paul-rogers commented on a change in pull request #1953: Add docs for Drill
Metastore
URL: https://github.com/apache/drill/pull/1953#discussion_r366680924
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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.
Review comment:
(What is the difference between `COLUMNS NONE` and no `COLUMNS` clause at
all?
Might it be worth while having an `EXCLUDE` clause? If I have 12 columns,
but I don't need the `$type` and `$recordNo` columns, it is easier to list the
columns to exclude than to list all columns except these. This is especially
true because the big benefit seems to be that Drill will infer the columns; I
have to list them (but not the types), it seems we have a funny worst of both
worlds situation.)
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