RE: Urgent: db file sequential read - wait
- From: "Lex de Haan" <lex.de.haan@xxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 31 Mar 2004 19:49:35 +0200
Hi Stefan,
not exactly giving you an answer, but this DELETE statement with a
correlated subquery to the table itself is pretty expensive. maybe you can
rewrite it into a DELETE on an updatable view instead? something like:
SQL> DELETE FROM ( some smart self-join expression goes here ) WHERE ... ;
that might kill two birds with a single stone: better performance, and wait
problem solved ...
Cheers,
Lex.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Stefan Jahnke
Sent: Wednesday, March 31, 2004 18:34
To: Oracle DBA List (E-Mail)
Subject: Urgent: db file sequential read - wait
Hi list
I have a session waiting forever on a "db file sequential read" wait event
during a mass delete.
The statement looks like this:
DELETE
FROM tcdhispersversnr a
WHERE EXISTS
(SELECT idvistamaster
FROM tcdhispersversnr b
WHERE b.pkfk = a.pkfk
AND b.idvistamaster = a.idvistamaster
AND a.idvistadetail IS NULL
AND b.idvistadetail IS NOT NULL
AND (
(CAST(A.ZHI_SYSEINDAT AS TIMESTAMP(0)) >=
CAST(B.ZHI_SYSEINDAT AS TIMESTAMP(0))
AND
CAST(A.ZHI_SYSEINDAT AS TIMESTAMP(0)) <
CAST(B.ZHI_SYSERSDAT AS TIMESTAMP(0)))
OR
(CAST(B.ZHI_SYSEINDAT AS TIMESTAMP(0)) >=
CAST(A.ZHI_SYSEINDAT AS TIMESTAMP(0))
AND
CAST(B.ZHI_SYSEINDAT AS TIMESTAMP(0)) <
CAST(A.ZHI_SYSERSDAT AS TIMESTAMP(0)))
)
AND (
(A.ZHI_SYSGUADAT >= B.ZHI_SYSGUADAT
AND
A.ZHI_SYSGUADAT < B.ZHI_SYSGUBDAT)
OR
(B.ZHI_SYSGUADAT >= A.ZHI_SYSGUADAT
AND
B.ZHI_SYSGUADAT < A.ZHI_SYSGUBDAT)
)
)
The block the session is waiting for belongs to an index on table
tcdhispersversnr. I was thinking it might be a problem that the index is
updated by the delete part of the statement while the sub-select part of the
statement uses the index. Both the table in the delete-part and the table
being queried in the sub-select are the same.
NOTHING else is happening on this machine. No locks or latches or memory or
undo problems whatsoever.
Anybody any idea what might cause that problem?
At totally frustrated yours,
Stefan
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