To update information about the distribution of key values in specified indexes, for all columns in an index, table, or partition, the syntax is:. Your situation, of course, may be different. Here are a few considerations when choosing which option will work best in your circumstances:. When you increase the steps, it changes the number of histogram points that the optimizer has to work with. When would you do this? If you ever find your performance to be erratic, increasing the number of steps may be a good place to start.
You can examine the statistics including time since the last update by querying the systabstats and sysstatistics table, or by using the optdiag utility from the OS prompt. Some have claimed the update statistics command causes blocking and contention.
In earlier versions of ASE, this may have sometime happened; however, in the newer releases of ASE, locking is minimal and this should not be a significant concern. In general, if you are updating statistics for a table that has allpages locking defined, the server places an intent lock at the table level, and a page lock on the page currently being scanned.
Locking level 1. As noted at the beginning, out-of-date statistics is a frequent cause of poor performance. Assess your circumstances and develop a plan for keeping your statistics up to date, so that the query optimizer can do its job. There is an insert trigger on the table T1. What will happen if we fire the following statement? By default, dropping then recreating an index on a table with data overwrites any statistics on its leading column.
By default creating an index on an empty table generates statistics on its leading column. By default creating an index on a table with data generates statistics on its leading column. Save my name, email, and website in this browser for the next time I comment. Toggle navigation.
Options for updating statistics ASE provides a number of options for updating statistics, depending on the specific needs you have. Which update statistics option is best? Here are a few considerations when choosing which option will work best in your circumstances: You can update statistics for a specific partition. You can update statistics for either a specific index or all of the indexes on a specific table. In general, you would run this on an entire table; for very large tables, you can update statistics on just the columns that skew the most.
You can change the number of histogram steps to create the default is 20 steps. You can configure this at the server level new in late ASE The sampling allows you to reduce the number of rows you have to scan in order to build the histogram. The value for N is any number between 1 and If update index statistics is used with just a table name, it updates statistics for all columns in all indexes of the table.
Specifying the name of an unindexed column or the nonleading column of an index generates statistics for that column without creating an index. Density statistics are created for all the prefix subsets of the columns of index es whose statistics are being updated. If you use update index statistics on a specific partition, you update global statistics implicitly as well. The partition statistics serve as input to global statistics creation and enable per-partition DDL operations.
Global statistics are used by the optimizer. If you run the update index statistics command for a specific data partition, the table statistitics are generated and updated only for that data partition and for any local index partitions. Global indexes are skipped. If you run the update index statistics for a specific index partition, only the table statistics for that index partition are updated. The update index statistics command generates a series of update statistics operations that use the same locking, scanning, and sorting as the equivalent index-level and column-level command.
The command can also be executed by the Database Owner, who can impersonate the table owner by running the setuser command.
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