Synapse 1.35.0 released

Synapse 1.35.0 is out! This release focused on improving internals as we drive toward better memory performance during room joins, but more on that below.

Update: Synapse 1.35.1 was published on Thursday, June 3rd. It resolves a bug (#10109) which mistakenly listed invite-only rooms in the Spaces summary.

We'd also like to call the attention of client developers to a deprecation: The unstable prefixes used during development of MSC2858: Multiple SSO Identity Providers will be removed from Synapse 1.38, due out in August. Please ensure your client supports the stable identifiers for this feature.

🔗Spaces: On by Default

Following the successful release of Synapse 1.34, the experimental Spaces flag is now enabled by default. If you had manually enabled the experimental_features: { spaces_enabled: true } flag in your homeserver configuration, you may now remove it.

🔗Bug Squashing

This release of Synapse fixes an issue which could cause federated room joins to fail when the join response exceeded a size limit which was too low (#10082). We've also improved what Synapse logs when it drops a connection in similar circumstances (#10091), which should aid diagnosis if a similar issue were to arise in the future.

GitHub user thermaq contributed a fix (#10014) for a bug which could cause user presence state to become stale.

Lastly our OpenTracing support now allows for profiling end-to-end performance on a per-user basis (#9978).

🔗An Update on Room Joins

We've been hammering away at shrinking Synapse's memory footprint when joining large / complex rooms, and while we're not there yet, the end is in sight! In particular, this release includes many internal refactorings, including using ijson to parse the JSON response to /send_join (#9958), clearing the way for substantial improvements.

Memory usage still spikes because we're effectively doing the same work with a different library, but ijson's design allows for iterative parsing. This will pay dividends once we modify the code downstream of /send_join to take advantage of it.

Concretely, Erik Johnston has an experimental branch of Synapse which completely eliminates the memory spike:

The remaining work is centered on splitting that branch into self-contained, reviewable pull requests, like a rewrite of the Synapse Keyring class (#10035). After that's merged, we'll need to make one further change to properly batch up work, at which point we should attain the efficiency gains from Erik's experiment.

🔗Everything Else

GitHub user savyajha contributed a security hardened systemd unit file which effectively sandboxes Synapse (#9803). While not enabled by default, we'd encourage security conscious users to review the example file and associated documentation.

Please see the Release Notes for a complete list of changes in this release.

Synapse is a Free and Open Source Software project, and we'd like to extend our thanks to everyone who contributed to this release, including dklimpel, jerinjtitus, junquera, lonyeon, savyajha, and thermaq.