paul-rogers commented on a change in pull request #2060: DRILL-7706: Implement
Drill RDBMS Metastore for Tables component
URL: https://github.com/apache/drill/pull/2060#discussion_r410827641
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File path: metastore/rdbms-metastore/README.md
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+# RDBMS Metastore
+
+RDBMS Metastore implementation allows to store Drill Metastore metadata in
configured RDBMS.
+
+## Configuration
+
+Currently, RDBMS Metastore is not default Drill Metastore implementation.
+To enable RDBMS Metastore create `drill-metastore-override.conf` and indicate
RDBMS Metastore class:
+
+```
+drill.metastore: {
+ implementation.class: "org.apache.drill.metastore.rdbms.RdbmsMetastore"
+}
+```
+
+### Connection properties
+
+Data source connection properties allows to indicate how to connect to Drill
Metastore database.
+
+`drill.metastore.rdbms.data_source.driver` - driver class name. Required.
+Note, driver must be included into Drill classpath prior to start up for all
databases except of SQLite.
+
+`drill.metastore.rdbms.data_source.url` - connection url. Required.
+
+`drill.metastore.rdbms.data_source.username` - database user on whose behalf
the connection is
+being made. Optional, if database does not require user to connect.
+
+`drill.metastore.rdbms.data_source.password` - database user's password.
+Optional, if database does not require user's password to connect.
+
+`drill.metastore.rdbms.data_source.properties` - specifies properties which
will be used
+during data source creation. See list of available [Hikari
properties](https://github.com/brettwooldridge/HikariCP)
+for more details.
+
+### Default configuration
+
+Out of the box, Drill RDBMS Metastore is configured to use embedded file
system based SQLite database.
+It will be created locally in user's home directory under
`${drill.exec.zk.root}"/metastore` location.
+
+Default setup can be used only in Drill embedded mode.
+If SQLite setup will be used in distributed mode, each drillbit will have it's
own SQLite instance
+which will lead to bogus results during queries execution.
+In distributed mode, database instance must be accessible for all drillbits.
+
+### Custom configuration
+
+`drill-metastore-override.conf` is used to customize connection details to the
Drill Metastore database.
+See `drill-metastore-override-example.conf` for more details.
+
+#### Example of PostgreSQL configuration
+
+```
+drill.metastore: {
+ implementation.class: "org.apache.drill.metastore.rdbms.RdbmsMetastore",
+ rdbms: {
+ data_source: {
+ driver: "org.postgresql.Driver",
+ url:
"jdbc:postgresql://localhost:1234/mydb?currentSchema=drill_metastore",
+ username: "user",
+ password: "password"
+ }
+ }
+}
+```
+
+Note: PostgreSQL JDBC driver must be present in Drill classpath.
+
+#### Example of MySQL configuration
+
+```
+drill.metastore: {
+ implementation.class: "org.apache.drill.metastore.rdbms.RdbmsMetastore",
+ rdbms: {
+ data_source: {
+ driver: "com.mysql.cj.jdbc.Driver",
+ url: "jdbc:mysql://localhost:1234/drill_metastore",
+ username: "user",
+ password: "password"
+ }
+ }
+}
+```
+
+Note: MySQL JDBC driver must be present in Drill classpath.
+
+##### Driver version
+
+For MySQL connector version 6+, use `com.mysql.cj.jdbc.Driver` driver class,
+for older versions use `com.mysql.jdbc.Driver`.
+
+## Tables structure
+
+Drill Metastore consists of components. Currently, only `tables` component is
implemented.
+This component provides metadata about Drill tables, including their segments,
files, row groups and partitions.
+In Drill `tables` component unit is represented by `TableMetadataUnit` class
which is applicable to any metadata type.
+Fields which are not applicable to particular metadata type, remain unset.
+
+In RDBMS Drill Metastore each `tables` component metadata type has it's own
table.
+There are five tables: `TABLES`, `SEGMENTS`, `FILES`, `ROW_GROUPS`,
`PARTITIONS`.
+These tables structure and primary keys are defined based on fields specific
for each metadata type.
+See `src/main/resources/db/changelog/changes/initial_ddls.yaml` for more
details.
+
+### Tables creation
+
+RDBMS Metastore is using
[Liquibase](https://www.liquibase.org/documentation/core-concepts/index.html)
+to create all needed tables during RDBMS Metastore initialization, users
should not create any tables manually.
+
+### Database schema
+
+Liquibase is using yaml configuration file to apply changes into database
schema: `src/main/resources/db/changelog/chnagelog.yaml`.
+It converts yaml content into DDL / DML commands suitable to database syntax
based on connection details.
+See list of supported databases: https://www.liquibase.org/databases.html.
+
+All Drill Metastore tables will be created in database default schema, unless
schema is set in the connection url.
+It's recommended prior to using RDBMS Metastore to create dedicated Drill
Metastore schema, for example, `drill_metastore`
+and indicate it in the connection url.
Review comment:
The Drill Metastore tables are created in the database schema indicated in
the connection URL. This will be the default schema unless you specify a
different schema. Drill will not create the schema, however. Best practice is
to create a schema within your database for the Drill metastore before
initializing the metastore.
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