missing?
> We have precedent for the missing functionality with e.g.
> effective_io_concurrency and ereport() is also allowed in such
> functions, see assign_transaction_read_only().
>

Attached with the proposed modification to lift the portability concerns.
Fixed the missing check for get_rel_name() and one typo ("transation")
Introduced checks for semtimedop() and sem_timedwait() in configure.in
and USE_LOCK_TIMEOUT in port.h depending on
HAVE_DECL_SEMTIMEDOP || HAVE_DECL_SEM_TIMEDWAIT || WIN32
Introduced assign_lock_timeout() GUC validator function that allows
setting the value only from the wired-in-default (0) or from SET statements.

Comments?

Best regards,
Zoltán Böszörményi

--
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Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
http://www.postgresql.at/