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Re: Physical reads on Tables cached in KEEP_POOL

From: Sybrand Bakker <postbus_at_sybrandb.demon.nl>
Date: Fri, 25 Feb 2005 22:07:38 +0100
Message-ID: <ul4v11pmruk1lc0kabal6gh0sv2uub5ccf@4ax.com>


On 25 Feb 2005 12:14:36 -0800, "Gordon" <gordon_t_wu_at_yahoo.com> wrote:

>Hello,
>
>
>
>I'm getting a bouch of physical reads from a table that has been put
>into the KEEP pool. I've check that the KEEP pool does have sufficient
>memory to hold the tables cached in them.
>
>>From Statspack I see the SQLs causing physical reads are INSERT
>statements. Why does INSERT statements perform physical reads on
>tables that have been cached in KEEP pool? I'd think it would only
>need to perform physical writes.
>
>I'm running Oracle 10g on SUSE Enterprise 9
>
>Thanks

First of all: the KEEP pool only guarantees the data is on the cold end of the LRU list. The KEEP pool itself is not excluded from the LRU algorithm.

Secondly: a client session NEVER issues a physical write. Physical writes are handled by the DBWR. Clients only perform logical writes in the buffer cache

Thirdly: INSERTS may cause index blocks to be reorganized. If the index blocks aren't cached they would need to be read prior to being modified.

--
Sybrand Bakker, Senior Oracle DBA
Received on Fri Feb 25 2005 - 15:07:38 CST

Original text of this message

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