cli/demo,cdc: enable rangefeeds by default

Fixes #82719,
which made it annoying to run changefeeds in cockroach demo
as you need to enable rangefeeds twice, once at the system
level. Now cockroach demo enables rangefeeds at startup.

You can override this behavior for performance or to demo
the process of enabling rangefeeds with the flag
`--auto-enable-rangefeeds=false`.

Release note (cli change): cockroach demo now enables rangefeeds by default. You can restore the old behavior with --auto-enable-rangefeeds=false.

pkg/cli/cliflags/flags.go

@@ -1295,6 +1295,12 @@ and the system tenant using the \connect command.`,
 If set, disable enterprise features.`,
 	}
 
+	DemoEnableRangefeeds = FlagInfo{
+		Name: "auto-enable-rangefeeds",
+		Description: `
+If set to false, overrides the default demo behavior of enabling rangefeeds.`,
+	}
+
 	UseEmptyDatabase = FlagInfo{
 		Name:        "empty",
 		Description: `Deprecated in favor of --no-example-database`,

pkg/cli/context.go

@@ -611,6 +611,7 @@ func setDemoContextDefaults() {
 	demoCtx.HTTPPort, _ = strconv.Atoi(base.DefaultHTTPPort)
 	demoCtx.WorkloadMaxQPS = 25
 	demoCtx.Multitenant = true
+	demoCtx.DefaultEnableRangefeeds = true
 
 	demoCtx.disableEnterpriseFeatures = false
 }

pkg/cli/demo.go

@@ -252,6 +252,12 @@ func runDemo(cmd *cobra.Command, gen workload.Generator) (resErr error) {
 	}
 	sqlCtx.ShellCtx.DemoCluster = c
 
+	if demoCtx.DefaultEnableRangefeeds {
+		if err = c.SetClusterSetting(ctx, "kv.rangefeed.enabled", true); err != nil {
+			return clierrorplus.CheckAndMaybeShout(err)
+		}
+	}
+
 	if cliCtx.IsInteractive {
 		cliCtx.PrintfUnlessEmbedded(`#
 # Welcome to the CockroachDB demo database!

pkg/cli/democluster/api.go

@@ -51,6 +51,10 @@ type DemoCluster interface {
 
 	// SetupWorkload initializes the workload generator if defined.
 	SetupWorkload(ctx context.Context) error
+
+	// SetClusterSetting overrides a default cluster setting at system level
+	// and for all tenants.
+	SetClusterSetting(ctx context.Context, setting string, value interface{}) error
 }
 
 // EnableEnterprise is not implemented here in order to keep OSS/BSL builds successful.

pkg/cli/democluster/context.go

@@ -96,6 +96,10 @@ type Context struct {
 	// Multitenant is true if we're starting the demo cluster in
 	// multi-tenant mode.
 	Multitenant bool
+
+	// DefaultEnableRangefeeds is true if rangefeeds should start
+	// out enabled.
+	DefaultEnableRangefeeds bool
 }
 
 // IsInteractive returns true if the demo cluster configuration

pkg/cli/democluster/demo_cluster.go

@@ -1217,6 +1217,26 @@ func (c *transientCluster) maybeEnableMultiTenantMultiRegion(ctx context.Context
 	return nil
 }
 
+func (c *transientCluster) SetClusterSetting(ctx context.Context, setting string, value interface{}) error {
+	storageURL, err := c.getNetworkURLForServer(ctx, 0, false /* includeAppName */, false /* isTenant */)
+	if err != nil {
+		return err
+	}
+	db, err := gosql.Open("postgres", storageURL.ToPQ().String())
+	if err != nil {
+		return err
+	}
+	defer db.Close()
+	_, err = db.Exec(fmt.Sprintf("SET CLUSTER SETTING %s = '%v'", setting, value))
+	if err != nil {
+		return err
+	}
+	if c.demoCtx.Multitenant {
+		_, err = db.Exec(fmt.Sprintf("ALTER TENANT ALL SET CLUSTER SETTING %s = '%v'", setting, value))
+	}
+	return err
+}
+
 func (c *transientCluster) SetupWorkload(ctx context.Context) error {
 	if err := c.maybeEnableMultiTenantMultiRegion(ctx); err != nil {
 		return err

pkg/cli/flags.go

@@ -758,6 +758,7 @@ func init() {
 				"For details, see: "+build.MakeIssueURL(53404))
 
 		cliflagcfg.BoolFlag(f, &demoCtx.disableEnterpriseFeatures, cliflags.DemoNoLicense)
+		cliflagcfg.BoolFlag(f, &demoCtx.DefaultEnableRangefeeds, cliflags.DemoEnableRangefeeds)
 
 		cliflagcfg.BoolFlag(f, &demoCtx.Multitenant, cliflags.DemoMultitenant)
 		// TODO(knz): Currently the multitenant UX for 'demo' is not

pkg/cli/interactive_tests/test_demo_changefeeds.tcl

@@ -0,0 +1,37 @@
+#! /usr/bin/env expect -f
+
+source [file join [file dirname $argv0] common.tcl]
+
+start_test "Demo core changefeed using format=csv"
+spawn $argv demo --format=csv
+
+# We should start in a populated database.
+eexpect "movr>"
+
+# initial_scan=only prevents the changefeed from hanging waiting for more changes. 
+send "CREATE CHANGEFEED FOR users WITH initial_scan='only';\r"
+
+# header for the results of a successful changefeed
+eexpect "table,key,value"
+
+send_eof
+eexpect eof
+
+end_test
+
+start_test "Demo with rangefeeds disabled as they are in real life"
+spawn $argv demo --format=csv --auto-enable-rangefeeds=false
+
+# We should start in a populated database.
+eexpect "movr>"
+
+# initial_scan=only prevents the changefeed from hanging waiting for more changes. 
+send "CREATE CHANGEFEED FOR users WITH initial_scan='only';\r"
+
+# changefeed should fail fast with an informative error.
+eexpect "ERROR: rangefeeds require the kv.rangefeed.enabled setting."
+
+send_eof
+eexpect eof
+
+end_test