13.2.1 Points to be checked before performing tuning
This subsection describes the points to be checked before performing the tuning to reduce the execution time of SQL statements and commands. Please review the following two points:
- Revise the data DB areas that store base tables and indexes
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Make sure that the following conditions are met:
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One data DB area stores only one base table.
For details about how to check the base table (or base tables) stored in a data DB area, see (14) When identifying the table name of a table stored in a DB area in B.22 Searching a dictionary table.
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One data DB area stores only one index.
For details about how to check the index (or indexes) stored in a data DB area, see (15) When identifying the index name of an index stored in a DB area in B.22 Searching a dictionary table.
As described in 5.6.1 Points to consider when designing a data DB area, if multiple base tables or indexes are stored in one data DB area, the resulting increase in I/O accesses might degrade performance. Especially, do not store both a row store table and column store table in one data DB area. To avoid this, make sure that no more than one base table or index is stored in a data DB area.
For details about how to revise the data DB areas that store base tables and indexes, see 11.1.14 Changing the data DB area that stores a base table and 11.3.8 Changing the data DB area that stores indexes.
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- Revise the global buffers to be allocated to data DB areas
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Check whether one global buffer is exclusively allocated to one data DB area. To check the global buffer (or global buffers) allocated to a data DB area, use the adbls -d gbuf command. For details about the adbls -d gbuf command, see adbls -d gbuf (Display Global Buffer Information) in the manual HADB Command Reference.
Allocating one global buffer to multiple data DB areas might degrade performance. Therefore, make sure that each global buffer is allocated to only one data DB area. To revise the global buffers, check and, if necessary, revise each adbbuff operand specification in the server definition. For details about the adbbuff operand in the server definition, see 7.2.11 Operands and options related to global buffers (command format). For details about how to modify the server definition, see 8.5.2 Modifying the server definition.