SQL/MP Query Guide

Analyzing Query Performance
HP NonStop SQL/MP Query Guide—524488-003
6-5
Simple Query Example
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Elapsed time includes the execution time, I/O time, and the time to display the
result.
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Execution time is the amount of processor time used by the executor.
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The number of records accessed and the number of records used
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Records accessed is the number of rows read (including rows that do not
satisfy the selection criteria).
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The rows are counted for each table, underlying table of a protection view, and
temporary table. If you join a table to itself, separate statistics are reported for
each instance of the table. The number of rows accessed in an index is not
reported.
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This number does not indicate the specific number of physical disk reads or
writes, because the system uses disk caching to reduce the number of physical
read and write operations.
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Records used is the number of rows returned to the executor by the disk
process. If the query includes a join operation, the number of rows returned
might be smaller than the actual number of rows retrieved. The row count for a
delete operation depends on the type of delete operation; a cursor delete
returns a different count than a set delete because of differences in the ways
the types of delete operations are performed.
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In Example 6-1 on page 6-4, all rows must be returned to satisfy the query
(SELECT * with no WHERE clause), so the number of rows accessed and
used is the same.
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The number of disk reads. In Example 6-1 on page 6-4, the data is found in the
disk cache, so there is no need to access the disk.
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The message count. Message count is usually equal to the number of blocks
passed from the disk process to the file system. Sometimes an additional message
is necessary to ensure that the last row was processed. In this example, there
were two disk blocks passed, plus one final message.
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The message lock bytes.