There's been a variety of performance improvements to the TSDB. Compaction will now be faster, there will only be one checkpoint made after Prometheus restarts after not running for a good while, and the series API no longer loads any chunks.
Remote write can now send metadata. This is a limited stopgap, only enough to implement the metrics metadata API as there's no way to link a specific sample to its metadata. There have also been a myriad of changes to the remote write metrics exposed by Prometheus itself on /metrics.
The default UI is now the react UI. The old UI is still available for now.
There’s also a number of improvements, bug fixes and other changes, see the release notes for more detail.
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