Apache ActiveMQ -- KahaDB

KahaDB like the AMQ Message Store is a file based persistence database that is local the message broker that is using it. It makes some trade-offs for scalability and recovery versus performance compared to the AMQ Message Store. Although marginally slower, it is not limited by the number of file descriptors available to the message broker process and also recovery is extremely fast.

Configuration

You can configure ActiveMQ to use KahaDB for its persistence adapter - like below :


 <broker brokerName="broker" persistent="true" useShutdownHook="false">
    <persistenceAdapter>
      <kahaDB directory="activemq-data" journalMaxFileLength="32mb"/>
    </persistenceAdapter>
    <transportConnectors>
      <transportConnector uri="tcp://localhost:61616"/>
    </transportConnectors>
  </broker>

KahaDB Properties

property name	default value	Comments
directory	activemq-data	the path to the directory to use to store the message store data and log files
indexWriteBatchSize	1000	number of indexes written in a batch
indexCacheSize	100	number of index pages cached in memory
enableIndexWriteAsync	false	if set, will asynchronously write indexes
journalMaxFileLength	32mb	a hint to set the maximum size of the message data logs
enableJournalDiskSyncs	true	ensure every non transactional journal write is followed by a disk sync (JMS durability requirement)
maxCheckpointMessageAddSize	4kb	the maximum number of messages to keep in a transaction before automatically committing
cleanupInterval	30000	time (ms) before checking for a discarding/moving message data logs that are no longer used
checkpointInterval	5000	time (ms) before checkpointing the journal

Slow KahaDB access log messages

If database operation is slower than some threshold (default 500 ms), you will see messages like

Slow KahaDB access: cleanup took 1277 | org.apache.activemq.store.kahadb.MessageDatabase | ActiveMQ Journal Checkpoint Worker

You can configure a threshold used to log the message by using

-Dorg.apache.activemq.store.kahadb.LOG_SLOW_ACCESS_TIME=1500

system property and adjust it to your disk speed.

Configuration

KahaDB Properties

Slow KahaDB access log messages

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