12.2.4 Operands related to FETCH
- 11) pd_hb_ary_fec_num = rows-to-be-fetched-at-once-with-FETCH-facility-that-uses-array
<unsigned integer>((1-30000))- Specifies the number of rows to be fetched at one time with FETCH that uses an array.
- If the number of search result rows from a foreign table can be predicted to some degree, specify this operand. The communication overhead between HiRDB and the foreign server can be expected to decrease. For the SQL execution time and the number of FETCH operations to a foreign table based on the array FETCH count to the foreign server, check the statistical information related to foreign server usage. For details on the statistical information related to foreign server usage, see the Statistics analysis utility in the manual HiRDB Version 8 Command Reference.
- If this operand is omitted, HiRDB determines automatically a value that is optimized for the HiRDB processing.
- Specification guidelines
- If the specification value is too small, the number of communications between HiRDB and the foreign server increases, resulting in a greater overhead.
- If the specification value is too large, too large a memory area is used, resulting in a memory resource shortage.
- If the number of search result rows from a foreign table varies depending on the job, Hitachi recommends that this operand be omitted. Whether omitting this operand is advantageous depends on whether one or more rows of data collected from the foreign table fit in the communication buffer size specified by the pd_sql_send_buff_size operand. If the data fits, HiRDB efficiently processes the data collected from the foreign table. If the data does not fit. HiRDB suppresses the memory used for accessing the foreign table.