This is mostly dead code and has been for multiple releases - we don't send any log entries with the snapshots any more:
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usesReplicatedTruncatedState, err := storage.MVCCGetProto( |
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ctx, snap.EngineSnap, keys.RaftTruncatedStateLegacyKey(r.RangeID), hlc.Timestamp{}, nil, storage.MVCCGetOptions{}, |
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) |
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if err != nil { |
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return errors.Wrap(err, "loading legacy truncated state") |
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} |
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|
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canAvoidSendingLog := !usesReplicatedTruncatedState && |
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snap.State.TruncatedState.Index < snap.State.RaftAppliedIndex |
Also, as of 21.2 (i.e. master now), we actually know for sure it is dead code:
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// TruncatedAndRangeAppliedStateMigration is part of the migration to stop |
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// using the legacy truncated state within KV. After the migration, we'll be |
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// using the unreplicated truncated state and the RangeAppliedState on all |
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// ranges. Callers that wish to assert on there no longer being any legacy |
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// will be able to do so after PostTruncatedAndRangeAppliedStateMigration is |
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// active. This lets remove any holdover code handling the possibility of |
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// replicated truncated state in 21.2. |
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// |
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// TODO(irfansharif): Do the above in 21.2. |
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TruncatedAndRangeAppliedStateMigration |
This will let us significantly simplify kvBatchSnapshotStrategy.Send, which can always assume that the truncated index for the snapshot matches the applied index because this branch becomes unconditional:
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if canAvoidSendingLog { |
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// If we're not using a legacy (replicated) truncated state, we avoid |
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// sending the (past) Raft log in the snapshot in the first place and |
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// send only those entries that are actually useful to the follower. |
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// This is done by changing the truncated state, which we're allowed |
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// to do since it is not a replicated key (and thus not subject to |
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// matching across replicas). The actual sending happens here: |
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_ = (*kvBatchSnapshotStrategy)(nil).Send |
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// and results in no log entries being sent at all. Note that |
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// Metadata.Index is really the applied index of the replica. |
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snap.State.TruncatedState = &roachpb.RaftTruncatedState{ |
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Index: snap.RaftSnap.Metadata.Index, |
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Term: snap.RaftSnap.Metadata.Term, |
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} |
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} |
The one weird little thing is this line,
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snap.State.TruncatedState.Index < snap.State.RaftAppliedIndex |
and whether it can ever be false. I don't think it can, as truncations only become visible when they are applied (at least that's how we're doing it today). So this can be turned into an errors.AssertionFailedf.