Liquibase Extension: Session Lock Support

Provides session-level (vs. transaction-level) LockService implementations. Session-level locks get automatically released if the database connection drops, and overcome the shortcoming of the StandardLockService:

If Liquibase does not exit cleanly, the lock row may be left as locked. You can clear out the current lock by running liquibase releaseLocks which runs UPDATE DATABASECHANGELOGLOCK SET LOCKED=0.

Running liquibase releaseLocks in a micro-service production environment may not be really feasible.

Supported Databases

MySQL
MariaDB
PostgreSQL
Oracle

Support for other databases may be conveniently added by extending SessionLockService.

MySQL / MariaDB

The MySQL and MariaDB implementation rely on user locks: get_lock and is_used_lock are builtin functions for MySQL and MariaDB. The lock is automatically released when the connection is dropped unexpectedly.

PostgreSQL

The Postgres implementation used pg_try_advisory_lock and pg_try_advisory_unlock

Oracle

The Oracle implementation relies on DBMS_LOCK. The user that executes liquibase must have EXECUTE privilege on DBMS_LOCK.

grant execute on SYS.DBMS_LOCK to <user>;

To read lock information, the user needs permissions to read from GV$LOCK and GV$SESSION.

grant select on SYS.GV_$LOCK to <user>;
grant select on SYS.GV_$SESSION to <user>;

MSSQL

The MSSQL implementation used application resources locks with sp_getapplock and sp_releaseapplock

Usage

To use the new lockservice, simply add a dependency to the library. In Liquibase v4.x, because the priority is higher than the StandardLockService, it will automatically be used (provided the database is supported).

In Liquibase v3.7.x and above, especially when used standalone or integrated with Dropwizard framework, com.github.blagerweij.sessionlock string needs to be added to Liquibase classpath scanner's whitelist of packages to scan, by either system property liquibase.scan.packages or Liquibase-Package entry in MANIFEST.mf, as described here . Please note that unit tests are performed for a few versions of Liquibase, starting from v3.5, but other versions might work as well.

Maven

<dependency>
    <groupId>com.github.blagerweij</groupId>
    <artifactId>liquibase-sessionlock</artifactId>
    <version>1.6.0</version>
</dependency>

Gradle

implementation 'com.github.blagerweij:liquibase-sessionlock:1.6.0'

Disclaimer

This module, both source code and documentation, is in the Public Domain, and comes with NO WARRANTY.

License

This module is using the Apache Software License, version 2.0. See http://www.apache.org/licenses/LICENSE-2.0.txt

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