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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: Jaime Casanova <jcasanov(at)systemguards(dot)com(dot)ec>, pgsql-hackers(at)postgresql(dot)org, Robert Haas <robertmhaas(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Hans-Juergen Schoenig <postgres(at)cybertec(dot)at>, Josh Berkus <josh(at)agliodbs(dot)com>, Sándor Miglécz <sandor(at)cybertec(dot)at>, Andres Freund <andres(at)anarazel(dot)de>
Subject: Re: lock_timeout GUC patch
Date: 2010-01-13 21:26:57
Message-ID: 4B4E3AA1.8000701@cybertec.at (view raw or flat)
Thread:
Lists: pgsql-hackers
Boszormenyi Zoltan írta:
> Tom Lane írta:
>   
>> Boszormenyi Zoltan <zb(at)cybertec(dot)at> writes:
>>   
>>     
>>> Tom Lane írta:
>>>     
>>>       
>>>> If this patch is touching those parts of relcache.c, it probably needs
>>>> rethinking.
>>>>       
>>>>         
>>   
>>     
>>> What I did there is to check the return value of LockRelationOid()
>>> and also elog(PANIC) if the lock wasn't available.
>>> Does it need rethinking?
>>>     
>>>       
>> Yes.  What you have done is to change all the LockSomething primitives
>> from return void to return bool and thereby require all call sites to
>> check their results.  This is a bad idea.
>>     
>
> Okay, can you tell me how can I get the relation name
> out of the xid in XactLockTableWait()? There are several
> call site of this function, and your idea about putting the error
> code into the LockSomething() functions to preserve the API
> results strange error messages, like
>
> ERROR:  could not obtain lock on transaction with ID 658
>
> when I want to UPDATE a tuple in a session when
> this and another session have a FOR SHARE lock
> on said tuple.
>
>   
>>   There is no way that you can
>> ensure that all third-party modules will make the same change, meaning
>> that accepting this patch will certainly introduce nasty, hard to
>> reproduce bugs.  And what's the advantage?  The callers are all going
>> to throw errors anyway, so you might as well do that within the Lock
>> function and avoid the system-wide API change.
>>     

May I change the interface of XactLockTableWait()
and MultiXactIdWait()? Not the return value, only the number
of parameters. E.g. with the relation name, like in the attached
patch. This solves the problem of bad error messages...
What do you think?

>> I think this is a big patch with a small patch struggling to get out.
>>   
>>     
>
> Your smaller patch is attached, with the above strangeness. :-)
>
> 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
http://www.postgresql.at/


Attachment: 5-pg85-locktimeout-13-ctxdiff.patch
Description: text/x-patch (42.4 KB)

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