paul-rogers commented on a change in pull request #1953: Add docs for Drill
Metastore
URL: https://github.com/apache/drill/pull/1953#discussion_r366683160
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File path:
_docs/sql-reference/sql-commands/007-analyze-table-refresh-metadata.md
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@@ -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.
Review comment:
(Please explain what `planner.enable_statistics` means.)
You cannot use this command if statistics is disabled. Statistics usage is
enabled by setting the SYSTEM/SESSION option `planner.enable_statistics`. It is
(what?) by default. To enable statistics:
```
ALTER SYSTEM SET `planner.enable_statistics` = true
```
(Note: This behavior seems odd. Why can't I first gather stats and review
them for quality before I have my users start using them? As it is, there is no
ability to gather them, enable the option for a session for testing, verify
that things work right, then turn it on for everyone.
Also, what happens if I turn the option on, gather stats, then turn the
option off? If we refuse to gather stats, do we automatically delete them if
the option is disabled?)
if statistics usage is disabled, the command
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