vvysotskyi commented on a change in pull request #1953: Add docs for Drill
Metastore
URL: https://github.com/apache/drill/pull/1953#discussion_r373530287
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File path:
_docs/performance-tuning/drill-metastore/010-using-drill-metastore.md
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+---
+title: "Using Drill Metastore"
+parent: "Drill Metastore"
+date: 2020-01-30
+---
+
+Drill 1.17 introduces the Drill Metastore which stores the table schema and
table statistics. Statistics allow Drill to better create optimal query plans.
+
+The Metastore is an Beta feature; it is subject to change. We encourage you to
try it and provide feedback.
+Because the Metastore is in Beta, the SQL commands and Metastore formats may
change in the next release.
+{% include startnote.html %}In Drill 1.17, this feature is supported for
Parquet tables only and is disabled by default.{% include endnote.html %}
+
+## Enabling Drill Metastore
+
+To use the Drill Metastore, you must enable it at the session or system level
with one of the following commands:
+
+ SET `metastore.enabled` = true;
+ ALTER SYSTEM SET `metastore.enabled` = true;
+
+Alternatively, you can enable the option in the Drill Web UI at
`http://<drill-hostname-or-ip-address>:8047/options`.
+
+## Computing and storing table metadata to Drill Metastore
+
+Once you enable the Metastore, the next step is to populate it with data.
Drill can query a table whether that table
+ has a Metastore entry or not. (If you are familiar with Hive, then you know
that Hive requires that all tables have
+ Hive Metastore entries before you can query them.) In Drill, only add data to
the Metastore when doing so improves
+ query performance. In general, large tables benefit from statistics more than
small tables do.
+
+Unlike Hive, Drill does not require you to declare a schema. Instead, Drill
infers the schema by scanning your table
+ and computes some metadata like MIN / MAX column values and NULLS COUNT
designated as "metadata" to be able to
+ produce more optimizations like filter push-down, etc. If
`planner.statistics.use` option is enabled, this command
+ will also calculate and store table statistics into Drill Metastore.
+
+Unlike Hive, Drill does not require you to declare a schema. Instead, Drill
infers the schema by scanning your table
+ in the same way as it is done during regular select.
+
+## Configuration
+
+Default Metastore configuration is defined in `drill-metastore-default.conf`
file.
+It can be overridden in `drill-metastore-override.conf`. Distribution
configuration can be
+indicated in `drill-metastore-distrib.conf`.
+
+All configuration properties should reside in `drill.metastore` namespace.
+Metastore implementation based on class implementation config property
`drill.metastore.implementation.class`.
Review comment:
Thanks, provided the example with a default value and noted about that and
the possibility of using custom implementation as you have suggested.
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