Re: Determine sequence cache size in RAC
----- Original Message ----- ]From: "CRISLER, JON A (ATTCORP)" <JC1706@xxxxxxx> 
]To: <denis.sun@xxxxxxxxx>; <oracle-l@xxxxxxxxxxxxx>
]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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