MySQL: Transaction and Deadlock I have table "tbl_data", where have a lot of rows (3 - 5 million).
I have JAVA (*.jar) module from which I INSERT/UPDATE data into this table.
If I start *.jar file (for example, "run.jar") and after INSERT/UPDATE process I start "run.jar" sequentially, there no problems - works OK.
If I start "run.jar" and then start "run_01.jar" (jar file with the similar logic: INSERT/UPDATE into "tbl_data"), I can get error:


  com.mysql.jdbc.exceptions.jdbc4.MySQLTransactionRollbackException:
  Deadlock found when trying to get lock; try restarting transaction


All actions at "run.jar" executes in transaction, like:


  START TRANSACTION; INSERT INTO tbl_data ...;UPDATE tbl_data ...; COMMIT;


So, I need to have ability make INSERT/UPDATE from several sources at the same time without blocking table for modification (Every jar file UPDATES/INSERTS its own rows in "tbl_data" so it is no problem for data in modification data at the same time).
If you are totally sure about the separation status of your data, you can set the global isolation level to READ COMMITTED or even to READ UNCOMMITTED. The first blocks less from the index, which should be enough in your case. The second one arranges for all SELECT statements to be non blocking. This is as low as you can go.

Whatever you choose, you should set the global isolation level back to REPEATABLE READ as soon as you finished inserting your data.

global means that this applies to all connections, which are established. So this change also affects connections beside your jarfiles. If you have the possibility to change the jarfiles, you should set the connection based isolation level with the SESSION keyword instead in both jarfiles.