Use index for peer recovery instead of translog #45136
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This creates a peer-recovery retention lease for every shard during recovery, ensuring that the replication group retains history for future peer recoveries. It also ensures that leases for active shard copies do not expire, and leases for inactive shard copies expire immediately if the shard is fully-allocated. Relates elastic#41536
This commit adjusts the behaviour of the retention lease sync to first renew any peer-recovery retention leases where either: - the corresponding shard's global checkpoint has advanced, or - the lease is older than half of its expiry time Relates elastic#41536
If the primary performs a file-based recovery to a node that has (or recently had) a copy of the shard then it is possible that the persisted global checkpoint of the new copy is behind that of the old copy since file-based recoveries are somewhat destructive operations. Today we leave that node's PRRL in place during the recovery with the expectation that it can be used by the new copy. However this isn't the case if the new copy needs more history to be retained, because retention leases may only advance and never retreat. This commit addresses this by removing any existing PRRL during a file-based recovery: since we are performing a file-based recovery we have already determined that there isn't enough history for an ops-based recovery, so there is little point in keeping the old lease in place. Caught by [a failure of `RecoveryWhileUnderLoadIT.testRecoverWhileRelocating`](https://scans.gradle.com/s/wxccfrtfgjj3g/console-log?task=:server:integTest#L14) Relates elastic#41536
This commit updates the version in which PRRLs are expected to exist to 7.4.0.
Today we perform `TransportReplicationAction` derivatives during recovery, and these actions call their response handlers on the transport thread. This change moves the continued execution of the recovery back onto the generic threadpool.
Today when renewing PRRLs we assert that any invalid "backwards" renewals must be because we are recovering the shard. In fact it's also possible to have `checkpointState.globalCheckpoint == SequenceNumbers.UNASSIGNED_SEQ_NO` on a tracked shard copy if the primary was just promoted and hasn't received checkpoints from all of its peers too. This commit weakens the assertion to match. Caught by a [failure of the full cluster restart tests](https://scans.gradle.com/s/5lllzgqtuegty/console-log#L8605) Relates elastic#41536
In elastic#44000 we introduced some calls to `assertNotTransportThread` that are executed whether assertions are enabled or not. Although they have no effect if assertions are disabled, we should have done it like this instead.
Today peer recovery retention leases (PRRLs) are created when starting a replication group from scratch and during peer recovery. However, if the replication group was migrated from nodes running a version which does not create PRRLs (e.g. 7.3 and earlier) then it's possible that the primary was relocated or promoted without first establishing all the expected leases. It's not possible to establish these leases before or during primary activation, so we must create them as soon as possible afterwards. This gives weaker guarantees about history retention, since there's a possibility that history will be discarded before it can be used. In practice such situations are expected to occur only rarely. This commit adds the machinery to create missing leases after primary activation, and strengthens the assertions about the existence of such leases in order to ensure that once all the leases do exist we never again enter a state where there's a missing lease. Relates elastic#41536
The cluster in the full-cluster restart test only has 2 nodes, so we cannot fully allocate an index with 2 replicas.
Today PRRLs are not supported on closed indices or indices where soft deletes are disabled, but (confusingly) nor are they actively forbidden. This commit avoids creating them unnecessarily in unsupported situations.
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Aug 12, 2019
Now that elastic#45136 means we perform recoveries from the index rather than the translog (if soft deletes are enabled) there is no need to retain extra translog for performing peer recoveries. This commit reduces the default translog retention to zero so that it can be discarded more quickly.
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Aug 21, 2019
Since #45136, we use soft-deletes instead of translog in peer recovery. There's no need to retain extra translog to increase a chance of operation-based recoveries. This commit ignores the translog retention policy if soft-deletes is enabled so we can discard translog more quickly. Co-authored-by: David Turner <david.turner@elastic.co> Relates #45136
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Since elastic#45136, we use soft-deletes instead of translog in peer recovery. There's no need to retain extra translog to increase a chance of operation-based recoveries. This commit ignores the translog retention policy if soft-deletes is enabled so we can discard translog more quickly. Co-authored-by: David Turner <david.turner@elastic.co> Relates elastic#45136
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Aug 22, 2019
Since #45136, we use soft-deletes instead of translog in peer recovery. There's no need to retain extra translog to increase a chance of operation-based recoveries. This commit ignores the translog retention policy if soft-deletes is enabled so we can discard translog more quickly. Backport of #45473 Relates #45136
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Nov 21, 2019
Today we do not use retention leases in peer recovery for closed indices because we can't sync retention leases on closed indices. This change allows that ability and adjusts peer recovery to use retention leases for all indices with soft-deletes enabled. Relates #45136 Co-authored-by: David Turner <david.turner@elastic.co>
jimczi
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Nov 22, 2019
Today we do not use retention leases in peer recovery for closed indices because we can't sync retention leases on closed indices. This change allows that ability and adjusts peer recovery to use retention leases for all indices with soft-deletes enabled. Relates elastic#45136 Co-authored-by: David Turner <david.turner@elastic.co>
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Nov 24, 2019
Today we do not use retention leases in peer recovery for closed indices because we can't sync retention leases on closed indices. This change allows that ability and adjusts peer recovery to use retention leases for all indices with soft-deletes enabled. Relates elastic#45136 Co-authored-by: David Turner <david.turner@elastic.co>
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Dec 13, 2019
Since 7.4, we switch from translog to Lucene as the source of history for peer recoveries. However, we reduce the likelihood of operation-based recoveries when performing a full cluster restart from pre-7.4 because existing copies do not have PPRL. To remedy this issue, we fallback using translog in peer recoveries if the recovering replica does not have a peer recovery retention lease, and the replication group hasn't fully migrated to PRRL. Relates #45136
dnhatn
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Dec 15, 2019
Today we do not use retention leases in peer recovery for closed indices because we can't sync retention leases on closed indices. This change allows that ability and adjusts peer recovery to use retention leases for all indices with soft-deletes enabled. Relates elastic#45136 Co-authored-by: David Turner <david.turner@elastic.co>
dnhatn
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Dec 15, 2019
Since 7.4, we switch from translog to Lucene as the source of history for peer recoveries. However, we reduce the likelihood of operation-based recoveries when performing a full cluster restart from pre-7.4 because existing copies do not have PPRL. To remedy this issue, we fallback using translog in peer recoveries if the recovering replica does not have a peer recovery retention lease, and the replication group hasn't fully migrated to PRRL. Relates elastic#45136
dnhatn
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Dec 15, 2019
Today we do not use retention leases in peer recovery for closed indices because we can't sync retention leases on closed indices. This change allows that ability and adjusts peer recovery to use retention leases for all indices with soft-deletes enabled. Relates #45136 Co-authored-by: David Turner <david.turner@elastic.co>
dnhatn
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Dec 15, 2019
Since 7.4, we switch from translog to Lucene as the source of history for peer recoveries. However, we reduce the likelihood of operation-based recoveries when performing a full cluster restart from pre-7.4 because existing copies do not have PPRL. To remedy this issue, we fallback using translog in peer recoveries if the recovering replica does not have a peer recovery retention lease, and the replication group hasn't fully migrated to PRRL. Relates #45136
dnhatn
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Dec 16, 2019
Since 7.4, we switch from translog to Lucene as the source of history for peer recoveries. However, we reduce the likelihood of operation-based recoveries when performing a full cluster restart from pre-7.4 because existing copies do not have PPRL. To remedy this issue, we fallback using translog in peer recoveries if the recovering replica does not have a peer recovery retention lease, and the replication group hasn't fully migrated to PRRL. Relates elastic#45136
dnhatn
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Dec 16, 2019
Since 7.4, we switch from translog to Lucene as the source of history for peer recoveries. However, we reduce the likelihood of operation-based recoveries when performing a full cluster restart from pre-7.4 because existing copies do not have PPRL. To remedy this issue, we fallback using translog in peer recoveries if the recovering replica does not have a peer recovery retention lease, and the replication group hasn't fully migrated to PRRL. Relates #45136
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Dec 20, 2019
…50351) Today, the replica allocator uses peer recovery retention leases to select the best-matched copies when allocating replicas of indices with soft-deletes. We can employ this mechanism for indices without soft-deletes because the retaining sequence number of a PRRL is the persisted global checkpoint (plus one) of that copy. If the primary and replica have the same retaining sequence number, then we should be able to perform a noop recovery. The reason is that we must be retaining translog up to the local checkpoint of the safe commit, which is at most the global checkpoint of either copy). The only limitation is that we might not cancel ongoing file-based recoveries with PRRLs for noop recoveries. We can't make the translog retention policy comply with PRRLs. We also have this problem with soft-deletes if a PRRL is about to expire. Relates #45136 Relates #46959
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Dec 24, 2019
…50351) Today, the replica allocator uses peer recovery retention leases to select the best-matched copies when allocating replicas of indices with soft-deletes. We can employ this mechanism for indices without soft-deletes because the retaining sequence number of a PRRL is the persisted global checkpoint (plus one) of that copy. If the primary and replica have the same retaining sequence number, then we should be able to perform a noop recovery. The reason is that we must be retaining translog up to the local checkpoint of the safe commit, which is at most the global checkpoint of either copy). The only limitation is that we might not cancel ongoing file-based recoveries with PRRLs for noop recoveries. We can't make the translog retention policy comply with PRRLs. We also have this problem with soft-deletes if a PRRL is about to expire. Relates #45136 Relates #46959
SivagurunathanV
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Jan 23, 2020
Since 7.4, we switch from translog to Lucene as the source of history for peer recoveries. However, we reduce the likelihood of operation-based recoveries when performing a full cluster restart from pre-7.4 because existing copies do not have PPRL. To remedy this issue, we fallback using translog in peer recoveries if the recovering replica does not have a peer recovery retention lease, and the replication group hasn't fully migrated to PRRL. Relates elastic#45136
SivagurunathanV
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Jan 23, 2020
…lastic#50351) Today, the replica allocator uses peer recovery retention leases to select the best-matched copies when allocating replicas of indices with soft-deletes. We can employ this mechanism for indices without soft-deletes because the retaining sequence number of a PRRL is the persisted global checkpoint (plus one) of that copy. If the primary and replica have the same retaining sequence number, then we should be able to perform a noop recovery. The reason is that we must be retaining translog up to the local checkpoint of the safe commit, which is at most the global checkpoint of either copy). The only limitation is that we might not cancel ongoing file-based recoveries with PRRLs for noop recoveries. We can't make the translog retention policy comply with PRRLs. We also have this problem with soft-deletes if a PRRL is about to expire. Relates elastic#45136 Relates elastic#46959
This was referenced Feb 3, 2020
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Today we recover a replica by copying operations from the primary's translog.
However we also retain some historical operations in the index itself, as long
as soft-deletes are enabled. This commit adjusts peer recovery to use the
operations in the index for recovery rather than those in the translog, and
ensures that the replication group retains enough history for use in peer
recovery by means of retention leases.
Reverts #38904 and #42211
Relates #41536