JDBC Type 4 Driver Programmer's Reference for SQL/MX Release 3.1 (H06.23+, J06.12+)

JDBC T4 applications experiencing high memory swapping can benefit from reducing the driver side cache and enabling MFC. Reduce the
driver side cache and enable MFC in the scenarios, where the MXOSRVR process exceeds 1 GB in size frequently.
For JDBC T4 applications where the large number of MXOSRVR processes is configured per processor, enable MFC to reduce swapping.
The other option is to increase the physical memory per processor to reduce swapping.
MFC combined with limited driver side cache is recommended for JDBC T4 applications, where the number of distinct queries is not known
or not fixed.
MFC Tuning Recommendations
When the number of connections required to be configured per processor is high in number (for example, more than 20 connections per
processor), use MFC for less memory utilization.
If an application has a small number of OLTP queries (such as, JOE) where there is no memory pressure and memory pressure is heavy
in execute() and fetch(), the MFC performance result will be close to that of the T4 driver cache with MFC consuming lesser
memory. In such applications, when a small number of connections are configured per processor, configure only the JDBC T4 driver
cache because there is no major difference between MFC and the T4 driver cache.
For applications with small number of queries, Driver Side Cache (DSC) provides better response time. For applications that have
a large number of queries, use a combination of DSC and MFC, which results in better memory usage and similar response time of
DSC. For typical applications, find the number of most frequently used statements and configure them as DSC and the rest as
MFC. If the most frequently used statements number is not known, it is recommended that you configure a number closer to 60%
of total queries in the application.
For example, if the application has 1000 unique queries, configure DSC (t4sqlmx.maxStatements) to 600. The
applications with more number of queries configured in the DSC, cause memory swap. Therefore, reduce the DSC number
and increase the queries in the MFC.
The JDBC/T4 driver, in memory, caches the most frequently used statements. The MXOSRVR, on the NonStop host,
caches the infrequent queries using MFC.
MFC Limitations
MFC is not a replacement for the JDBC T4 Driver Side Cache (DSC); the JDBC T4 driver side cache has a better response time than
MFC.
For more information on MFC limitations, see the HP
NonStop SQL/MX Connectivity Service Manual.
Statement Caching
If the statement caching feature is enabled, the JDBC T4 driver will cache the SQL statements, which use the scalar functions with a
higher number so that the statements are not removed from the cache. For information on statement caching, see
maxStatements
Property.
If the statement caching feature is not enabled or if there is no place in the JDBC T4 driver cache and the SQL statement to be prepared
uses a scalar function, the JDBC T4 driver will not permit the server side to use MFC while preparing this statement. For information on
MFC limitations, see the HP
NonStop SQL/MX Connectivity Service Manual. The scalar functions that are not supported by MFC are in
Appendix B. Scalar Functions.
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