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clog_buffers to 64 in 8.3?

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: pgsql-hackers(at)postgresql(dot)org
Subject: clog_buffers to 64 in 8.3?
Date: 2007-08-02 14:58:45
Message-ID: 200708020758.45997.josh@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-hackers
All,

Through the User Concurrency Thread on -performance [1], Tom and Jignesh found 
that our proximate bottleneck on SMP multi-user scaling is clog_buffers.  
Increasing clog_buffers to 64 improved this scaling by 30% per Jignesh:

===================

8.3+ HOT = did not defer more from 8.2 Numbers and hit the CLOG problem 
at 1100 users (instead of 1000 for 8.2)

8.3 + HOT + CLOG = Got a 1350 users peak of 137364 txn  and it held 
steady till 1450 before it started dropping..

The Best 8.2 +CLOG patch is at 1250user at 128638 txn.. which at the 
same users in 8.3 did 131265.. So per user transactions also seems to 
have improved.. Good but roughly 2% at same user count.. But peak value 
in terms of scalability the improvement is 6.7%

Pristine 8.2 could do about 950 users at 100828 txn: So at same user 
transactions 8.3+HOT+CLOG gives about  102058 txn =  1.2% while in terms 
of scalability throughput we get a huge boost of 36.2%

So if we get the CLOG patch integrated in 8.3+HOT+CLOG release then 
overall the gain from our pristine 8.2.4 release will be about  36%  out 
of the box ....

===================

So:

1) Is there any potential negative impact to increasing the number of CLOG 
buffers?

2) Is this a small enough change that we can make it during beta?

---Josh

[1] http://archives.postgresql.org/pgsql-performance/2007-07/msg00237.php

-- 
Josh Berkus
PostgreSQL @ Sun
San Francisco

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