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Multiple copies of the same block in the buffer cache

From: Vsevolod Afanassiev <vafanassiev_at_aapt.com.au>
Date: 25 Mar 2002 22:55:00 -0800
Message-ID: <4f7d504c.0203252255.1b8cc83b@posting.google.com>


When I look in V$CACHE I often see multiple (2-6) copies of the same block. Yes, I know that V$CACHE is an Oracle Parallel Server view, and it is not even created by default during installation. However, many people told me that V$CACHE is perfectly valid for non-OPS instances. What really puzzles me is that there are multiple copies of the same block even for the table that is queried/updated by only one session.

Also, I noticed that the total number of rows in V$CACHE is slightly different from db_block_buffers. For example, I have db_block_buffers = 350,000 (database with 2K blocks) and select count(*) from v$cache returns 362,971. It may be a coincidence, but the difference between these two numbers (12,971) is approx. half of the total number of blocks with more that one copy (25,060). Received on Tue Mar 26 2002 - 00:55:00 CST

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