paul-rogers commented on a change in pull request #1953: Add docs for Drill Metastore URL: https://github.com/apache/drill/pull/1953#discussion_r366684761
########## File path: _docs/sql-reference/sql-commands/007-analyze-table-refresh-metadata.md ########## @@ -0,0 +1,158 @@ +--- +title: "ANALYZE TABLE REFRESH METADATA" +parent: "SQL Commands" +date: 2020-01-13 +--- + +Starting from Drill 1.17, you can store table metadata (including schema and computed statistics) into Drill Metastore. +This metadata will be used when querying a table for more optimal plan creation. + +{% include startnote.html %}In Drill 1.17, this feature is supported for Parquet tables only and is disabled by default.{% include endnote.html %} + +To enable Drill Metastore usage, the following option `metastore.enabled` should be set to `true`, as shown: + + SET `metastore.enabled` = true; + +Alternatively, you can enable the option in the Drill Web UI at `http://<drill-hostname-or-ip-address>:8047/options`. + +## Syntax + +The ANALYZE TABLE REFRESH METADATA statement supports the following syntax: + + ANALYZE TABLE [table_name] [COLUMNS {(col1, col2, ...) | NONE}] + REFRESH METADATA ['level' LEVEL] + [{COMPUTE | ESTIMATE} | STATISTICS [(column1, column2, ...)] + [ SAMPLE number PERCENT ]] + +## Parameters + +*table_name* +The name of the table or directory for which Drill will collect table metadata. If the table does not exist, or the table + is temporary, the command fails and metadata is not collected and stored. + +*COLUMNS (col1, col2, ...)* +Optional names of the column(s) for which Drill will generate and store metadata. the Stored schema will include all table columns. + +*COLUMNS NONE* +Specifies to ignore collecting and storing metadata for all table columns. + +*level* +Optional varchar literal which specifies maximum level depth for collecting metadata. +Possible values: `TABLE`, `SEGMENT`, `PARTITION`, `FILE`, `ROW_GROUP`, `ALL`. Default is `ALL`. + +*COMPUTE* +Generates statistics for the table to be stored into the Metastore. +If statistics usage is disabled (`planner.enable_statistics` is set to `false`), an error will be thrown when this clause is specified. + +*ESTIMATE* +Generates estimated statistics for the table to be stored into the Metastore. Currently is not supported. + +*(column1, column2, ...)* +The name of the column(s) for which Drill will generate statistics. + +*SAMPLE* +Optional. Indicates that compute statistics should run on a subset of the data. + +*number PERCENT* +An integer that specifies the percentage of data on which to compute statistics. For example, if a table has 100 rows, `SAMPLE 50 PERCENT` indicates that statistics should be computed on 50 rows. The optimizer selects the rows at random. + +## Related Options + +- **metastore.enabled** +Enables Drill Metastore usage to be able to store table metadata during ANALYZE TABLE commands execution and to be able + to read table metadata during regular queries execution or when querying some INFORMATION_SCHEMA tables. Default is `false`. +- **metastore.metadata.store.depth_level** +Specifies maximum level depth for collecting metadata. Default is `'ALL'`. +- **metastore.retrieval.retry_attempts** +Specifies the number of attempts for retrying query planning after detecting that query metadata is changed. Review comment: If you run the `ANALYZE TABLE` command at the same time as queries run, then the query can read incorrect or corrupt statistics. Drill will reload statistics and replan the query. This option specifies the maximum number of retry attempts. (Drill is a multi-user system. We should certainly allow concurrent queries and metadata updates!) ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services