store_merge.go

// Copyright 2019 The Cockroach Authors.
//
// Use of this software is governed by the Business Source License
// included in the file licenses/BSL.txt.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0, included in the file
// licenses/APL.txt.

package kvserver

import (
	"context"

	"github.com/cockroachdb/cockroach/pkg/roachpb"
	"github.com/cockroachdb/cockroach/pkg/util/hlc"
	"github.com/cockroachdb/errors"
)

// MergeRange expands the left-hand replica, leftRepl, to absorb the right-hand
// replica, identified by rightDesc. freezeStart specifies the time at which the
// right-hand replica promised to stop serving traffic and is used to initialize
// the timestamp cache's low water mark for the right-hand keyspace. The
// right-hand replica must exist on this store and the raftMus for both the
// left-hand and right-hand replicas must be held.
func (s *Store) MergeRange(
	ctx context.Context,
	leftRepl *Replica,
	newLeftDesc, rightDesc roachpb.RangeDescriptor,
	freezeStart hlc.Timestamp,
) error {
	if oldLeftDesc := leftRepl.Desc(); !oldLeftDesc.EndKey.Less(newLeftDesc.EndKey) {
		return errors.Errorf("the new end key is not greater than the current one: %+v <= %+v",
			newLeftDesc.EndKey, oldLeftDesc.EndKey)
	}

	rightRepl, err := s.GetReplica(rightDesc.RangeID)
	if err != nil {
		return err
	}

	leftRepl.raftMu.AssertHeld()
	rightRepl.raftMu.AssertHeld()

	if err := rightRepl.postDestroyRaftMuLocked(ctx, rightRepl.GetMVCCStats()); err != nil {
		return err
	}

	// Note that we were called (indirectly) from raft processing so we must
	// call removeInitializedReplicaRaftMuLocked directly to avoid deadlocking
	// on the right-hand replica's raftMu.
	if err := s.removeInitializedReplicaRaftMuLocked(ctx, rightRepl, rightDesc.NextReplicaID, RemoveOptions{
		// The replica was destroyed when the merge applied by to the tombstones
		// added to the batch in runPreApplyTriggersAfterStagingWriteBatch.
		DestroyData: false,
	}); err != nil {
		return errors.Errorf("cannot remove range: %s", err)
	}

	if leftRepl.leaseholderStats != nil {
		leftRepl.leaseholderStats.resetRequestCounts()
	}
	if leftRepl.writeStats != nil {
		// Note: this could be drastically improved by adding a replicaStats method
		// that merges stats. Resetting stats is typically bad for the rebalancing
		// logic that depends on them.
		leftRepl.writeStats.resetRequestCounts()
	}

	// Clear the concurrency manager's lock and txn wait-queues to redirect the
	// queued transactions to the left-hand replica, if necessary.
	rightRepl.concMgr.OnRangeMerge()

	leftLease, _ := leftRepl.GetLease()
	rightLease, _ := rightRepl.GetLease()
	if leftLease.OwnedBy(s.Ident.StoreID) && !rightLease.OwnedBy(s.Ident.StoreID) {
		// We hold the lease for the LHS, but do not hold the lease for the RHS.
		// That means we don't have up-to-date timestamp cache entries for the
		// keyspace previously owned by the RHS. Bump the low water mark for the RHS
		// keyspace to freezeStart, the time at which the RHS promised to stop
		// serving traffic, as freezeStart is guaranteed to be greater than any
		// entry in the RHS's timestamp cache.
		//
		// Note that we need to update our clock with freezeStart to preserve the
		// invariant that our clock is always greater than or equal to any
		// timestamps in the timestamp cache. For a full discussion, see the comment
		// on TestStoreRangeMergeTimestampCacheCausality.
		s.Clock().Update(freezeStart)
		setTimestampCacheLowWaterMark(s.tsCache, &rightDesc, freezeStart)
	}

	// Update the subsuming range's descriptor.
	leftRepl.setDescRaftMuLocked(ctx, &newLeftDesc)
	return nil
}