SQL re-parsing on query executed against a remote database using database links

From: Pentti <penttik_at_gmail.com>
Date: Fri, 14 Oct 2005 20:11:59 +0100
Message-ID: <tIednVS3f_OAns3eRVnyuw_at_eclipse.net.uk>

Can anyone help to understand why re-parsing occurs on a remote database
(using database links), even though we are using a prepared statement on
the local database:


We have an schema (s1) on an Oracle 9i database with database links pointing to a schema (s2) on another Oracle 9i database.

We have a SQL statement which joins tables from schemas s1 to tables in schema s2 by the use of database links (tablename_at_linkname). The query is executed against schema s1.

The SQL statement is prepared and re-executed over many iterations
(using bind variables - Java/jdbc). The statement is closed only when we
have completed the iterations.

For both databases, the optimizer mode is CHOOSE and ALL the tables have been analyzed.


We have found that when we monitor / analyse the database, the parsing rate is high, which is impacting the performance of the process.

NOTE: We also ran the same tests using Oracle 8i (for both databases) instead of 9i. In these tests the parsing rate was very low (zero). This is what I would have regarded as the expected behaviour.

The same high parsing rate is also seen when both schemas reside on the same database, and database links are used to join tables from the 2 schemas. If however, the SQL query is amended to refer to the remote tables in schema s2 by schema.tablename rather than tablename_at_linkname, then the parsing rate is again very low (as expected) and the process runs much more quickly. Received on Fri Oct 14 2005 - 21:11:59 CEST

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