Preserve last-committed data at accept time#92258
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DaveCTurner wants to merge 1 commit intoelastic:mainfrom
Closed
Preserve last-committed data at accept time#92258DaveCTurner wants to merge 1 commit intoelastic:mainfrom
DaveCTurner wants to merge 1 commit intoelastic:mainfrom
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The cluster coordination consistency layer relies on a couple of fields within `Metadata` which record the last _committed_ values on each node. In contrast, the rest of the cluster state can only be changed at _accept_ time. In the past we would copy these fields over from the master on every publication, but since elastic#90101 we don't copy anything at all if the `Metadata` is unchanged on the master. However, the master computes the diff against the last _committed_ state whereas the receiving nodes apply the diff to the last _accepted_ state, and this means if the master sends a no-op `Metadata` diff then the receiving node will revert its last-committed values to the ones included in the state it last accepted. With this commit we adjust `CoordinationState` to ignore changes to the last-committed fields at accept time.
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I'm not convinced this is the right fix. I mean it makes sense on the face of it but it introduces a deviation from this line of the formal model so we need to re-check everything. An alternative fix is to go back to always copying these two fields over on every publication. That would be safer, but it involves changes in areas unrelated to cluster coordination safety so I worry about the risk of future bugs. |
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Just to add that I think this bug is more of a liveness concern than a safety one: it means that an election may incorrectly wait to collect votes from the previous configuration as well as the current one. |
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Closing this in favour of #92259 |
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The cluster coordination consistency layer relies on a couple of fields within
Metadatawhich record the last committed values on each node. In contrast, the rest of the cluster state can only be changed at accept time.In the past we would copy these fields over from the master on every publication, but since #90101 we don't copy anything at all if the
Metadatais unchanged on the master. However, the master computes the diff against the last committed state whereas the receiving nodes apply the diff to the last accepted state, and this means if the master sends a no-opMetadatadiff then the receiving node will revert its last-committed values to the ones included in the state it last accepted.With this commit we adjust
CoordinationStateto ignore changes to the last-committed fields at accept time.