Add timeline offload mechanism #8907
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1665c67 at 2024-10-07T23:50:16.674Z :recycle: |
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jcsp
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marking as ready for review as I can add a test in a later PR (it needs additional functionality to manually offload). |
VladLazar
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Persist timeline offloaded state to S3. Right now, as of #8907, at each restart of the pageserver, all offloaded state is lost, so we load the full timeline again. As it starts with an empty local directory, we might potentially download some files again, leading to downloads that are ultimately wasteful. This patch adds support for persisting the offloaded state, allowing us to never load offloaded timelines in the first place. The persistence feature is facilitated via a new file in S3 that is tenant-global, which contains a list of all offloaded timelines. It is updated each time we offload or unoffload a timeline, and otherwise never touched. This choice means that tenants where no offloading is happening will not immediately get a manifest, keeping the change very minimal at the start. We leave generation support for future work. It is important to support generations, as in the worst case, the manifest might be overwritten by an older generation after a timeline has been unoffloaded (and unarchived), so the next pageserver process instantiation might wrongly believe that some timeline is still offloaded even though it should be active. Part of #9386, #8088
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Before, we didn't copy over the `index-part.json` of offloaded timelines to the new shard's location, resulting in the new shard not knowing the timeline even exists. In #9444, we copy over the manifest, but we also need to do this for `index-part.json`. As the operations to do are mostly the same between offloaded and non-offloaded timelines, we can iterate over all of them in the same loop, after the introduction of a `TimelineOrOffloadedArcRef` type to generalize over the two cases. This is analogous to the deletion code added in #8907. The added test also ensures that the sharded archival config endpoint works, something that has not yet been ensured by tests. Part of #8088
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Implements an initial mechanism for offloading of archived timelines.
Offloading is implemented as specified in the RFC.
For now, there is no persistence, so a restart of the pageserver will retrigger downloads until the timeline is offloaded again.
We trigger offloading in the compaction loop because we need the signal for whether compaction is done and everything has been uploaded or not.
Part of #8088