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Multiple Connections from a Single Application

Multiple Connections from a Single Application

A single application can work with multiple Connections to the same database and assign them to different threads. The application programmer can avoid concurrency and deadlock problems in several ways:

  • Use the TRANSACTION_READ_COMMITTED isolation level and turn on row-level locking (the defaults).
  • Beware of deadlocks caused by using more than one Connection in a single thread (the most obvious case). For example, if the thread tries to update the same table from two different Connections, a deadlock can occur.
  • Assign Connections to threads that handle discrete tasks. For example, do not have two threads update the Hotels table. Have one thread update the Hotels table and a different one update the Groups table.
  • If threads access the same tables, commit transactions often.
  • Multi-threaded Java applications have the ability to self-deadlock without even accessing a database, so beware of that too.
  • Use nested connections to share the same lock space.

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