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| MQSI_EMPTY_DB_CACHE=Y |
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| seeknee |
 Posted: Fri Jul 09, 2004 3:04 am Post subject: MQSI_EMPTY_DB_CACHE=Y |
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Apprentice
Joined: 08 Aug 2002
Posts: 41
Location: Melbourne, Australia
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Hi All
Could someone please give me a little more information on what this command does.
Thanks |
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| JT |
| Posted: Fri Jul 09, 2004 5:39 am Post subject: |
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Padawan
Joined: 27 Mar 2003
Posts: 1564
Location: Hartford, CT.
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When a SQL statement is issued within a message flow, it is prepared using the SQLPrepare function. The statement and associated handle are cached, which leads to better performance for subsequent executions of the SQL statement.
The MQSI_EMPTY_DB_CACHE setting disables the caching of these statements beyond the processing of the current message. |
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| kirani |
| Posted: Sat Jul 10, 2004 10:14 am Post subject: |
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Jedi Knight
Joined: 05 Sep 2001
Posts: 3779
Location: Torrance, CA, USA
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Can anyone cofirm that,
1. This variable is supported in WMQI 2.1?
2. Does this affect cache generated by PASSTHRU statement only?
_________________
Kiran
IBM Cert. Solution Designer & System Administrator - WBIMB V5
IBM Cert. Solutions Expert - WMQI
IBM Cert. Specialist - WMQI, MQSeries
IBM Cert. Developer - MQSeries
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| JT |
| Posted: Sat Jul 10, 2004 6:39 pm Post subject: |
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Padawan
Joined: 27 Mar 2003
Posts: 1564
Location: Hartford, CT.
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| Quote: |
| 1. This variable is supported in WMQI 2.1? |
See the following IBM posting regarding references to the MQSI_EMPTY_DB_CACHE environment setting for WMQI v2.1:
http://www-1.ibm.com/support/docview.wss?uid=swg1IY41636
| Quote: |
| 2. Does this affect cache generated by PASSTHRU statement only? |
According to the following WBIMB excerpt (Dealing with Problems/Problems when developing message flows) it appears the environment setting applies not only to SQL commands issued via the PASSTHRU command but also to those SQL commands that are not:
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When a database call is made from within a message flow node, the flow constructs the appropriate SQL, and this is sent using ODBC to the database manager. As part of this process, the SQL statement is prepared using the SQLPrepare function, and a statement handle is acquired so that the SQL statement can be executed.
For performance reasons, after the statement is prepared, the statement and handle are saved in a cache to reduce the number of calls to the SQLPrepare function. If the statement is already in the cache, the statement handle is returned so that it can be re-executed with newly bound parameters.
The statement string is used to perform the cache lookup. By using hardcoded SQL strings that differ slightly for each message, the statement is not found in the cache, and an SQLPrepare function is always performed (and a new ODBC cursor is opened). When using PASSTHRU statements, use parameter markers so that the same SQL prepared statement can be used for each message processed, with the parameters being bound at runtime. This approach is more efficient in terms of database resources and, for statements that are repeatedly executed, it is faster. |
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