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

Metadata Tables
HP NonStop SQL/MX Reference Manual—540440-003
10-44
Histograms
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 volumes used tor UPDATE
STATISTICS temporary files, specified as ‘$volume’
with the volume name or names enclosed in single
quotes.You may specify multiple locations separated by
commas. Every volume specified in the list must be
unique.
NonStop SQL/MX will calculate how many partitions are
needed based on the sample set retrieved by the
SAMPLE option. If NonStop SQL/MX determines that it
needs more disks than you specified in that option, it will
use all the disks you list for this attribute.
You may create as many partitions as there are CPUs on
the local node.
You should distribute the partitions evenly across the
CPUs on the local node. That is, specify volumes so that
the first volume in the list is controlled by CPU0, the
second volume is controlled by CPU1, the third volume is
controlled by CPU2, the fourth volume is controlled by
CPU3, and so on.
Only SQL/MX temporary tables may be hash partitioned.
If you specify more than one volume for a SQL/MP
temporary table, only the first volume will be used.
The default is a blank. 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.
Attribute Setting