SQL/MX 2.x Reference Manual (H06.04+)

Metadata Tables
HP NonStop SQL/MX Reference Manual—540440-003
10-43
Histograms
HIST_NO_STATS_REFRESH_
INTERVAL
Specifies the time interval, in seconds, at which default
statistics are refreshed. Default statistics are compiler
generated statistics for tables for which no UPDATE
STATISTICS has been performed.
You can change the value of
HIST_NO_STATS_REFRESH_INTERVAL if you do
frequent inserts and deletes on such tables, for example,
a temporary table. If you set this value to 0, default
statistics are never cached, and new default statistics are
generated by the compiler for every statement, based on
the current tables' sizes.
Allowable values: 0 through 4294967040.
The default value is 3600 seconds.
HIST_NO_STATS_ROWCOUNT Estimated row count when current histogram statistics do
not exist for a table. Used with HIST_NO_STATS_UEC.
Adjust these settings when the query execution plan
shows that costing values are incorrect because of a lack
of statistics on a table involved in the query.
Allowable values: 1 through 1.1579208e77.
The default is 100 rows.
HIST_NO_STATS_UEC Estimated unique entry count (UEC) when current
histogram statistics do not exist. Used with
HIST_NO_STATS_ROWCOUNT.
HIST_NO_STATS_UEC must be less than or equal to
HIST_NO_STATS_ROWCOUNT.
Allowable values: 1 through 1.1579208e77.
The default is 100 unique entries.
HIST_PREFETCH Set to ON or OFF. When set to ON, NonStop SQL/MX
determines if histograms are prefetched for caching. The
compiler fetches histograms for all the columns of a table
and places them in the cache to improve optimizer
performance. The CACHE_HISTOGRAMS attribute must
be set to ON for histograms to be prefetched.
If OFF, histograms are cached only for columns of a table
that is involved in a statement.
The default setting is ON.
Attribute Setting