From: | Philip Warner <pjw(at)rhyme(dot)com(dot)au> |
---|---|
To: | Alfred Perlstein <bright(at)wintelcom(dot)net> |
Cc: | Jan Wieck <janwieck(at)Yahoo(dot)com>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Performance monitor signal handler |
Date: | 2001-03-16 01:20:04 |
Message-ID: | 3.0.5.32.20010316122004.04dc1100@mail.rhyme.com.au |
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Lists: | pgsql-hackers |
At 17:10 15/03/01 -0800, Alfred Perlstein wrote:
>>
>> Which is why the backends should not do anything other than maintain the
>> raw data. If there is atomic data than can cause inconsistency, then a
>> dropped UDP packet will do the same.
>
>The UDP packet (a COPY) can contain a consistant snapshot of the data.
>If you have dependancies, you fit a consistant snapshot into a single
>packet.
If we were going to go the shared memory way, then yes, as soon as we start
collecting dependant data we would need locking, but IOs, locking stats,
flushes, cache hits/misses are not really in this category.
But I prefer the UDP/Collector model anyway; it gives use greater
flexibility + the ability to keep stats past backend termination, and,as
you say, removes any possible locking requirements from the backends.
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