kvserverbase: allow MMA cluster setting in production builds

Previously, the `kv.allocator.load_based_rebalancing` cluster setting
could only be set to "multi-metric only" or "multi-metric and count"
in test builds or when the `COCKROACH_ALLOW_MMA` environment variable
was set.

Remove this restriction to allow MMA (multi-metric allocation) to be
enabled in production. Also remove references to the now-unnecessary
`COCKROACH_ALLOW_MMA` env var from roachtests and drtprod configs.

Fixes: #159587
Epic: CRDB-55052

Author: tbg

pkg/cmd/drtprod/configs/drt_scale_300.yaml

@@ -80,8 +80,6 @@ targets:
           - "COCKROACH_TESTING_FORCE_RELEASE_BRANCH=true"
           - "--env" # from defaults
           - "COCKROACH_INTERNAL_DISABLE_METAMORPHIC_TESTING=true"
-          - "--env" # for MMA test case scenario
-          - "COCKROACH_ALLOW_MMA=true"
         flags:
           # add flag to set provisioned throughput on each store according to their cloud provider limits
           enable-fluent-sink: true

pkg/cmd/roachtest/tests/allocation_bench.go

@@ -302,7 +302,6 @@ func setupAllocationBench(
 	for i := 1; i <= spec.nodes; i++ {
 		// Don't start a backup schedule as this test reports to roachperf.
 		settings := install.MakeClusterSettings()
-		settings.Env = append(settings.Env, "COCKROACH_ALLOW_MMA=true")
 		startOpts := option.NewStartOpts(option.NoBackupSchedule)
 		startOpts.RoachprodOpts.ExtraArgs = append(startOpts.RoachprodOpts.ExtraArgs,
 			"--vmodule=store_rebalancer=2,allocator=2,replicate_queue=2")

pkg/kv/kvserver/kvserverbase/BUILD.bazel

@@ -21,11 +21,8 @@ go_library(
         "//pkg/roachpb",
         "//pkg/settings",
         "//pkg/settings/cluster",
-        "//pkg/util/buildutil",
         "//pkg/util/debugutil",
-        "//pkg/util/envutil",
         "//pkg/util/errorutil",
-        "//pkg/util/errorutil/unimplemented",
         "//pkg/util/hlc",
         "//pkg/util/log",
         "//pkg/util/quotapool",

pkg/kv/kvserver/kvserverbase/base.go

@@ -17,9 +17,6 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/raft/raftpb"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
 	"github.com/cockroachdb/cockroach/pkg/settings"
-	"github.com/cockroachdb/cockroach/pkg/util/buildutil"
-	"github.com/cockroachdb/cockroach/pkg/util/envutil"
-	"github.com/cockroachdb/cockroach/pkg/util/errorutil/unimplemented"
 	"github.com/cockroachdb/cockroach/pkg/util/quotapool"
 	"github.com/cockroachdb/redact"
 )
@@ -115,8 +112,6 @@ var MVCCGCQueueEnabled = settings.RegisterBoolSetting(
 	true,
 )
 
-var allowMMA = envutil.EnvOrDefaultBool("COCKROACH_ALLOW_MMA", false)
-
 // LoadBasedRebalancingMode controls whether range rebalancing takes
 // additional variables such as write load and disk usage into account.
 // If disabled, rebalancing is done purely based on replica count.
@@ -133,14 +128,6 @@ var LoadBasedRebalancingMode = settings.RegisterEnumSetting(
 		LBRebalancingMultiMetricAndCount: "multi-metric and count",
 	},
 	settings.WithPublic,
-	settings.WithValidateEnum(func(enumStr string) error {
-		isMMA := enumStr == "multi-metric and count" || enumStr == "multi-metric only"
-		if buildutil.CrdbTestBuild || !isMMA || allowMMA {
-			return nil
-		}
-		return unimplemented.NewWithIssue(
-			103320, "multi-metric rebalancing not supported for production use")
-	}),
 )
 
 // LoadBasedRebalancingModeIsMMA returns true if the load-based rebalancing mode