Re: lock_timeout GUC patch

From: Boszormenyi Zoltan <zb(at)cybertec(dot)at>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Greg Stark <stark(at)mit(dot)edu>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org, Jaime Casanova <jcasanov(at)systemguards(dot)com(dot)ec>
Subject: Re: lock_timeout GUC patch
Date: 2010-01-20 12:11:47
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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
and USE_LOCK_TIMEOUT in port.h depending on
Introduced assign_lock_timeout() GUC validator function that allows
setting the value only from the wired-in-default (0) or from SET statements.


Best regards,
Zoltán Böszörményi

Bible has answers for everything. Proof:
"But let your communication be, Yea, yea; Nay, nay: for whatsoever is more
than these cometh of evil." (Matthew 5:37) - basics of digital technology.
"May your kingdom come" - superficial description of plate tectonics

Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH

Attachment Content-Type Size
5-pg85-locktimeout-16-ctxdiff.patch text/x-patch 37.4 KB

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