SERVER-73735 Fail configuration more gracefully if telemetry is disabled

3 files changed, 47 insertions, 0 deletions

diff --git a/jstests/noPassthroughWithMongod/telemetry_configuration.js b/jstests/noPassthroughWithMongod/telemetry_configuration.js
new file mode 100644
index 00000000000..8d0b6ed68b5
--- /dev/null
+++ b/jstests/noPassthroughWithMongod/telemetry_configuration.js
@@ -0,0 +1,32 @@
+/**
+ * Tests that the telemetry store can be resized if it is configured, and cannot be resized if it is
+ * disabled.
+ */
+(function() {
+"use strict";
+
+load("jstests/libs/feature_flag_util.js");
+
+if (FeatureFlagUtil.isEnabled(db, "Telemetry")) {
+    // The feature flag is enabled - make sure the telemetry store can be configured.
+    const original = assert.commandWorked(
+        db.adminCommand({getParameter: 1, internalQueryConfigureTelemetryCacheSize: 1}));
+    assert(original.hasOwnProperty("internalQueryConfigureTelemetryCacheSize"), original);
+    const originalValue = original.internalQueryConfigureTelemetryCacheSize;
+    try {
+        assert.doesNotThrow(
+            () => db.adminCommand(
+                {setParameter: 1, internalQueryConfigureTelemetryCacheSize: '2MB'}));
+        // Other tests verify that resizing actually affects the data structure size.
+    } finally {
+        assert.doesNotThrow(
+            () => db.adminCommand(
+                {setParameter: 1, internalQueryConfigureTelemetryCacheSize: originalValue}));
+    }
+} else {
+    // The feature flag is disabled - make sure the telemetry store *cannot* be configured.
+    assert.commandFailedWithCode(
+        db.adminCommand({setParameter: 1, internalQueryConfigureTelemetryCacheSize: '2MB'}),
+        7373500);
+}
+}());
diff --git a/src/mongo/db/query/telemetry.cpp b/src/mongo/db/query/telemetry.cpp
index 13471a49c9e..32cca0821c1 100644
--- a/src/mongo/db/query/telemetry.cpp
+++ b/src/mongo/db/query/telemetry.cpp
@@ -183,6 +183,8 @@ ServiceContext::ConstructorActionRegisterer telemetryStoreManagerRegisterer{
             // featureFlags are not allowed to be changed at runtime. Therefore it's not an issue
             // to not create a telemetry store in ConstructorActionRegisterer at start up with the
             // flag off - because the flag can not be turned on at any point afterwards.
+            telemetry_util::telemetryStoreOnParamChangeUpdater(serviceCtx) =
+                std::make_unique<telemetry_util::NoChangesAllowedTelemetryParamUpdater>();
             return;
         }
 
diff --git a/src/mongo/db/query/telemetry_util.h b/src/mongo/db/query/telemetry_util.h
index 0aedd95e26e..133d45f1338 100644
--- a/src/mongo/db/query/telemetry_util.h
+++ b/src/mongo/db/query/telemetry_util.h
@@ -60,6 +60,19 @@ public:
 };
 
 /**
+ * A stub implementation that does not allow changing any parameters - to be used if the telemetry
+ * store is disabled and cannot be re-enabled without restarting, as with a feature flag.
+ */
+class NoChangesAllowedTelemetryParamUpdater : public OnParamChangeUpdater {
+public:
+    void updateCacheSize(ServiceContext* serviceCtx, memory_util::MemorySize memSize) final {
+        uasserted(7373500,
+                  "Cannot configure telemetry store - it is currently disabled and a restart is "
+                  "required to activate.");
+    }
+};
+
+/**
  * Decorated accessor to the 'OnParamChangeUpdater' stored in 'ServiceContext'.
  */
 extern const Decorable<ServiceContext>::Decoration<std::unique_ptr<OnParamChangeUpdater>>