Re: Determine sequence cache size in RAC
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <JC1706@xxxxxxx>, <denis.sun@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 5 May 2011 13:46:42 +0100
----- 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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