- Allow Teradata Database to determine the appropriate threshold
- Specify a change percentage following the THRESHOLD keyword and/or the number of days
You can issue COLLECT STATISTICS requests at regular intervals without being concerned that you might be wasting I/O and CPU by collecting statistics too soon. Teradata skips the recollections for the statistics whose thresholds are not met and recollects the statistics for those columns that are over the threshold. For example, if the threshold is 10% data change and you request a recollection, Teradata skips recollection if less than 10% of the data changed since the last collection.
If you specify the THRESHOLD option the first time you collect statistics, Teradata collects the statistics and remembers the THRESHOLD option. When you recollect statistics, Teradata uses the saved threshold to determine whether statistics recollection is needed. To tell Teradata to ignore the THRESHOLD option (without resetting it) the next time it collects statistics, use the FOR CURRENT option after the percent specification.
To allow Teradata Database to determine the appropriate threshold, in the DBS Control utility disable both the DefaultTimeThreshold and DefaultUserChangeThreshold fields and set the SysChangeThresholdOption field to 0, 1, or 2. By default, DefaultTimeThreshold and DefaultUserChangeThreshold are disabled and SysChangeThresholdOption is 0. See Utilities for information on the different options for these fields.
You can query the LastCollectTimeStamp column of the Data Dictionary table DBC.StatsTbl to see whether data is collected or not.
The user-specified change threshold percent is not supported for statistics on views and queries.
For the syntax of the COLLECT STATISTICS statement, see SQL Data Definition Language.