The following options can help you evaluate the query plan. See the Sybase IQ Reference Manual for details of these options.
NOEXEC When the NOEXEC option is ON, IQ produces a query plan but does not execute the query, except when the EARLY_PREDICATE_EXECUTION option is ON.
QUERY_DETAIL When this option and either QUERY_PLAN or QUERY_PLAN_AS_HTML are both ON, Sybase IQ displays additional information about the query when producing its query plan. When QUERY_PLAN and QUERY_PLAN_AS_HTML are OFF, this option is ignored.
QUERY_PLAN When this option is set ON (the default), Sybase IQ produces messages about queries. These include messages about using join indexes, about the join order, and about join algorithms for the queries.
QUERY_PLAN_AFTER_RUN When you set this option ON, the query plan is printed after the query has finished running. This allows the plan to include additional information, such as the actual number of rows passed on from each node of the query. In order for this option to work, QUERY_PLAN must be ON. This option is OFF by default.
QUERY_PLAN_AS_HTML This option produces a graphical query plan in HTML format for viewing in a Web browser. Hyperlinks between nodes make the HTML format much easier to use than the text format in the .iqmsg file. Use the QUERY_NAME option to include the query name in the file name for the query plan. This option is OFF by default.
QUERY_PLAN_AS_HTML_DIRECTORY When QUERY_PLAN_AS_HTML is turned ON and a directory is specified with QUERY_PLAN_AS_HTML_DIRECTORY, Sybase IQ writes the HTML query plans in the specified directory.
QUERY_TIMING This option controls the collection of timing statistics on subqueries and some other repetitive functions in the query engine. Normally it should be OFF (the default) because for very short correlated subqueries the cost of timing every subquery execution can be very expensive in terms of performance.
Query plans can add a lot of text to your .iqmsg file.
When QUERY_PLAN is ON, and especially
if QUERY_DETAIL is ON, you will probably
want to enable message log wrapping by setting IQMSG_LENGTH_MB to
a positive value.
