tracing: default span registry to false

This forced real spans to be created across the board, explaining most of the tracing overhead we saw[^1].

[^1]: cockroachdb#133307

docs/generated/settings/settings-for-tenants.txt

@@ -398,7 +398,7 @@ timeseries.storage.resolution_30m.ttl	duration	2160h0m0s	the maximum age of time
 trace.debug_http_endpoint.enabled (alias: trace.debug.enable)	boolean	false	if set, traces for recent requests can be seen at https://<ui>/debug/requests	application
 trace.opentelemetry.collector	string		address of an OpenTelemetry trace collector to receive traces using the otel gRPC protocol, as <host>:<port>. If no port is specified, 4317 will be used.	application
 trace.snapshot.rate	duration	0s	if non-zero, interval at which background trace snapshots are captured	application
-trace.span_registry.enabled	boolean	true	if set, ongoing traces can be seen at https://<ui>/#/debug/tracez	application
+trace.span_registry.enabled	boolean	false	if set, ongoing traces can be seen at https://<ui>/#/debug/tracez	application
 trace.zipkin.collector	string		the address of a Zipkin instance to receive traces, as <host>:<port>. If no port is specified, 9411 will be used.	application
 ui.database_locality_metadata.enabled	boolean	true	if enabled shows extended locality data about databases and tables in DB Console which can be expensive to compute	application
 ui.display_timezone	enumeration	etc/utc	the timezone used to format timestamps in the ui [etc/utc = 0, america/new_york = 1]	application

docs/generated/settings/settings.html

@@ -356,7 +356,7 @@
 <tr><td><div id="setting-trace-debug-enable" class="anchored"><code>trace.debug_http_endpoint.enabled<br />(alias: trace.debug.enable)</code></div></td><td>boolean</td><td><code>false</code></td><td>if set, traces for recent requests can be seen at https://&lt;ui&gt;/debug/requests</td><td>Serverless/Dedicated/Self-Hosted</td></tr>
 <tr><td><div id="setting-trace-opentelemetry-collector" class="anchored"><code>trace.opentelemetry.collector</code></div></td><td>string</td><td><code></code></td><td>address of an OpenTelemetry trace collector to receive traces using the otel gRPC protocol, as &lt;host&gt;:&lt;port&gt;. If no port is specified, 4317 will be used.</td><td>Serverless/Dedicated/Self-Hosted</td></tr>
 <tr><td><div id="setting-trace-snapshot-rate" class="anchored"><code>trace.snapshot.rate</code></div></td><td>duration</td><td><code>0s</code></td><td>if non-zero, interval at which background trace snapshots are captured</td><td>Serverless/Dedicated/Self-Hosted</td></tr>
-<tr><td><div id="setting-trace-span-registry-enabled" class="anchored"><code>trace.span_registry.enabled</code></div></td><td>boolean</td><td><code>true</code></td><td>if set, ongoing traces can be seen at https://&lt;ui&gt;/#/debug/tracez</td><td>Serverless/Dedicated/Self-Hosted</td></tr>
+<tr><td><div id="setting-trace-span-registry-enabled" class="anchored"><code>trace.span_registry.enabled</code></div></td><td>boolean</td><td><code>false</code></td><td>if set, ongoing traces can be seen at https://&lt;ui&gt;/#/debug/tracez</td><td>Serverless/Dedicated/Self-Hosted</td></tr>
 <tr><td><div id="setting-trace-zipkin-collector" class="anchored"><code>trace.zipkin.collector</code></div></td><td>string</td><td><code></code></td><td>the address of a Zipkin instance to receive traces, as &lt;host&gt;:&lt;port&gt;. If no port is specified, 9411 will be used.</td><td>Serverless/Dedicated/Self-Hosted</td></tr>
 <tr><td><div id="setting-ui-database-locality-metadata-enabled" class="anchored"><code>ui.database_locality_metadata.enabled</code></div></td><td>boolean</td><td><code>true</code></td><td>if enabled shows extended locality data about databases and tables in DB Console which can be expensive to compute</td><td>Serverless/Dedicated/Self-Hosted</td></tr>
 <tr><td><div id="setting-ui-display-timezone" class="anchored"><code>ui.display_timezone</code></div></td><td>enumeration</td><td><code>etc/utc</code></td><td>the timezone used to format timestamps in the ui [etc/utc = 0, america/new_york = 1]</td><td>Serverless/Dedicated/Self-Hosted</td></tr>

pkg/sql/tests/autocommit_extended_protocol_test.go

@@ -166,6 +166,9 @@ func TestErrorDuringExtendedProtocolCommit(t *testing.T) {
 
 	s, db, _ := serverutils.StartServer(t, params)
 	defer s.Stopper().Stop(ctx)
+	// This forces a trace span to have been set up in the BeforeExecute
+	// interceptor above.
+	s.Tracer().SetActiveSpansRegistryEnabled(true)
 
 	conn, err := db.Conn(ctx)
 	require.NoError(t, err)

pkg/util/tracing/tracer.go

@@ -179,7 +179,7 @@ var EnableActiveSpansRegistry = settings.RegisterBoolSetting(
 	settings.ApplicationLevel,
 	"trace.span_registry.enabled",
 	"if set, ongoing traces can be seen at https://<ui>/#/debug/tracez",
-	envutil.EnvOrDefaultBool("COCKROACH_REAL_SPANS", true),
+	envutil.EnvOrDefaultBool("COCKROACH_REAL_SPANS", false),
 	settings.WithPublic)
 
 var periodicSnapshotInterval = settings.RegisterDurationSetting(
@@ -667,7 +667,7 @@ func NewTracerWithOpt(ctx context.Context, opts ...TracerOption) *Tracer {
 		t.spanReusePercent = *o.spanReusePercent
 	}
 	t.testing = o.knobs
-	t.SetActiveSpansRegistryEnabled(o.tracingDefault != TracingModeOnDemand)
+	t.SetActiveSpansRegistryEnabled(o.tracingDefault == TracingModeActiveSpansRegistry)
 	if o.sv != nil {
 		t.configure(ctx, o.sv, o.tracingDefault)
 		forceVerboseSpanRegexp.SetOnChange(o.sv, func(ctx context.Context) {