Message-ID: <53F46DA9.9020609@vmware.com>
Date: Wed, 20 Aug 2014 12:43:05 +0300
From: Heikki Linnakangas <hlinnakangas@vmware.com>
Organization: VMware
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To: Andres Freund <andres@2ndquadrant.com>,
 Robert Haas <robertmhaas@gmail.com>
CC: Tom Lane <tgl@sss.pgh.pa.us>, Peter Geoghegan <pg@heroku.com>, Pg Hackers
 <pgsql-hackers@postgresql.org>, Ants Aasma <ants@cybertec.at>
Subject: Re: better atomics - v0.5
References: 
 <CA+TgmoYBW+ux5-8Ja=Mcyuy8=VXAnVRHp3Kess6Pn3DMXAPAEA@mail.gmail.com>
 <20140625171434.GG24114@awork2.anarazel.de>
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Hi Andres,

Are you planning to continue working on this? Summarizing the discussion 
so far:

* Robert listed a bunch of little cleanup tasks 
(http://www.postgresql.org/message-id/CA+TgmoZShVVqjaKUL6P3kDvZVPibtgkzoti3M+Fvvjg5V+XJ0A@mail.gmail.com). 
Amit posted yet more detailed commends.

* We talked about changing the file layout. I think everyone is happy 
with your proposal here: 
http://www.postgresql.org/message-id/20140702131729.GP21169@awork2.anarazel.de, 
with an overview description of what goes where 
(http://www.postgresql.org/message-id/CA+TgmoYuxfsm2dSy48=JgUTRh1mozrvmjLHgqrFkU7_WPV-xLA@mail.gmail.com)

* Talked about nested spinlocks. The consensus seems to be to (continue 
to) forbid nested spinlocks, but allow atomic operations while holding a 
spinlock. When atomics are emulated with spinlocks, it's OK to acquire 
the emulation spinlock while holding another spinlock.

* Talked about whether emulating atomics with spinlocks is a good idea. 
You posted performance results showing that at least with the patch to
use atomics to implement LWLocks, the emulation performs more or less 
the same as the current spinlock-based implementation. I believe 
everyone was more or less satisfied with that.


So ISTM we have consensus that the approach to spinlock emulation and 
nesting stuff is OK. To finish the patch, you'll just need to address 
the file layout and the laundry list of other little details that have 
been raised.

- Heikki


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