Re: Query on all_tables taking long time
- From: Nigel Thomas <nigel_cl_thomas@xxxxxxxxx>
- To: Harvinder.Singh@xxxxxxxxxxxxx, oracle-l <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 9 May 2007 14:30:16 -0700 (PDT)
Harvinder
The predicate doesn't allow indexed access. And remember ALL_TABLES is a
(complex) view. The name of the owner is stored in USER$, the name of the
object in OBJ$. So the CBO (in effect) builds the entire ALL_TABLES view and
trawls through it matching the predicate.
Rewrite the predicate as:
WHERE OWNER = :b1
AND TABLE_NAME = :b2
Now you're giving the CBO the chance to decide whether to drive off OWNER or
off TABLE_NAME
HTH
Regards Nigel
----- Original Message ----
From: Harvinder Singh <Harvinder.Singh@xxxxxxxxxxxxx>
To: oracle-l <oracle-l@xxxxxxxxxxxxx>
Sent: Wednesday, May 9, 2007 9:17:52 PM
Subject: Query on all_tables taking long time
Hi,
We have a function that checks if the table exists in current schema if
specified without the schema name or all_tables if we specify the table
name as object_name.table_name and it looks like query against
all_tables is running very slow. Following is the output from the tkprof
and it is not clear why optimizer is using 18 sec for cpu and doing 134k
reads. This is 10.2.0.1 on RHAT ENT 4
SELECT COUNT(1)
FROM
ALL_TABLES WHERE OWNER || '.' || TABLE_NAME = UPPER(:B1 )
call count cpu elapsed disk query current
rows
------- ------ -------- ---------- ---------- ---------- ----------
----------
Parse 158 0.02 0.02 0 0 0
0
Execute 158 0.04 0.03 0 0 0
0
Fetch 158 17.99 17.88 0 134540 0
158
------- ------ -------- ---------- ---------- ---------- ----------
----------
total 474 18.06 17.93 0 134540 0
158
Misses in library cache during parse: 0
Optimizer mode: ALL_ROWS
Parsing user id: 172 (recursive depth: 1)
Thanks
--Harvinder
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