Managed statistics

You can configure Starburst Enterprise platform (SEP) to collect and store its own managed Table statistics for some data sources that only collect or expose a limited number of statistics. These additional statistics can then enable the query planner to make better-informed, cost-based optimizations.

Configuration

Managed statistics requires the following:

• A valid backend service configuration and underlying database.

• An internal shared secret to secure transmission of statistics.

Note

The managed statistics feature is only supported in select connectors. Reference the connectors feature matrix for more information about which connectors support this feature.

Coordinator node configuration

In order to enable managed statistics for a cluster, add the following configuration properties to config.properties on the coordinator node only:

starburst.managed-statistics.enabled=true

Catalog configuration

In addition to enabling managed statistics for the cluster, you must also enable managed statistics for each catalog.

To enable managed statistics for a catalog, add the following catalog configuration property to the catalog configuration file under etc/catalog:

managed-statistics.enabled=true

Managed statistics configuration properties

The following configuration properties are used to control managed statistics on the coordinator:

Managed statistics configuration properties

Property name	Description
starburst.managed-statistics.enabled	Enables managed statistics on a cluster. Defaults to false.
managed-statistics.cache-ttl	Maximum amount of time for managed statistics to be stored on the in-memory cache on the coordinator before they are retrieved from the database. For more information see statistics storage and management. Default value is 10m.
managed-statistics.cache-maximum-size	Maximum number of objects stored in the in-memory statistics cache. If this value is exceeded, the least-used statistics are discarded and only retrieved again from the database when the query planner needs to reference them. Defaults to 1000.

Collecting statistics

Managed statistics must be collected manually with the ANALYZE statement or the collect_statistics command in an ALTER TABLE EXECUTE statement depending on the connector. The optional column parameter is used to limit statistics collection to a specified array of column names. See the connector documentation for more information on ALTER TABLE EXECUTE or ANALYZE statement support and syntax for that connector.

The following statistics are collected:

• For a table:

  • Row count: The total number of rows in the table.

• For each column in a table:

  • Nulls fraction: The fraction of null values.

  • Distinct value count: The number of distinct values.

  • Range: For data types that have a range, the range of values.

  • Data size: For textual data types, the total data size of all values.

Note

Other methods of collecting statistics continue to be used for a table until you execute the collect_statistics command on that table. Collecting statistics for one table using the collect_statistics command does not prevent SEP from continuing to collect statistics for other tables from the catalog.

If you use the collect_statistics command on large tables, specify a subset of important columns instead of collecting statistics for all columns in the table. Statistics collection should target primary keys and columns used in query operations such as filters, joins, and aggregate functions.

Storage and management

When statistics are collected, they are stored in the backend service database indefinitely until collect_statistics is run again and overwrites any stale statistics. These statistics are pulled from the database into an in-memory cache on the coordinator at a frequency defined by the managed-statistics.cache-ttl configuration property which defaults to 10 minutes. The query planner accesses this in-memory cache for statistics instead of the backend service database, reducing network I/O on the database at the cost of additional memory usage on the coordinator node. To disable the in-memory cache and have the query planner directly access the backend service database for statistics, set the managed-statistics.cache-ttl property to 0.

The in-memory cache retrieves its statistics from the SEP database, not from catalogs directly, so you must still routinely run the collect_statistics command to ensure that the cache does not store stale statistics.