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DBAL Transport Options and Limitations


    default: 'dbal'
      connection: default                  # doctrine dbal connection name
      table: oro_message_queue             # table name where messages will be stored
      pid_file_dir: /tmp/oro-message-queue # RedeliverOrphanMessagesExtension stores consumer pid files here
      consumer_process_pattern: ':consume' # used by RedeliverOrphanMessagesExtension to check the working or non-working consumers
                                           # (see limitations section for more details)
      polling_interval: 1000               # consumer polling interval in milliseconds
                                           # (see limitations section for more details)


As RDBMS are not designed to work as message queue implementation has several limitations.

  • There is no way to use event-driven model and listen for new inserts into DB. We use polling model to ask DB it has new messages. We run such queries ones per second by default and it means every consumer receives only one message per second. Use polling_interval option to change this value but low interval values may cause DB load
  • When consumer receives message it updates DB record with unique identifier so any other consumer cant receive this message. After job is done and message is acknowledged consumer removes this record from the DB. This is a success story but sometimes error happens and is possible when we got fatal error consumer process is dead now but “locked” message are still in the DB. For such cases there is RedeliverOrphanMessagesExtension which time to time searches for messages which are consumed but not acknowledged and redelivers these messages.
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