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rabbitmq-server/release-notes/3.6.16.md

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RabbitMQ 3.6.16

RabbitMQ 3.6.16 is a maintenance release that primarily includes selected backports from the 3.7.x series. Users of earlier 3.6.x releases are recommended to upgrade to a 3.7.x release, e.g. 3.7.6.

Upgrades and Compatibility

See the Upgrades documentation guide for general documentation on upgrades.

This release nearly exclusively contains backports of bug fixes, optimisations and small enhancements (e.g. safer defaults) from the 3.7.x series. Some of them are potentially breaking but should only affect a very small percentage of users. They are:

  • The max 255 priority cap is now enforced at all levels
  • Default rabbit.channel_max value is now about 2K, a much safer value than 65K used previously
  • Default idle LDAP connection timeout is now 300 seconds instead of infinity

This release has no other known incompatibilities with versions 3.6.7 through 3.6.15. See the upgrade and compatibility sections in the 3.6.7 release notes if upgrading from an earlier release.

3.6.x Series Support Timeline

Please read this note on RabbitMQ 3.6.x series support timeline.

Core Server

Bug Fixes

  • queue leader locator min-masters incorrectly calculated the number of masters.

    GitHub issue: rabbitmq-server#1519

  • Maximum supported number of queue priorities (255) is now enforced.

    GitHub issue: rabbitmq-server#1590

Enhancements

  • On Erlang 20.2.3 or later, more optimal memory allocators will be used. On some workloads that leads to significant reduction in node's RAM consumption. The change is workload-specific, however, on the workloads tested that do introduce a negative effect (more RAM used) the difference was very small (about 1%).

    It is possible to go back to the previous settings, +MBas aoffcbf +MHas aoffcbf +MBlmbcs 5120 +MHlmbcs 5120 +MMmcs 10, by specifying them in the RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS environment variable.

    On Erlang/OTP releases older than 20.2.3 there will be no default changes.

    GitHub issue: rabbitmq/rabbitmq-server#1604, rabbitmq/rabbitmq-server#1612

  • queue.delete operations will now force delete queues that don't have a promotable master.

    GitHub issue: rabbitmq-server#1501

  • ha-promote-on-failure is a new mirrored queue setting that's similar to ha-promote-on-shutdown but for unexpected leader replica termination.

    GitHub issue: rabbitmq-server#1578

  • Lock contention in internal database is now much lower when a node with a lot of exclusive queues shuts down or is otherwise considered to be unavailable by peers. This means fewer CPU cycles spent cleaning up the exclusive queues.

GitHub issue: rabbitmq-server#1570

  • Default max number of channels allowed on a connection (a.k.a. channel_max) has been lowered from 65535 to 2047. The new default is much safer and will reduce the effect application channel leaks have on node resource consumption. This is a potentially breaking change.

    Systems where a lot (at least hundreds) of channels per connection are used should explicitly override channel_max in the config file to a higher suitable value, e.g.:

[
  {rabbit, [
    {channel_max, 4000}
  ]}
].

GitHub issue: rabbitmq-server#1593

Management Plugin

Bug Fixes

  • Eliminated unnecessary encoding conversions that could lead to increased memory consumption.

    GitHub issue: rabbitmq-management#550

  • rabbitmqadmin could run into an exception with certain formatting settings on Python 2.x.

    GitHub issue: rabbitmq-management#568

  • rabbitmqadmin incorrectly encoded spaces in connection name values

    GitHub issue: rabbitmq-management#579

  • HTTP API stats documentation used incorrect field names.

    GitHub issue: rabbitmq-management#561

Enhancements

LDAP Plugin

Bug Fixes

Upgrading

To upgrade a non-clustered RabbitMQ simply install the new version. All configuration and persistent message data are retained. When upgrading using definitions export/import from versions earlier than 3.6.0, see http://rabbitmq.com/passwords.html.

To upgrade a RabbitMQ cluster, follow the instructions in RabbitMQ documentation.

Source code archives

Warning: The source code archive provided by GitHub only contains the source of the broker, not the plugins or the client libraries. Please download the archive named rabbitmq-server-3.6.16.tar.xz.