Message-ID: <C7796B933F3E488190183C20725D13BA@Primary>
From: "Jonathan Lewis" <jonathan@jlcomp.demon.co.uk>
To: <JC1706@att.com>, <denis.sun@yahoo.com>, <oracle-l@freelists.org>
References: <986379.16870.qm@web161805.mail.bf1.yahoo.com> <9F15274DDC89C24387BE933E68BE3FD3043170@MISOUT7MSGUSR9D.ITServices.sbc.com>
Subject: Re: Determine  sequence cache size in RAC
Date: Thu, 5 May 2011 13:46:42 +0100
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----- Original Message ----- 
]From: "CRISLER, JON A (ATTCORP)" <JC1706@att.com>
]To: <denis.sun@yahoo.com>; <oracle-l@freelists.org>
]Sent: Monday, May 02, 2011 11:14 PM
]Subject: RE: Determine sequence cache size in RAC
]

]Values of 1000 to 10000 have worked well for me :)  This was derived from trial 
and error.
]

That makes sense.

Each index entry will take about 15 or 16 bytes - giving about 520 entries per 
index leaf block.

A side effect of RAC means that the index leaf blocks will be doing 50/50 splits 
leaving you with about 260 entries per block.

This means at a cache size of 1,000 an instance will fill about 4 leaf blocks 
before refreshing the cache and colliding briefly on the top leaf block with the 
previous instance holding the highest cache value.  At a cache size of 10,000 
that will be about 40 blocks for an instance before a collision.

The more instances you have, the larger the cache needs to be.


Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com

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