clusterversion,kv: remove PriorReadSummaries

Partially addresses cockroachdb#66544 by removing a cluster version and its associated
dependencies which, for any cluster whose version is at least 21.1, is certain
to be active.

Release justification: cluster version cleanup

pkg/clusterversion/cockroach_versions.go

@@ -210,10 +210,6 @@ const (
 	// are propagated across RPC boundaries independently of their verbosity setting.
 	// This requires a version gate this violates implicit assumptions in v20.2.
 	TracingVerbosityIndependentSemantics
-	// PriorReadSummaries introduces support for the use of read summary objects
-	// to ship information about reads on a range through lease changes and
-	// range merges.
-	PriorReadSummaries
 	// NonVotingReplicas enables the creation of non-voting replicas.
 	NonVotingReplicas
 	// V21_1 is CockroachDB v21.1. It's used for all v21.1.x patch releases.
@@ -375,10 +371,6 @@ var versionsSingleton = keyedVersions{
 		Key:     TracingVerbosityIndependentSemantics,
 		Version: roachpb.Version{Major: 20, Minor: 2, Internal: 28},
 	},
-	{
-		Key:     PriorReadSummaries,
-		Version: roachpb.Version{Major: 20, Minor: 2, Internal: 44},
-	},
 	{
 		Key:     NonVotingReplicas,
 		Version: roachpb.Version{Major: 20, Minor: 2, Internal: 46},

pkg/kv/kvserver/batcheval/cmd_end_transaction.go

@@ -1108,8 +1108,7 @@ func mergeTrigger(
 	// directly in this method. The primary reason why these are different is
 	// because the RHS's persistent read summary may not be up-to-date, as it is
 	// not updated by the SubsumeRequest.
-	readSumActive := rec.ClusterSettings().Version.IsActive(ctx, clusterversion.PriorReadSummaries)
-	if merge.RightReadSummary != nil && readSumActive {
+	if merge.RightReadSummary != nil {
 		mergedSum := merge.RightReadSummary.Clone()
 		if priorSum, err := readsummary.Load(ctx, batch, rec.GetRangeID()); err != nil {
 			return result.Result{}, err

pkg/kv/kvserver/batcheval/cmd_lease.go

@@ -145,8 +145,7 @@ func evalNewLease(
 	// only ever updates in-mem state) but it's easy to get things wrong (in
 	// which case they could easily take a catastrophic turn) and the benefit is
 	// low.
-	readSumActive := rec.ClusterSettings().Version.IsActive(ctx, clusterversion.PriorReadSummaries)
-	if priorReadSum != nil && readSumActive {
+	if priorReadSum != nil {
 		if err := readsummary.Set(ctx, readWriter, rec.GetRangeID(), ms, priorReadSum); err != nil {
 			return newFailedLeaseTrigger(isTransfer), err
 		}

pkg/kv/kvserver/replica_command.go

@@ -19,7 +19,6 @@ import (
 	"time"
 
 	"github.com/cockroachdb/cockroach/pkg/base"
-	"github.com/cockroachdb/cockroach/pkg/clusterversion"
 	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/kv"
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/kvserverbase"
@@ -562,13 +561,6 @@ func (r *Replica) AdminMerge(
 		log.Event(ctx, "merge txn begins")
 		txn.SetDebugName(mergeTxnName)
 
-		// If we aren't certain that all possible nodes in the cluster support a
-		// range merge transaction refreshing its reads while the RHS range is
-		// subsumed, observe the commit timestamp to force a client-side retry.
-		if !r.ClusterSettings().Version.IsActive(ctx, clusterversion.PriorReadSummaries) {
-			_ = txn.CommitTimestamp()
-		}
-
 		// Pipelining might send QueryIntent requests to the RHS after the RHS has
 		// noticed the merge and started blocking all traffic. This causes the merge
 		// transaction to deadlock. Just turn pipelining off; the structure of the

pkg/sql/sem/tree/BUILD.bazel

@@ -116,7 +116,6 @@ go_library(
     visibility = ["//visibility:public"],
     deps = [
         "//pkg/base",
-        "//pkg/clusterversion",
         "//pkg/geo",
         "//pkg/geo/geopb",
         "//pkg/keys",

pkg/sql/sem/tree/as_of.go

@@ -18,7 +18,6 @@ import (
 	"time"
 
 	"github.com/cockroachdb/apd/v2"
-	"github.com/cockroachdb/cockroach/pkg/clusterversion"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgcode"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
 	"github.com/cockroachdb/cockroach/pkg/sql/sessiondata"
@@ -227,9 +226,7 @@ func DatumToHLC(evalCtx *EvalContext, stmtTimestamp time.Time, d Datum) (hlc.Tim
 		s := string(*d)
 		// Parse synthetic flag.
 		syn := false
-		if strings.HasSuffix(s, "?") && evalCtx.Settings.Version.IsActive(evalCtx.Context, clusterversion.PriorReadSummaries) {
-			// NOTE: we don't parse this in mixed-version clusters because v20.2
-			// nodes will not know how to handle synthetic timestamps.
+		if strings.HasSuffix(s, "?") {
 			s = s[:len(s)-1]
 			syn = true
 		}