eG Monitoring
 

Measures reported by MySQLCluDdLkTest

A deadlock is a situation where different transactions are unable to proceed because each holds a lock that the other needs. Because both transactions are waiting for a resource to become available, neither ever release the locks it holds. A deadlock can occur when transactions lock rows in multiple tables (through statements such as UPDATE or SELECT ... FOR UPDATE), but in the opposite order. A deadlock can also occur when such statements lock ranges of index records and gaps, with each transaction acquiring some locks but not others due to a timing issue. When deadlock detection is enabled (the default) and a deadlock does occur, InnoDB (the default MySQL Storage engine) detects the condition and rolls back one of the transactions.

If deadlock detection is disabled, InnoDB relies on the innodb_lock_wait_timeout setting to roll back transactions in case of a deadlock. Though the transactions can be rolled back after the time specified against the innodb_lock_wait_timeout setting, administrators have to patiently wait for the roll back to happen. To avoid such wait time, administrators need to constantly keep a vigil on whether the deadlock detection is enabled or not. The MySQLCluDdLkTest helps administrators in this regard!

This test reports whether/not the deadlock detection is enabled and reports the count of deadlocks that occurred on the target MySQL cluster.

Outputs of the test: One set of results for the cluster being monitored.

The measures made by this test are as follows:

Measurement Description Measurement Unit Interpretation
Is_deadlock_enabled Indicates whether/not deadlock detection is enabled on the database instance.   The values reported by this measure and its numeric equivalents are mentioned in the table below:

Measure Value Numeric Value
Yes 1
No 0
Note:

By default, this measure reports the Measure Values listed in the table above to indicate whether/not deadlock detection is enabled on this instance. The graph of this measure however, is represented using the numeric equivalents only i.e., 0 or 1.
Deadlock_count Indicates the number of deadlocks found in the target database instance. Number A deadlock may arise due to various situations including bad design of queries and deficient coding practices. A deadlock is a situation where both/all the lock requestors are in a mutual or a multi-way tie. Any deadlocks are detrimental to database application performance.

The detailed diagnosis of this measure lists the Deadlock time, Waiting transaction ID, Waiting lock mode, Waiting SQL text, Blocking transaction ID, Blocking lock mode, Blocking SQL text and Rollback transactionID.