Re: Lob chunk updates

From: Tanel Poder <tanel.poder.003_at_mail.ee>
Date: Wed, 17 Mar 2004 22:58:50 +0200
Message-Id: <200403172058.i2HKwoA01287@mail-fe75.tele2.ee>

> Anyone notice this? 50 concurrent updaters for a
> table's LOB stored out-of-line are serialized on
> the HW enqueue, unless truncated.

Because of read consistency reasons, Oracle never overwrites the lobchunk upon update, it stores a new copy in available space instead. The period how long the old copies are retained before can be overwritten by other transactions depends on your PCTVERSION or RETENTION settings on the lobsegment.

For a freshly created out-of-line lob this might cause lob segment growing (HWM increases = HW enqueue gets) upon first updates, but should stabilize after a while, when old chunks start to get overwritten.

If you're on 9i, start with checking RETENTION setting on your LOB segment.

Tanel.

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Received on Wed Mar 17 2004 - 14:56:31 CST