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Re: Proposal for Allow postgresql.conf values to be changed via SQL [review]

From: Boszormenyi Zoltan <zb(at)cybertec(dot)at>
To: Amit kapila <amit(dot)kapila(at)huawei(dot)com>
Cc: 'Tom Lane' <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 'Robert Haas' <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Proposal for Allow postgresql.conf values to be changed via SQL [review]
Date: 2013-01-05 08:37:08
Message-ID: 50E7E634.9000603@cybertec.at (view raw or flat)
Thread:
Lists: pgsql-hackers
2013-01-05 05:58 keltezéssel, Amit kapila írta:
> On Friday, January 04, 2013 10:57 PM Boszormenyi Zoltan wrote:
>> Hi,
>> I am reviewing your patch.
> Thank you very much.
>
>> Since you are using a constant string, it would be a little faster
>> to use "sizeof(string)-1" as it can be computed at compile-time
>> and not run the strlen() all the time this code is reached.
> I have reffered the code just above for PG_TEMP_FILE_PREFIX in same function sendDir().
> I have that not only that place, but there other places where strlen is used for PG_TEMP_FILE_PREFIX.
> I think in this path, such optimization might not help much.
> However if you think we should take care of this, then I can find other places where similar change can be done
> to make it consistent?

Yes, but it needs a separate cleanup patch.

Also, since the SET PERSISTENT patch seems to create a single lock file,
sizeof(string) (which includes the 0 byte at the end of the string, so it
matches the whole filename) can be used instead of strlen(string) or
sizeof(string)-1 that match the filename as a prefix only.

>
>> In create_conf_lock_file():
>
>> Can't we add a new LWLock and use it as a critical section instead
>> of waiting for 10 seconds? It would be quite surprising to wait
>> 10 seconds  when accidentally executing two SET PERSISTENT
>> statements in parallel.
> Yes, you are right adding a new LWLock will avoid the use of sleep.
> However I am just not sure if for only this purpose we should add a new LWLock?
>
> Similar logic is used in CreateLockFile() for postmaster file but it doesn't use sleep.
> How about reducing the time of sleep or removing sleep, in that user might get
> error and he need to retry to get his command successful?
>
> With Regards,
> Amit Kapila.
>


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Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
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Subject: Re: Proposal for Allow postgresql.conf values to be changed viaSQL [review]
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