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DistributedLock.MySql.md

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DistributedLock.MySql

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The DistributedLock.MySql package offers distributed synchronization primitives based on MySQL/MariaDB user locks. For example:

var @lock = new MySqlDistributedLock("mylockname", connectionString);
await using (await @lock.AcquireAsync())
{
   // I have the lock
}

APIs

  • The MySqlDistributedLock class implements the IDistributedLock interface.
  • The MySqlDistributedSynchronizationProvider class implements the IDistributedLockProvider and IDistributedReaderWriterLockProvider interfaces.

Implementation notes

MySQL-based locks have been tested against and work with both the MySQL and MariaDB.

MySQL-based locks locks can be constructed with a connectionString, an IDbConnection or an IDbTransaction as a means of connecting to the database. In most cases, using a connectionString is preferred because it allows for the library to efficiently multiplex connections under the hood and eliminates the risk that the passed-in IDbConnection gets used in a way that disrupts the locking process. Using an IDbTransaction is generally equivalent to using an IDbConnection (the lock is still connection-scoped), but it allows the lock to participate in an ongoing transaction. NOTE that since IDbConnection/IDbTransaction objects are not thread-safe, lock objects constructed with them can only be used by one thread at a time.

Natively, MySQL's locking functions are case-insensitive with respect to the lock name. Since the DistributedLock library as a whole uses case-sensitive names, lock names containing uppercase characters will be transformed/hashed under the hood (as will empty names or names that are too long). If your program needs to coordinate with other code that is using GET_LOCK directly, be sure to express the name in lower case and to pass exactName: true when constructing the lock instance (in exactName mode, an invalid name will throw an exception rather than silently being transformed into a valid one).

Options

In addition to specifying the name, several tuning options are available for connectionString-based locks:

  • KeepaliveCadence allows you to have the implementation periodically issue a cheap query on a connection holding a lock. This helps in configurations which are set up to aggressively kill idle connections. Defaults to OFF (Timeout.InfiniteTimeSpan).
  • UseMultiplexing allows the implementation to re-use connections under the hood to hold multiple locks under certain scenarios, leading to lower resource consumption. This behavior defaults to ON. Note that this behavior must be disabled if you are using a version of MySQL older than 5.7 (see here and here for more). Otherwise, you should not disable it unless you suspect that it is causing issues for you (please file an issue here if so!).