![]() There are a few things that can be tried, depending on version. The steps below talk about methods to reduce the amount of data in the database – a query won’t show up as being inefficient until there is lots of data to trawl through, so generally they occur in large databases where this is lots of contention from a high number of resource PCs – before reducing the data it’s worth getting the info from the database so we can improve the product ( the related article on database timeouts describes how this can be done in more detail). These don’t have to be records in a table necessarily – they can be locking indexes for update or select in different orders.ĭeadlocks are usually exacerbated by slow running queries, so first step is to get the worst query plans from the DBA and start to look for big table or index scans or CPU intensive loops and joins. The trace flags described in the resolution below will give us this information. This means the deadlock victim as reported in the error is only one side of the story – to get the full story we need a deadlock graph from the database server, which shows which two transactions were involved and on which objects they were deadlocked. SQL Server normally kills the cheapest query, the one it will have the least effort in rolling back. The only way out is for SQL Server to kill one of the queries. Process Y can’t get record A until Process X releases it, and Process X can’t release it until it gets record B, hence they are deadlocked. Retry the transaction 3 times on failure with an interval of 5 minutes.Deadlocks occur when query X locks records A then B and query Y locks B then A. I also added few minutes sleep before retrying the same transaction e.g. I’d to modify my script to retry the transaction if there is a failure. So to completely solve the problem I followed the suggestion. Galera uses optimistic locking which may results to deadlock retrying the transaction again is most suggested in that scenario. 1/10 times But now it’s a known behavior of Galera. It stopped that deadlock error almost.īut still the same deadlock error was coming at random e.g. I removed id from that query and kept some_identifier_id as the unique key to support the same replace query. Inserting or replacing auto-incremental primary key is the most probable and obvious reason of deadlock in Galera. So it’s quite possible to get deadlock when the replace into query syncing id from db1.table1 to db.table2. Galera Cluster uses at the cluster-level optimistic concurrency control, which can result in transactions that issue a COMMIT aborting at that stage. Galera uses a mechanism based on autoincrement increment to produce unique non-conflicting sequences, so on every single node the sequence will have gaps. Which helped me to realize the actual problem.ĭo not rely on auto-increment values to be sequential. After some research I found some useful articles known limitations of mariadb galera cluster, Differences from a standalone MySQL server etc. So the only way- checkout any of the documents… whatever is available. But none of these actually solved the problem. LOCK IN SHARE MODE, ordering by id or checking the log SHOW ENGINE INNODB STATUS etc. The above points were enough for me to start some research on how Galera works. Let’s assume in production I have 5 DB servers with multi-master synchronous replication using Galera cluster. Executing the query in any of the individual nodes within cluster leads to failure.All the tables are InnoDB db1.table1 => Collation: latin1_swedish_ci and in db2 both of the tables => Collation: utf8_unicode_ci.The query works fine in development server but fails in production server.The source table has approximately 50k records only. | some_other_identifier_id | varchar(255) | YES | | NULL | | | some_identifier_id | varchar(255) | YES | UNI | NULL | | | some_identifier_id | varchar(255) | YES | MUL | NULL | | | updated_at | datetime | YES | | NULL | | | created_at | datetime | YES | | NULL | | | id | int(11) | NO | PRI | NULL | auto_increment | | Field | Type | Null | Key | Default | Extra | REPLACE INTO db2.table2 (id, some_identifier_id, name, created_at, updated_at) (SELECT id, some_identifier_id, name, created_at, updated_at FROM db1.table1 WHERE some_identifier_id IS NOT NULL AND some_identifier_id NOT IN (SELECT some_identifier_id FROM db2.table1 WHERE some_other_identifier_id IS NOT NULL)) ĮRROR 1213 (40001): Deadlock found when trying to get lock try restarting transaction Though the script was successfully running in development server but in production it was continuously failing for a query with deadlock error. There was a requirement to migrate data from one database to another from one schema to another on a daily basis. Recently I was working on a data migration script. ![]()
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