Apache Accumulo 1.9.1

14 May 2018

Apache Accumulo 1.9.1 contains bug fixes for a critical data loss bug. Users of 1.8.0, 1.8.1, or 1.9.0 are encouraged to upgrade immediately.

  • User Manual - In-depth developer and administrator documentation
  • Javadocs - Accumulo 1.9 API
  • Examples - Code with corresponding readme files that give step by step instructions for running example code

Notable Changes

Fixes for Critical WAL Data Loss Bugs (affects versions 1.8.0-1.9.0)

Accumulo 1.9.1 contains multiple bug fixes for write ahead log recovery. Write ahead log recovery is the process of restoring data that was in memory when a tablet server died. These bugs could lead to data loss and are present in 1.8.0, 1.8.1, and 1.9.0. Because the bugs can negatively impact Accumulo’s metadata table, even users that mainly use bulk import may be affected. It is strongly recommended that anyone using 1.8.0 or greater upgrade immediately. For more information see issues #441 and #449. These issues were fixed in pull request #443 and #458.

The only users who would not be affected by these bugs would be users already running Accumulo without the recommended write-ahead logs enabled at all (durability: none), including for the metadata tables. Such users are already risking data loss when a server fails, but are not subject to any additional risk from these bugs, which occur during automated recovery from such failures.

Some WAL recovery files were not being properly cleaned up

A less serious bug than the above critical bugs was discovered and fixed, pertaining to write-ahead log recovery. This bug involved recovery files not being removed properly when no longer required and was fixed in #432.

Other Changes

  • GitHub - List of issues tracked on GitHub corresponding to this release
  • 1.9.0 release notes - Release notes showing changes in the previous release, 1.9.0


View the Upgrading Accumulo documentation for guidance.


Continuous ingest with agitation and all integration test were run against this version. Continuous ingest was run with 9 nodes for 24 hours followed by a successful verification. The integration tests were run against both Hadoop 2.6.4 and Hadoop 3.0.0.

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