replica_proposal.go

// Copyright 2016 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"
	"fmt"
	"path/filepath"
	"time"
	"unsafe"

	"github.com/cockroachdb/cockroach/pkg/clusterversion"
	"github.com/cockroachdb/cockroach/pkg/keys"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/batcheval/result"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/concurrency"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/kvserverbase"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/kvserverpb"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/readsummary/rspb"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/uncertainty"
	"github.com/cockroachdb/cockroach/pkg/roachpb"
	"github.com/cockroachdb/cockroach/pkg/settings/cluster"
	"github.com/cockroachdb/cockroach/pkg/storage"
	"github.com/cockroachdb/cockroach/pkg/storage/enginepb"
	"github.com/cockroachdb/cockroach/pkg/util"
	"github.com/cockroachdb/cockroach/pkg/util/humanizeutil"
	"github.com/cockroachdb/cockroach/pkg/util/log"
	"github.com/cockroachdb/cockroach/pkg/util/quotapool"
	"github.com/cockroachdb/cockroach/pkg/util/timeutil"
	"github.com/cockroachdb/cockroach/pkg/util/tracing"
	"github.com/cockroachdb/redact"
	"github.com/kr/pretty"
	"golang.org/x/time/rate"
)

// ProposalData is data about a command which allows it to be
// evaluated, proposed to raft, and for the result of the command to
// be returned to the caller.
type ProposalData struct {
	// The caller's context, used for logging proposals, reproposals, message
	// sends, but not command application. In order to enable safely tracing events
	// beneath, modifying this ctx field in *ProposalData requires holding the
	// raftMu.
	ctx context.Context

	// An optional tracing span bound to the proposal. Will be cleaned
	// up when the proposal finishes.
	sp *tracing.Span

	// idKey uniquely identifies this proposal.
	// TODO(andrei): idKey is legacy at this point: We could easily key commands
	// by their MaxLeaseIndex, and doing so should be ok with a stop- the-world
	// migration. However, various test facilities depend on the command ID for
	// e.g. replay protection. Later edit: the MaxLeaseIndex assignment has,
	// however, moved to happen later, at proposal time.
	idKey kvserverbase.CmdIDKey

	// proposedAtTicks is the (logical) time at which this command was
	// last (re-)proposed.
	proposedAtTicks int

	// createdAtTicks is the (logical) time at which this command was
	// *first* proposed.
	createdAtTicks int

	// command is serialized and proposed to raft. In the event of
	// reproposals its MaxLeaseIndex field is mutated.
	command *kvserverpb.RaftCommand

	// encodedCommand is the encoded Raft command, with an optional prefix
	// containing the command ID.
	encodedCommand []byte

	// quotaAlloc is the allocation retrieved from the proposalQuota. Once a
	// proposal has been passed to raft modifying this field requires holding the
	// raftMu. Once the proposal comes out of Raft, ownerwhip of this quota is
	// passed to r.mu.quotaReleaseQueue.
	quotaAlloc *quotapool.IntAlloc

	// ec.done is called after command application to update the timestamp
	// cache and optionally release latches and exits lock wait-queues.
	ec endCmds

	// applied is set when the a command finishes application. It is used to
	// avoid reproposing a failed proposal if an earlier version of the same
	// proposal succeeded in applying.
	applied bool

	// doneCh is used to signal the waiting RPC handler (the contents of
	// proposalResult come from LocalEvalResult).
	//
	// Attention: this channel is not to be signaled directly downstream of Raft.
	// Always use ProposalData.finishApplication().
	doneCh chan proposalResult

	// Local contains the results of evaluating the request tying the upstream
	// evaluation of the request to the downstream application of the command.
	// Nil when the proposal came from another node (i.e. the evaluation wasn't
	// done here).
	Local *result.LocalResult

	// Request is the client's original BatchRequest.
	// TODO(tschottdorf): tests which use TestingCommandFilter use this.
	// Decide how that will work in the future, presumably the
	// CommandFilter would run at proposal time or we allow an opaque
	// struct to be attached to a proposal which is then available as it
	// applies. Other than tests, we only need a few bits of the request
	// here; this could be replaced with isLease and isChangeReplicas
	// booleans.
	Request *roachpb.BatchRequest

	// leaseStatus represents the lease under which the Request was evaluated and
	// under which this proposal is being made. For lease requests, this is the
	// previous lease that the requester was aware of.
	leaseStatus kvserverpb.LeaseStatus

	// tok identifies the request to the propBuf. Once the proposal is made, the
	// token will be used to stop tracking this request.
	tok TrackedRequestToken
}

// finishApplication is called when a command application has finished. The
// method will be called downstream of Raft if the command required consensus,
// but can be called upstream of Raft if the command did not and was never
// proposed.
//
// It first invokes the endCmds function and then sends the specified
// proposalResult on the proposal's done channel. endCmds is invoked here in
// order to allow the original client to be canceled. (When the original client
// is canceled, it won't be listening to this done channel, and so it can't be
// counted on to invoke endCmds itself.)
//
// The method is safe to call more than once, but only the first result will be
// returned to the client.
func (proposal *ProposalData) finishApplication(ctx context.Context, pr proposalResult) {
	proposal.ec.done(ctx, proposal.Request, pr.Reply, pr.Err)
	proposal.signalProposalResult(pr)
	if proposal.sp != nil {
		proposal.sp.Finish()
		proposal.sp = nil
	}
}

// returnProposalResult signals proposal.doneCh with the proposal result if it
// has not already been signaled. The method can be called even before the
// proposal has finished replication and command application, and does not
// release the request's latches.
//
// The method is safe to call more than once, but only the first result will be
// returned to the client.
func (proposal *ProposalData) signalProposalResult(pr proposalResult) {
	if proposal.doneCh != nil {
		proposal.doneCh <- pr
		proposal.doneCh = nil
		// Need to remove any span from the proposal, as the signalled caller
		// will likely finish it, and if we then end up applying this proposal
		// we'll try to make a ChildSpan off `proposal.ctx` and this will
		// trigger the Span use-after-finish assertions.
		//
		// See: https://github.com/cockroachdb/cockroach/pull/76858#issuecomment-1048179588
		//
		// NB: `proposal.ec.repl` might already have been cleared if we arrive here
		// through finishApplication.
		proposal.ctx = context.Background()
	}
}

// releaseQuota releases the proposal's quotaAlloc and sets it to nil.
// If the quotaAlloc is already nil it is a no-op.
func (proposal *ProposalData) releaseQuota() {
	if proposal.quotaAlloc != nil {
		proposal.quotaAlloc.Release()
		proposal.quotaAlloc = nil
	}
}

// leaseJumpOption controls what assertions leasePostApplyLocked can make.
type leaseJumpOption bool

const (
	// assertNoLeaseJump means that the new lease must follow the old lease, with
	// no gaps in the sequence number.
	assertNoLeaseJump leaseJumpOption = false
	// allowLeaseJump meanms that sequence number gaps must be tolerated. This is
	// used when we've found out about the new lease through a snapshot and we
	// don't know what other previous leases we haven't applied.
	allowLeaseJump = true
)

// leasePostApplyLocked updates the Replica's internal state to reflect the
// application of a new Range lease. The method is idempotent, so it can be
// called repeatedly for the same lease safely. However, the method will panic
// if newLease has a lower sequence number than the current lease. Depending on
// jumpOpt, we'll also panic if newLease indicates a forward sequence number
// jump compared to prevLease (i.e. a skipped lease).
//
// prevLease represents the most recent lease this replica was aware of before
// newLease came along. This is usually (but not necessarily) the latest lease
// ever applied to the range. However, there's also the case when the replica
// found out about newLease through a snapshot; in this case the replica might
// not be aware of other lease changes that happened before the snapshot was
// generated. This method thus tolerates prevLease being "stale" when
// allowLeaseJump is passed. prevLease can also be the same as newLease; see
// below.
//
// newLease represents the lease being applied. Can be the same as prevLease.
// This allows leasePostApplyLocked to be called for some of its side-effects
// even if the lease in question has otherwise already been applied to the
// range.
//
// In addition to the leases, the method accepts a summary of the reads served
// on the range by prior leaseholders. This can be used by the new leaseholder
// to ensure that no future writes are allowed to invalidate prior reads. If a
// summary is not provided, the method pessimistically assumes that prior
// leaseholders served reads all the way up to the start of the new lease.
func (r *Replica) leasePostApplyLocked(
	ctx context.Context,
	prevLease, newLease *roachpb.Lease,
	priorReadSum *rspb.ReadSummary,
	jumpOpt leaseJumpOption,
) {
	// Note that we actually install the lease further down in this method.
	// Everything we do before then doesn't need to worry about requests being
	// evaluated under the new lease.

	// Sanity check to make sure that the lease sequence is moving in the right
	// direction.
	if s1, s2 := prevLease.Sequence, newLease.Sequence; s1 != 0 {
		// We're at a version that supports lease sequence numbers.
		switch {
		case s2 < s1:
			log.Fatalf(ctx, "lease sequence inversion, prevLease=%s, newLease=%s",
				redact.Safe(prevLease), redact.Safe(newLease))
		case s2 == s1:
			// If the sequence numbers are the same, make sure they're actually
			// the same lease. This can happen when callers are using
			// leasePostApply for some of its side effects, like with
			// splitPostApply. It can also happen during lease extensions.
			if !prevLease.Equivalent(*newLease) {
				log.Fatalf(ctx, "sequence identical for different leases, prevLease=%s, newLease=%s",
					redact.Safe(prevLease), redact.Safe(newLease))
			}
		case s2 == s1+1:
			// Lease sequence incremented by 1. Expected case.
		case s2 > s1+1 && jumpOpt == assertNoLeaseJump:
			log.Fatalf(ctx, "lease sequence jump, prevLease=%s, newLease=%s",
				redact.Safe(prevLease), redact.Safe(newLease))
		}
	}

	iAmTheLeaseHolder := newLease.Replica.ReplicaID == r.replicaID
	// NB: in the case in which a node restarts, minLeaseProposedTS forces it to
	// get a new lease and we make sure it gets a new sequence number, thus
	// causing the right half of the disjunction to fire so that we update the
	// timestamp cache.
	leaseChangingHands := prevLease.Replica.StoreID != newLease.Replica.StoreID || prevLease.Sequence != newLease.Sequence

	if iAmTheLeaseHolder {
		// Log lease acquisition whenever an Epoch-based lease changes hands (or verbose
		// logging is enabled).
		if newLease.Type() == roachpb.LeaseEpoch && leaseChangingHands || log.V(1) {
			log.VEventf(ctx, 1, "new range lease %s following %s", newLease, prevLease)
		}
	}

	if leaseChangingHands && iAmTheLeaseHolder {
		// When taking over the lease, we need to check whether a merge is in
		// progress, as only the old leaseholder would have been explicitly notified
		// of the merge. If there is a merge in progress, maybeWatchForMerge will
		// arrange to block all traffic to this replica unless the merge aborts.
		if _, err := r.maybeWatchForMergeLocked(ctx); err != nil {
			// We were unable to determine whether a merge was in progress. We cannot
			// safely proceed.
			log.Fatalf(ctx, "failed checking for in-progress merge while installing new lease %s: %s",
				newLease, err)
		}

		// Forward the node clock to the start time of the new lease. This ensures
		// that the leaseholder's clock always leads its lease's start time. For an
		// explanation about why this is needed, see "Cooperative lease transfers"
		// in pkg/util/hlc/doc.go.
		r.Clock().Update(newLease.Start)

		// If this replica is a new holder of the lease, update the timestamp
		// cache. Note that clock offset scenarios are handled via a stasis
		// period inherent in the lease which is documented in the Lease struct.
		//
		// If the Raft entry included a prior read summary then we can use that
		// directly to update the timestamp cache. Otherwise, we pessimistically
		// assume that prior leaseholders served reads all the way up to the
		// start of the new lease.
		//
		// The introduction of lease transfers implies that the previous lease
		// may have been shortened and we are now applying a formally
		// overlapping lease (since the old lease holder has promised not to
		// serve any more requests, this is kosher). This means that we don't
		// use the old lease's expiration but instead use the new lease's start
		// to initialize the timestamp cache low water.
		var sum rspb.ReadSummary
		if priorReadSum != nil {
			sum = *priorReadSum
		} else {
			sum = rspb.FromTimestamp(newLease.Start.ToTimestamp())
		}
		applyReadSummaryToTimestampCache(r.store.tsCache, r.descRLocked(), sum)

		// Reset the request counts used to make lease placement decisions and
		// load-based splitting/merging decisions whenever starting a new lease.
		if r.leaseholderStats != nil {
			r.leaseholderStats.resetRequestCounts()
		}
		r.loadBasedSplitter.Reset(r.Clock().PhysicalTime())
	}

	// Inform the concurrency manager that the lease holder has been updated.
	// We do this before installing the new lease in `r.mu.state` as we have
	// an invariant that any replica with a lease has the concurrency manager
	// enabled. (In practice, since both happen under `r.mu`, it is likely
	// to not matter).
	r.concMgr.OnRangeLeaseUpdated(newLease.Sequence, iAmTheLeaseHolder)

	// Inform the propBuf about the new lease so that it can initialize its closed
	// timestamp tracking.
	r.mu.proposalBuf.OnLeaseChangeLocked(iAmTheLeaseHolder, r.mu.state.RaftClosedTimestamp, r.mu.state.LeaseAppliedIndex)

	// Ordering is critical here. We only install the new lease after we've
	// checked for an in-progress merge and updated the timestamp cache. If the
	// ordering were reversed, it would be possible for requests to see the new
	// lease but not the updated merge or timestamp cache state, which can result
	// in serializability violations.
	r.mu.state.Lease = newLease
	expirationBasedLease := r.requiresExpiringLeaseRLocked()

	// Gossip the first range whenever its lease is acquired. We check to make
	// sure the lease is active so that a trailing replica won't process an old
	// lease request and attempt to gossip the first range.
	now := r.store.Clock().NowAsClockTimestamp()
	if leaseChangingHands && iAmTheLeaseHolder && r.IsFirstRange() && r.ownsValidLeaseRLocked(ctx, now) {
		r.gossipFirstRangeLocked(ctx)
	}

	// Whenever we first acquire an expiration-based lease, notify the lease
	// renewer worker that we want it to keep proactively renewing the lease
	// before it expires.
	if leaseChangingHands && iAmTheLeaseHolder && expirationBasedLease && r.ownsValidLeaseRLocked(ctx, now) {
		r.store.renewableLeases.Store(int64(r.RangeID), unsafe.Pointer(r))
		select {
		case r.store.renewableLeasesSignal <- struct{}{}:
		default:
		}
	}

	// If we're the current raft leader, may want to transfer the leadership to
	// the new leaseholder. Note that this condition is also checked periodically
	// when ticking the replica.
	r.maybeTransferRaftLeadershipToLeaseholderLocked(ctx, now)

	// Notify the store that a lease change occurred and it may need to
	// gossip the updated store descriptor (with updated capacity).
	prevOwner := prevLease.OwnedBy(r.store.StoreID())
	currentOwner := newLease.OwnedBy(r.store.StoreID())
	if leaseChangingHands && (prevOwner || currentOwner) {
		if currentOwner {
			r.store.maybeGossipOnCapacityChange(ctx, leaseAddEvent)
		} else if prevOwner {
			r.store.maybeGossipOnCapacityChange(ctx, leaseRemoveEvent)
		}
		if r.leaseholderStats != nil {
			r.leaseholderStats.resetRequestCounts()
		}
	}

	// Potentially re-gossip if the range contains system data (e.g. system
	// config or node liveness). We need to perform this gossip at startup as
	// soon as possible. Trying to minimize how often we gossip is a fool's
	// errand. The node liveness info will be gossiped frequently (every few
	// seconds) in any case due to the liveness heartbeats. And the system config
	// will be gossiped rarely because it falls on a range with an epoch-based
	// range lease that is only reacquired extremely infrequently.
	if iAmTheLeaseHolder {
		// NB: run these in an async task to keep them out of the critical section
		// (r.mu is held here).
		_ = r.store.stopper.RunAsyncTask(r.AnnotateCtx(context.Background()), "lease-triggers", func(ctx context.Context) {
			// Re-acquire the raftMu, as we are now in an async task.
			r.raftMu.Lock()
			defer r.raftMu.Unlock()
			if _, err := r.IsDestroyed(); err != nil {
				// Nothing to do.
				return
			}
			if err := r.MaybeGossipSystemConfigRaftMuLocked(ctx); err != nil {
				log.Errorf(ctx, "%v", err)
			}
			if err := r.MaybeGossipNodeLivenessRaftMuLocked(ctx, keys.NodeLivenessSpan); err != nil {
				log.Errorf(ctx, "%v", err)
			}
		})
		if leaseChangingHands && log.V(1) {
			// This logging is useful to troubleshoot incomplete drains.
			log.Info(ctx, "is now leaseholder")
		}
	}

	// Inform the store of this lease.
	if iAmTheLeaseHolder {
		r.store.registerLeaseholder(ctx, r, newLease.Sequence)
	} else {
		r.store.unregisterLeaseholder(ctx, r)
	}

	// Mark the new lease in the replica's lease history.
	if r.leaseHistory != nil {
		r.leaseHistory.add(*newLease)
	}
}

var addSSTPreApplyWarn = struct {
	threshold time.Duration
	log.EveryN
}{30 * time.Second, log.Every(5 * time.Second)}

func addSSTablePreApply(
	ctx context.Context,
	st *cluster.Settings,
	eng storage.Engine,
	sideloaded SideloadStorage,
	term, index uint64,
	sst kvserverpb.ReplicatedEvalResult_AddSSTable,
	limiter *rate.Limiter,
) bool {
	checksum := util.CRC32(sst.Data)

	if checksum != sst.CRC32 {
		log.Fatalf(
			ctx,
			"checksum for AddSSTable at index term %d, index %d does not match; at proposal time %x (%d), now %x (%d)",
			term, index, sst.CRC32, sst.CRC32, checksum, checksum,
		)
	}

	path, err := sideloaded.Filename(ctx, index, term)
	if err != nil {
		log.Fatalf(ctx, "sideloaded SSTable at term %d, index %d is missing", term, index)
	}

	tBegin := timeutil.Now()
	var tEndDelayed time.Time
	defer func() {
		if dur := timeutil.Since(tBegin); dur > addSSTPreApplyWarn.threshold && addSSTPreApplyWarn.ShouldLog() {
			log.Infof(ctx,
				"ingesting SST of size %s at index %d took %.2fs (%.2fs on which in PreIngestDelay)",
				humanizeutil.IBytes(int64(len(sst.Data))), index, dur.Seconds(), tEndDelayed.Sub(tBegin).Seconds(),
			)
		}
	}()

	eng.PreIngestDelay(ctx)
	tEndDelayed = timeutil.Now()

	copied := false
	if eng.InMem() {
		// Ingest a copy of the SST. Otherwise, Pebble will claim and mutate the
		// sst.Data byte slice, which will also be used later by e.g. rangefeeds.
		data := make([]byte, len(sst.Data))
		copy(data, sst.Data)
		path = fmt.Sprintf("%x", checksum)
		if err := eng.WriteFile(path, data); err != nil {
			log.Fatalf(ctx, "unable to write sideloaded SSTable at term %d, index %d: %s", term, index, err)
		}
	} else {
		ingestPath := path + ".ingested"

		// The SST may already be on disk, thanks to the sideloading
		// mechanism.  If so we can try to add that file directly, via a new
		// hardlink if the filesystem supports it, rather than writing a new
		// copy of it.  We cannot pass it the path in the sideload store as
		// the engine deletes the passed path on success.
		if linkErr := eng.Link(path, ingestPath); linkErr == nil {
			ingestErr := eng.IngestExternalFiles(ctx, []string{ingestPath})
			if ingestErr != nil {
				log.Fatalf(ctx, "while ingesting %s: %v", ingestPath, ingestErr)
			}
			// Adding without modification succeeded, no copy necessary.
			log.Eventf(ctx, "ingested SSTable at index %d, term %d: %s", index, term, ingestPath)
			return false
		}

		path = ingestPath

		log.Eventf(ctx, "copying SSTable for ingestion at index %d, term %d: %s", index, term, path)

		// TODO(tschottdorf): remove this once sideloaded storage guarantees its
		// existence.
		if err := eng.MkdirAll(filepath.Dir(path)); err != nil {
			panic(err)
		}
		if _, err := eng.Stat(path); err == nil {
			// The file we want to ingest exists. This can happen since the
			// ingestion may apply twice (we ingest before we mark the Raft
			// command as committed). Just unlink the file (the storage engine
			// created a hard link); after that we're free to write it again.
			if err := eng.Remove(path); err != nil {
				log.Fatalf(ctx, "while removing existing file during ingestion of %s: %+v", path, err)
			}
		}

		if err := writeFileSyncing(ctx, path, sst.Data, eng, 0600, st, limiter); err != nil {
			log.Fatalf(ctx, "while ingesting %s: %+v", path, err)
		}
		copied = true
	}

	if err := eng.IngestExternalFiles(ctx, []string{path}); err != nil {
		log.Fatalf(ctx, "while ingesting %s: %+v", path, err)
	}
	log.Eventf(ctx, "ingested SSTable at index %d, term %d: %s", index, term, path)
	return copied
}

func (r *Replica) handleReadWriteLocalEvalResult(ctx context.Context, lResult result.LocalResult) {
	// Fields for which no action is taken in this method are zeroed so that
	// they don't trigger an assertion at the end of the method (which checks
	// that all fields were handled).
	{
		lResult.Reply = nil
	}

	// The caller is required to detach and handle the following three fields.
	if lResult.EncounteredIntents != nil {
		log.Fatalf(ctx, "LocalEvalResult.EncounteredIntents should be nil: %+v", lResult.EncounteredIntents)
	}
	if lResult.EndTxns != nil {
		log.Fatalf(ctx, "LocalEvalResult.EndTxns should be nil: %+v", lResult.EndTxns)
	}

	if lResult.AcquiredLocks != nil {
		for i := range lResult.AcquiredLocks {
			r.concMgr.OnLockAcquired(ctx, &lResult.AcquiredLocks[i])
		}
		lResult.AcquiredLocks = nil
	}

	if lResult.ResolvedLocks != nil {
		for i := range lResult.ResolvedLocks {
			r.concMgr.OnLockUpdated(ctx, &lResult.ResolvedLocks[i])
		}
		lResult.ResolvedLocks = nil
	}

	if lResult.UpdatedTxns != nil {
		for _, txn := range lResult.UpdatedTxns {
			r.concMgr.OnTransactionUpdated(ctx, txn)
		}
		lResult.UpdatedTxns = nil
	}

	if lResult.GossipFirstRange {
		// We need to run the gossip in an async task because gossiping requires
		// the range lease and we'll deadlock if we try to acquire it while
		// holding processRaftMu. Specifically, Replica.redirectOnOrAcquireLease
		// blocks waiting for the lease acquisition to finish but it can't finish
		// because we're not processing raft messages due to holding
		// processRaftMu (and running on the processRaft goroutine).
		if err := r.store.Stopper().RunAsyncTask(
			ctx, "storage.Replica: gossipping first range",
			func(ctx context.Context) {
				hasLease, pErr := r.getLeaseForGossip(ctx)

				if pErr != nil {
					log.Infof(ctx, "unable to gossip first range; hasLease=%t, err=%s", hasLease, pErr)
				} else if !hasLease {
					return
				}
				r.gossipFirstRange(ctx)
			}); err != nil {
			log.Infof(ctx, "unable to gossip first range: %s", err)
		}
		lResult.GossipFirstRange = false
	}

	if lResult.MaybeAddToSplitQueue {
		r.store.splitQueue.MaybeAddAsync(ctx, r, r.store.Clock().NowAsClockTimestamp())
		lResult.MaybeAddToSplitQueue = false
	}

	// The gossip triggers below require raftMu to be held, but
	// handleReadWriteLocalEvalResult() may be called from non-Raft code paths (in
	// particular for noop proposals). LocalResult.RequiresRaft() will force
	// results that set these gossip triggers to always go via Raft such that
	// raftMu is held. The triggers assert that callers hold the mutex during race
	// tests via raftMu.AssertHeld().
	if lResult.MaybeGossipSystemConfig {
		if err := r.MaybeGossipSystemConfigRaftMuLocked(ctx); err != nil {
			log.Errorf(ctx, "%v", err)
		}
		lResult.MaybeGossipSystemConfig = false
	}

	if lResult.MaybeGossipSystemConfigIfHaveFailure {
		if err := r.MaybeGossipSystemConfigIfHaveFailureRaftMuLocked(ctx); err != nil {
			log.Errorf(ctx, "%v", err)
		}
		lResult.MaybeGossipSystemConfigIfHaveFailure = false
	}

	if lResult.MaybeGossipNodeLiveness != nil {
		if err := r.MaybeGossipNodeLivenessRaftMuLocked(ctx, *lResult.MaybeGossipNodeLiveness); err != nil {
			log.Errorf(ctx, "%v", err)
		}
		lResult.MaybeGossipNodeLiveness = nil
	}

	if lResult.Metrics != nil {
		r.store.metrics.handleMetricsResult(ctx, *lResult.Metrics)
		lResult.Metrics = nil
	}

	if !lResult.IsZero() {
		log.Fatalf(ctx, "unhandled field in LocalEvalResult: %s", pretty.Diff(lResult, result.LocalResult{}))
	}
}

// proposalResult indicates the result of a proposal. Exactly one of
// Reply and Err is set, and it represents the result of the proposal.
type proposalResult struct {
	Reply              *roachpb.BatchResponse
	Err                *roachpb.Error
	EncounteredIntents []roachpb.Intent
	EndTxns            []result.EndTxnIntents
}

// evaluateProposal generates a Result from the given request by
// evaluating it, returning both state which is held only on the
// proposer and that which is to be replicated through Raft. The
// return value is ready to be inserted into Replica's proposal map
// and subsequently passed to submitProposalLocked.
//
// The method also returns a flag indicating if the request needs to
// be proposed through Raft and replicated. This flag will be false
// either if the request was a no-op or if it hit an error. In this
// case, the result can be sent directly back to the client without
// going through Raft, but while still handling LocalEvalResult.
//
// Replica.mu must not be held.
func (r *Replica) evaluateProposal(
	ctx context.Context,
	idKey kvserverbase.CmdIDKey,
	ba *roachpb.BatchRequest,
	ui uncertainty.Interval,
	g *concurrency.Guard,
) (*result.Result, bool, *roachpb.Error) {
	if ba.Timestamp.IsEmpty() {
		return nil, false, roachpb.NewErrorf("can't propose Raft command with zero timestamp")
	}

	// Evaluate the commands. If this returns without an error, the batch should
	// be committed. Note that we don't hold any locks at this point, except a
	// shared RLock on raftMuReadOnlyMu. This is important since evaluating a
	// proposal is expensive.
	//
	// Note that, during evaluation, ba's read and write timestamps might get
	// bumped (see evaluateWriteBatchWithServersideRefreshes).
	//
	// TODO(tschottdorf): absorb all returned values in `res` below this point
	// in the call stack as well.
	batch, ms, br, res, pErr := r.evaluateWriteBatch(ctx, idKey, ba, ui, g)

	// Note: reusing the proposer's batch when applying the command on the
	// proposer was explored as an optimization but resulted in no performance
	// benefit.
	if batch != nil {
		defer batch.Close()
	}

	if pErr != nil {
		if _, ok := pErr.GetDetail().(*roachpb.ReplicaCorruptionError); ok {
			return &res, false /* needConsensus */, pErr
		}

		txn := pErr.GetTxn()
		if txn != nil && ba.Txn == nil {
			log.Fatalf(ctx, "error had a txn but batch is non-transactional. Err txn: %s", txn)
		}

		// Failed proposals can't have any Result except for what's
		// allowlisted here.
		res.Local = result.LocalResult{
			EncounteredIntents: res.Local.DetachEncounteredIntents(),
			EndTxns:            res.Local.DetachEndTxns(true /* alwaysOnly */),
			Metrics:            res.Local.Metrics,
		}
		res.Replicated.Reset()
		return &res, false /* needConsensus */, pErr
	}

	// Set the local reply, which is held only on the proposing replica and is
	// returned to the client after the proposal completes, or immediately if
	// replication is not necessary.
	res.Local.Reply = br

	// needConsensus determines if the result needs to be replicated and
	// proposed through Raft. This is necessary if at least one of the
	// following conditions is true:
	// 1. the request created a non-empty write batch.
	// 2. the request had an impact on the MVCCStats. NB: this is possible
	//    even with an empty write batch when stats are recomputed.
	// 3. the request has replicated side-effects.
	// 4. the request is of a type that requires consensus (eg. Barrier).
	// 5. the request has side-effects that must be applied under Raft.
	needConsensus := !batch.Empty() ||
		ms != (enginepb.MVCCStats{}) ||
		!res.Replicated.IsZero() ||
		ba.RequiresConsensus() ||
		res.Local.RequiresRaft()

	if needConsensus {
		log.VEventf(ctx, 2, "need consensus on write batch with op count=%d", batch.Count())

		// Set the proposal's WriteBatch, which is the serialized representation of
		// the proposals effect on RocksDB.
		res.WriteBatch = &kvserverpb.WriteBatch{
			Data: batch.Repr(),
		}

		// Set the proposal's replicated result, which contains metadata and
		// side-effects that are to be replicated to all replicas.
		res.Replicated.IsLeaseRequest = ba.IsLeaseRequest()
		if ba.AppliesTimestampCache() {
			res.Replicated.WriteTimestamp = ba.WriteTimestamp()
		} else {
			if !r.ClusterSettings().Version.IsActive(ctx, clusterversion.DontProposeWriteTimestampForLeaseTransfers) {
				// For misc requests, use WriteTimestamp to propagate a clock signal. This
				// is particularly important for lease transfers, as it assures that the
				// follower getting the lease will have a clock above the start time of
				// its lease.
				//
				// This is no longer needed in v22.1 because nodes running v22.1 and
				// above will update their clock directly from the new lease's start
				// time.
				res.Replicated.WriteTimestamp = r.store.Clock().Now()
			}
		}
		res.Replicated.Delta = ms.ToStatsDelta()

		// This is the result of a migration. See the field for more details.
		if res.Replicated.Delta.ContainsEstimates > 0 {
			res.Replicated.Delta.ContainsEstimates *= 2
		}
	}

	return &res, needConsensus, nil
}

// requestToProposal converts a BatchRequest into a ProposalData, by
// evaluating it. The returned ProposalData is partially valid even
// on a non-nil *roachpb.Error and should be proposed through Raft
// if ProposalData.command is non-nil.
func (r *Replica) requestToProposal(
	ctx context.Context,
	idKey kvserverbase.CmdIDKey,
	ba *roachpb.BatchRequest,
	st kvserverpb.LeaseStatus,
	ui uncertainty.Interval,
	g *concurrency.Guard,
) (*ProposalData, *roachpb.Error) {
	res, needConsensus, pErr := r.evaluateProposal(ctx, idKey, ba, ui, g)

	// Fill out the results even if pErr != nil; we'll return the error below.
	proposal := &ProposalData{
		ctx:         ctx,
		idKey:       idKey,
		doneCh:      make(chan proposalResult, 1),
		Local:       &res.Local,
		Request:     ba,
		leaseStatus: st,
	}

	if needConsensus {
		proposal.command = &kvserverpb.RaftCommand{
			ReplicatedEvalResult: res.Replicated,
			WriteBatch:           res.WriteBatch,
			LogicalOpLog:         res.LogicalOpLog,
			TraceData:            r.getTraceData(ctx),
		}
	}

	return proposal, pErr
}

// getTraceData extracts the SpanMeta of the current span.
func (r *Replica) getTraceData(ctx context.Context) map[string]string {
	sp := tracing.SpanFromContext(ctx)
	if sp == nil {
		return nil
	}
	// TODO(andrei): We should propagate trace info even for non-verbose spans.
	// We'd probably want to use a cheaper mechanism than `InjectMetaInto`,
	// though.
	if !sp.IsVerbose() {
		return nil
	}

	traceCarrier := tracing.MapCarrier{
		Map: make(map[string]string),
	}
	r.AmbientContext.Tracer.InjectMetaInto(sp.Meta(), traceCarrier)
	return traceCarrier.Map
}