Re: [PATCH] Refactoring of LWLock tranches

On Sat, Dec 12, 2015 at 1:17 PM, andres(at)anarazel(dot)de <andres(at)anarazel(dot)de> wrote:
> On 2015-11-15 16:24:24 -0500, Robert Haas wrote:
>> 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.
>
> Here's two patches doing that. The first is an adaption of your
> constants patch, using an enum and also converting xlog.c's locks. The
> second is the separation into distinct tranches.

Personally, I prefer the #define approach to the enum, but I can live
with doing it this way. Other than that, I think these patches look
good, although if it's OK with you I would like to make a pass over
the comments and the commit messages which seem to me that they could
benefit from a bit of editing (but not much substantive change).

> One thing to call out is that an "oversized" s_lock can now make
> BufferDesc exceed 64 bytes, right now that's just the case when it's
> larger than 4 bytes. I'm not sure if that's cause for real concern,
> given that it's not very concurrent or ancient platforms where that's
> the case.
> http://archives.postgresql.org/message-id/20150915020625.GI9666%40alap3.anarazel.de
> would alleviate that concern again, as it collapses flags, usage_count,
> buf_hdr_lock and refcount into one 32 bit int...

I don't think that would be worth worrying about even if we didn't
have a plan in mind that would make it go away again, and even less so
given that we do have such a plan.

--
Robert Haas
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