SQL/MX 2.x Reference Manual (G06.24+, H06.03+)

Metadata Tables
HP NonStop SQL/MX Reference Manual—523725-004
10-43
Histograms
For more information about histogram statistics, see the SQL/MX Query Guide.
HIST_ROWCOUNT_
REQUIRING_STATS
Row count that determines when SQLCODE 6007/6008
warnings are issued, which mean statistics have not
been updated for all table columns in a query. Only
columns from tables that have more rows than this count
force these warnings. To avoid these warnings, set this
value to a very large number, provided no tables exist
with that number of rows in the database.
If a file is fragmented, NonStop SQL/MX cannot estimate
an accurate row count, and you can receive warning
6008 even if you have set this value to a very large
number. You should execute UPDATE STATISTICS to
make its histogram information current.
The default is 50000 rows. Allowable values: 0 to
4294966784.
HIST_SAME_TABLE_PRED_
REDUCTION
Controls the amount of overlap in predicate selectivity.
Set to a value between 0 (no overlap) and 1 (complete
overlap). Affects plans that have multiple predicates on
the same table, where multicolumn statistics are not
available for the columns in the predicates.
The default is 0.0. Allowable values: 0 to 1.
HIST_SCRATCH_VOL Sets the physical volume used tor UPDATE STATISTICS
temporary files, of the form $volume.
If you do not set this value,NonStop SQL/MX uses the
default volume specified by the _DEFAULTS define for
SQL/MX tables, and the volume of the table’s primary
partition for SQL/MP tables.
HIST_SECURITY_WARNINGS Controls whether MXCMP displays a warning if the user
does not have access permissions to statistics tables and
the user table's estimated rowcount is greater than the
HIST_ROWCOUNT_REQUIRING_STATS value.
If set to ON, the compiler reports this warning.
If set to OFF, the compiler does not report a warning.
The default is ON.
Attribute Setting