cli/demo: pre-load 'movr' by default

Release note (cli change): `cockroach demo` without argument becomes
equivalent to `cockroach demo movr`. The previous behavior
(no pre-defined dataset) is still available via `cockroach demo
--empty`.

pkg/cli/cli_test.go

@@ -473,6 +473,7 @@ func Example_demo() {
 
 	testData := [][]string{
 		{`demo`, `-e`, `show database`},
+		{`demo`, `-e`, `show database`, `--empty`},
 		{`demo`, `-e`, `show application_name`},
 		{`demo`, `--format=table`, `-e`, `show database`},
 		{`demo`, `-e`, `select 1 as "1"`, `-e`, `select 3 as "3"`},
@@ -488,14 +489,17 @@ func Example_demo() {
 	// Output:
 	// demo -e show database
 	// database
+	// movr
+	// demo -e show database --empty
+	// database
 	// defaultdb
 	// demo -e show application_name
 	// application_name
 	// $ cockroach demo
 	// demo --format=table -e show database
 	//   database
-	// +-----------+
-	//   defaultdb
+	// +----------+
+	//   movr
 	// (1 row)
 	// demo -e select 1 as "1" -e select 3 as "3"
 	// 1

pkg/cli/cliflags/flags.go

@@ -795,6 +795,13 @@ The line length where sqlfmt will try to wrap.`,
 		Description: `How many in-memory nodes to create for the demo.`,
 	}
 
+	UseEmptyDatabase = FlagInfo{
+		Name: "empty",
+		Description: `
+Start with an empty database: avoid pre-loading a default dataset in
+the demo shell.`,
+	}
+
 	LogDir = FlagInfo{
 		Name: "log-dir",
 		Description: `

pkg/cli/context.go

@@ -146,6 +146,9 @@ func initCLIDefaults() {
 	networkBenchCtx.port = 8081
 	networkBenchCtx.addresses = []string{"localhost:8081"}
 
+	demoCtx.nodes = 1
+	demoCtx.useEmptyDatabase = false
+
 	initPreFlagsDefaults()
 
 	// Clear the "Changed" state of all the registered command-line flags.
@@ -339,5 +342,6 @@ var sqlfmtCtx struct {
 // demoCtx captures the command-line parameters of the `demo` command.
 // Defaults set by InitCLIDefaults() above.
 var demoCtx struct {
-	nodes int
+	nodes            int
+	useEmptyDatabase bool
 }

pkg/cli/demo.go

@@ -39,17 +39,30 @@ var demoCmd = &cobra.Command{
 Start an in-memory, standalone, single-node CockroachDB instance, and open an
 interactive SQL prompt to it. Various datasets are available to be preloaded as
 subcommands: e.g. "cockroach demo startrek". See --help for a full list.
-`,
+
+By default, the 'movr' dataset is pre-loaded. You can also use --empty
+to avoid pre-loading a dataset.`,
 	Example: `  cockroach demo`,
 	Args:    cobra.NoArgs,
 	RunE: MaybeDecorateGRPCError(func(cmd *cobra.Command, _ []string) error {
 		return runDemo(cmd, nil /* gen */)
 	}),
 }
 
+const defaultGeneratorName = "movr"
+
+var defaultGenerator workload.Generator
+
 func init() {
 	for _, meta := range workload.Registered() {
 		gen := meta.New()
+
+		if meta.Name == defaultGeneratorName {
+			// Save the default for use in the top-level 'demo' command
+			// without argument.
+			defaultGenerator = gen
+		}
+
 		var genFlags *pflag.FlagSet
 		if f, ok := gen.(workload.Flagser); ok {
 			genFlags = f.Flags().FlagSet
@@ -168,6 +181,11 @@ func setupTransientServers(
 }
 
 func runDemo(cmd *cobra.Command, gen workload.Generator) error {
+	if gen == nil && !demoCtx.useEmptyDatabase {
+		// Use a default dataset unless prevented by --empty.
+		gen = defaultGenerator
+	}
+
 	connURL, adminURL, cleanup, err := setupTransientServers(cmd, gen)
 	defer cleanup()
 	if err != nil {

pkg/cli/flags.go

@@ -541,6 +541,9 @@ func init() {
 	// We add this command as a persistent flag so you can do stuff like
 	// ./cockroach demo movr --nodes=3.
 	IntFlag(demoFlags, &demoCtx.nodes, cliflags.DemoNodes, 1)
+	// The --empty flag is only valid for the top level demo command,
+	// so we use the regular flag set.
+	BoolFlag(demoCmd.Flags(), &demoCtx.useEmptyDatabase, cliflags.UseEmptyDatabase, false)
 
 	// sqlfmt command.
 	fmtFlags := sqlfmtCmd.Flags()

pkg/cli/interactive_tests/test_demo.tcl

@@ -16,6 +16,6 @@ eexpect "Cluster ID"
 eexpect "brief introduction"
 # Ensure user is root.
 eexpect root@
-# Ensure db is defaultdb.
-eexpect "defaultdb>"
+# Ensure db is movr.
+eexpect "movr>"
 end_test