roachtest: remove global-seed flag

This flag allows the user to seed the global rng instance
for the entire test suite run. This flag is rarely (never)
used and adds confusion for test writers as they are unsure
if they should use the global seed or the test scoped
COCKROACH_RANDOM_SEED.

This changes the flag to be a ROACHTEST_GLOBAL_SEED env
var which still allows it to be set, but unexposes it from
being used directly in roachtests themselves.

Author: DarrylWong

pkg/cmd/roachtest/roachtestflags/BUILD.bazel

@@ -11,7 +11,6 @@ go_library(
     deps = [
         "//pkg/cmd/roachtest/spec",
         "//pkg/roachprod/vm",
-        "//pkg/util/randutil",
         "@com_github_cockroachdb_errors//:errors",
         "@com_github_spf13_pflag//:pflag",
     ],

pkg/cmd/roachtest/roachtestflags/flags.go

@@ -12,7 +12,6 @@ import (
 
 	"github.com/cockroachdb/cockroach/pkg/cmd/roachtest/spec"
 	"github.com/cockroachdb/cockroach/pkg/roachprod/vm"
-	"github.com/cockroachdb/cockroach/pkg/util/randutil"
 	"github.com/spf13/pflag"
 )
 
@@ -476,12 +475,6 @@ var (
 		Usage: `Percentage of failed tests before all remaining tests are automatically terminated.`,
 	})
 
-	GlobalSeed int64 = randutil.NewPseudoSeed()
-	_                = registerRunFlag(&GlobalSeed, FlagInfo{
-		Name:  "global-seed",
-		Usage: `The global random seed used for all tests.`,
-	})
-
 	ClearClusterCache bool = true
 	_                      = registerRunFlag(&ClearClusterCache, FlagInfo{
 		Name: "clear-cluster-cache",

pkg/cmd/roachtest/run.go

@@ -15,6 +15,7 @@ import (
 	"os/user"
 	"path/filepath"
 	"runtime"
+	"strconv"
 	"strings"
 	"time"
 
@@ -30,6 +31,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/roachprod/logger"
 	"github.com/cockroachdb/cockroach/pkg/util/allstacks"
 	"github.com/cockroachdb/cockroach/pkg/util/leaktest"
+	"github.com/cockroachdb/cockroach/pkg/util/randutil"
 	"github.com/cockroachdb/cockroach/pkg/util/stop"
 	"github.com/cockroachdb/cockroach/pkg/util/timeutil"
 	"github.com/cockroachdb/errors"
@@ -50,8 +52,16 @@ const (
 // runTests is the main function for the run and bench commands.
 // Assumes initRunFlagsBinariesAndLibraries was called.
 func runTests(register func(registry.Registry), filter *registry.TestFilter) error {
+	globalSeed := randutil.NewPseudoSeed()
+	if globalSeedEnv := os.Getenv("ROACHTEST_GLOBAL_SEED"); globalSeedEnv != "" {
+		if parsed, err := strconv.ParseInt(globalSeedEnv, 0, 64); err == nil {
+			globalSeed = parsed
+		} else {
+			return errors.Wrapf(err, "could not parse ROACHTEST_GLOBAL_SEED=%q", globalSeedEnv)
+		}
+	}
 	//lint:ignore SA1019 deprecated
-	rand.Seed(roachtestflags.GlobalSeed)
+	rand.Seed(globalSeed)
 	r := makeTestRegistry()
 
 	// actual registering of tests
@@ -147,7 +157,7 @@ func runTests(register func(registry.Registry), filter *registry.TestFilter) err
 		teamLoader:  team.DefaultLoadTeams,
 	}
 
-	l.Printf("global random seed: %d", roachtestflags.GlobalSeed)
+	l.Printf("global random seed: %d", globalSeed)
 	go func() {
 		if err := http.ListenAndServe(
 			fmt.Sprintf(":%d", roachtestflags.PromPort),