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From: Paul M. Aoki <aoki@CS.Berkeley.EDU>
To: Andrew K. Yu <andrew@postgres.Berkeley.EDU>
Cc: Sunita Sarawagi <sunita@postgres.Berkeley.EDU>
Cc: postgres-arch@postgres.Berkeley.EDU
Subject: Re: sunita's bufmgr bug
Date: Wed, 08 Mar 95 21:47:45 -0800
Message-ID: <199503090547.VAA19140@faerie.CS.Berkeley.EDU> (raw)
In-Reply-To: <199503082333.PAA00124@eden.CS.Berkeley.EDU>

"Andrew K. Yu" <andrew@postgres.Berkeley.EDU> writes:
> hey Paul, we seem to have found the bug (that you introduce last
> July while you're optimizing the bufmgr).

look carefully at the rcs history.

the last two revisions strictly increased the amount of code covered
by mutexes.  for example, the tag operations in BufferReplace weren't
mutexed at all before the last revision.  this sort of worked on suns
but didn't work so well on alphas because of their memory consistency
model.

the business of giving up the mutex in BufferAlloc before calling
BufferReplace has *always* been there.  look at any previous revision.
the OPTIMIZE_SINGLE business is something that i added that *avoids*
giving up the mutex during the i/o when defined (evidently the more
correct behavior anyway, oh well) because semop(3) is so expensive
under ultrix (no TASlocks).  without -DOPTIMIZE_SINGLE, BufferAlloc
has the same behavior that was there for the last 83 revisions. 
--
  Paul M. Aoki          |  University of California at Berkeley
  aoki@CS.Berkeley.EDU  |  Dept. of EECS, Computer Science Division (#1776) 
                        |  Berkeley, CA 94720-1776

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  Subject: Re: sunita's bufmgr bug
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