Re: [PATCH] Refactoring of LWLock tranches

From: Ildus Kurbangaliev <i(dot)kurbangaliev(at)postgrespro(dot)ru>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, "andres(at)anarazel(dot)de" <andres(at)anarazel(dot)de>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Subject: Re: [PATCH] Refactoring of LWLock tranches
Date: 2015-11-16 12:32:45
Message-ID: 20151116153245.40d7f22855ac336eb9c0ee0e@postgrespro.ru
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On Sun, 15 Nov 2015 16:24:24 -0500
Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> > I have some questions about next steps on other tranches.
> > First of all, I think we can have two API calls, something like:
> >
> > 1) LWLockRequestTranche(char *tranche_name, int locks_count)
> > 2) LWLockGetTranche(char *tranche_name)
> >
> > LWLockRequestTranche reserve an item in main tranches array in shared memory, and
> > allocates space for name, LWLockTranche and LWLocks. There is first question. It is
> > ok if this call will be from *ShmemSize functions? We keep those requests,
> > calculate a required size in LWLockShmemSize (by moving this call to the end)
> > and create all these tranches in CreateLWLocks.
>
> I think what we should do about the buffer locks is polish up this
> patch and get it applied:
>
> http://www.postgresql.org/message-id/20150907175909.GD5084@alap3.anarazel.de
>
> I think it needs to be adapted to use predefined constants for the
> tranche IDs instead of hardcoded values, maybe based on the attached
> tranche-constants.patch. This approach could be extended for the
> other stuff in the main tranche, and I think that would be cleaner
> than inventing LWLockRequestTranche as you are proposing. Just make
> the tranche IDs constants, and then the rest fits nicely into the
> framework we've already got.

What if just create a control struct in shared memory like in other places? BufferDescriptors
and BufferBlocks can be kept there along with tranches definitions
and lwlocks. Buffer locks that are located in MainLWLockArray by offset
can be moved there too.

--
Ildus Kurbangaliev
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company

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