NATS Server 2.9.18 Release

Byron Ruth — June 14, 2023

The NATS maintainers are happy to announce the 2.9.18 release ! We want to thank all of the people who contributed to this release through reporting issues and code contributions! If you are interested in contributing, please check out all the ways you can !

This release was a smaller one than the prior few, but there are still some key areas to cover, including:

For the entirety of the improvements and fixes, check out the release notes .

🗑️ Process purge replay properly on startup

Purge is an on-demand operation that can be applied to a stream to delete a subset of messages in the stream. A purge operation takes a few opt-in options including:

  • sequence to purge all messages up to, but not including the message with the sequence
  • subject to purge all message matching the subject (wildcards supported)
  • keep option indicating the number of newest messages to keep, having all previous messages deleted

If none of these options are set, all messages in the stream will be deleted.

An issue was observed where a purge using one of these options, followed by immediately restarting servers in a cluster could resort to an unintentional full purge of a stream.

The probability of this occurring in practice is fairly low, but given the risk of data loss, it was clearly flagged as high priority and this release introduces the fix to apply the correct purge. That said, if you do not perform on-demand filtered purges, there is no risk of this bug.

Relevant PRs

🔗 Daisy-chained leafnodes losing interest

Leafnodes are leveraged to extend an existing NATS system (cluster/supercluster), providing isolation of NATS traffic bound to explicit accounts and bridging separate operational and security boundaries.

In practice, leafnodes are typically deployed at edge locations or devices where messaging, streaming, etc. can be leveraged by co-located applications. If/when these leafnodes are connected to a hub cluster, data can synchronize in either direction.

For some use cases, there may be a need to daisy-chain leafnodes from other leafnodes rather than directly to the hub. Since each leafnode can be configured with different operational and security boundaries, each daisy-chain layer could apply different policies in terms of account binding or security bridging.

For some daisy-chained setups, there was a regression introduced in 2.9.17 which caused interest propagation of subjects to not fully traverse these layers, resulting in messages not being delivered to all interested subscribers.

Relevant PRs

💨 Optimize KV get for large key spaces and small messages

For those new to the Key-Value capability in NATS, it is a client abstraction on top of a standard stream. There are various stream configurations that are used to ultimately make the stream behave like a key-value store, such as setting the MaxMsgsPerSubject limit to enforce a limit on the number of messages that can be retained per subject. From a key-value standpoint, each subject corresponds to a key and the message data correspond to the key’s value.

It is a common use case to use key-value stores for caches that may have a large number of keys for high cardinality identifiers, such as user_id. Prior to this release, there was a fairly strong degradation of key-value get performance as the number of keys increased. This was particularly noticeable when the value size was small.

An optimization was introduced that essentially skips an unnecessary scan operation for this workload that literally 10x’ed the operations per second. See the before and after comparison if you are curious!

Relevant PRs

😰 Remediate potential panic scenarios

The NATS community is fantastic and every so often we get contributions from folks who are merely perusing the source code and observing improvements that can be made. This contribution was just that.

A couple of folks from InfoWatch observed a few areas in the code where panic scenarios could arise and remediated them, putting in place guards where appropriate.

Relevant PRs


Among the handful of other fixes and improvements, if any of these affect you, please update your NATS system and provide us feedback! Thanks again to all the contributors of this release.

As always, refer to the download page for direct links to the GitHub release page and the official Docker image.

If you prefer to track nightly builds on the main branch, which follows the stable series (currently 2.9.x), images are available on Docker hub: synadia/nats-server:nightly-main .

About the Author

Byron Ruth is the Director of Developer Relations at Synadia and a long-time NATS user.

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