SERVER-27972 Add a featureCompatibilityVersion op observer for database/collection drop

4 files changed, 102 insertions, 0 deletions

diff --git a/jstests/noPassthrough/feature_compatibility_version.js b/jstests/noPassthrough/feature_compatibility_version.js
new file mode 100644
index 00000000000..d9c1368b15b
--- /dev/null
+++ b/jstests/noPassthrough/feature_compatibility_version.js
@@ -0,0 +1,80 @@
+// Tests that manipulating the featureCompatibilityVersion document in admin.system.version changes
+// the value of the featureCompatibilityVersion server parameter.
+
+(function() {
+    "use strict";
+
+    const conn = MongoRunner.runMongod({});
+    assert.neq(null, conn, "mongod was unable to start up");
+
+    let adminDB = conn.getDB("admin");
+
+    // Initially the featureCompatibilityVersion is 3.4.
+    let res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.4", res.featureCompatibilityVersion);
+
+    // Updating the featureCompatibilityVersion document changes the featureCompatibilityVersion
+    // server parameter.
+    assert.writeOK(adminDB.system.version.update({_id: "featureCompatibilityVersion"},
+                                                 {$set: {version: "3.2"}}));
+    res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.2", res.featureCompatibilityVersion);
+
+    assert.writeOK(adminDB.system.version.update({_id: "featureCompatibilityVersion"},
+                                                 {$set: {version: "3.4"}}));
+    res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.4", res.featureCompatibilityVersion);
+
+    // Updating the featureCompatibilityVersion document with an invalid version fails.
+    assert.writeErrorWithCode(adminDB.system.version.update({_id: "featureCompatibilityVersion"},
+                                                            {$set: {version: "3.6"}}),
+                              ErrorCodes.BadValue);
+    res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.4", res.featureCompatibilityVersion);
+
+    // Deleting the featureCompatibilityVersion document changes the featureCompatibilityVersion
+    // server parameter to 3.2.
+    assert.writeOK(adminDB.system.version.remove({_id: "featureCompatibilityVersion"}));
+    res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.2", res.featureCompatibilityVersion);
+
+    // Inserting a featureCompatibilityVersion document with an invalid version fails.
+    assert.writeErrorWithCode(
+        adminDB.system.version.insert({_id: "featureCompatibilityVersion", version: "3.6"}),
+        ErrorCodes.BadValue);
+    res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.2", res.featureCompatibilityVersion);
+
+    // Inserting the featureCompatibilityVersion document changes the featureCompatibilityVersion
+    // server parameter.
+    assert.writeOK(
+        adminDB.system.version.insert({_id: "featureCompatibilityVersion", version: "3.2"}));
+    res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.2", res.featureCompatibilityVersion);
+
+    assert.writeOK(adminDB.system.version.remove({_id: "featureCompatibilityVersion"}));
+    res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.2", res.featureCompatibilityVersion);
+
+    assert.writeOK(
+        adminDB.system.version.insert({_id: "featureCompatibilityVersion", version: "3.4"}));
+    res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.4", res.featureCompatibilityVersion);
+
+    // Dropping the admin database changes the featureCompatibilityVersion server parameter to 3.2.
+    adminDB.dropDatabase();
+    res = adminDB.runCommand({getParameter: 1, featureCompatibilityVersion: 1});
+    assert.commandWorked(res);
+    assert.eq("3.2", res.featureCompatibilityVersion);
+
+    MongoRunner.stopMongod(conn);
+}());
diff --git a/src/mongo/db/commands/feature_compatibility_version.cpp b/src/mongo/db/commands/feature_compatibility_version.cpp
index 73988bef0c7..448e134de22 100644
--- a/src/mongo/db/commands/feature_compatibility_version.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version.cpp
@@ -57,6 +57,7 @@ using repl::UnreplicatedWritesBlock;
 constexpr StringData FeatureCompatibilityVersion::k32IncompatibleIndexName;
 constexpr StringData FeatureCompatibilityVersion::kCollection;
 constexpr StringData FeatureCompatibilityVersion::kCommandName;
+constexpr StringData FeatureCompatibilityVersion::kDatabase;
 constexpr StringData FeatureCompatibilityVersion::kParameterName;
 constexpr StringData FeatureCompatibilityVersion::kVersionField;
 
@@ -352,6 +353,13 @@ void FeatureCompatibilityVersion::onDelete(const BSONObj& doc) {
         ServerGlobalParams::FeatureCompatibility::Version::k32);
 }
 
+void FeatureCompatibilityVersion::onDropCollection() {
+    log() << "setting featureCompatibilityVersion to "
+          << FeatureCompatibilityVersionCommandParser::kVersion32;
+    serverGlobalParams.featureCompatibility.version.store(
+        ServerGlobalParams::FeatureCompatibility::Version::k32);
+}
+
 /**
  * Read-only server parameter for featureCompatibilityVersion.
  */
diff --git a/src/mongo/db/commands/feature_compatibility_version.h b/src/mongo/db/commands/feature_compatibility_version.h
index 46fa8390bb3..4bcb4b56e55 100644
--- a/src/mongo/db/commands/feature_compatibility_version.h
+++ b/src/mongo/db/commands/feature_compatibility_version.h
@@ -50,6 +50,7 @@ public:
     static constexpr StringData k32IncompatibleIndexName = "incompatible_with_version_32"_sd;
     static constexpr StringData kCollection = "admin.system.version"_sd;
     static constexpr StringData kCommandName = "setFeatureCompatibilityVersion"_sd;
+    static constexpr StringData kDatabase = "admin"_sd;
     static constexpr StringData kParameterName = "featureCompatibilityVersion"_sd;
     static constexpr StringData kVersionField = "version"_sd;
 
@@ -85,6 +86,11 @@ public:
      * featureCompatibilityVersion document, resets the server parameter to its default value (3.2).
      */
     static void onDelete(const BSONObj& doc);
+
+    /**
+     * Resets the server parameter to its default value (3.2).
+     */
+    static void onDropCollection();
 };
 
 }  // namespace mongo
diff --git a/src/mongo/db/op_observer_impl.cpp b/src/mongo/db/op_observer_impl.cpp
index e8b796daac2..00560851a7a 100644
--- a/src/mongo/db/op_observer_impl.cpp
+++ b/src/mongo/db/op_observer_impl.cpp
@@ -220,6 +220,10 @@ void OpObserverImpl::onDropDatabase(OperationContext* txn, const std::string& db
 
     repl::logOp(txn, "c", dbName.c_str(), cmdObj, nullptr, false);
 
+    if (NamespaceString(dbName).db() == FeatureCompatibilityVersion::kDatabase) {
+        FeatureCompatibilityVersion::onDropCollection();
+    }
+
     getGlobalAuthorizationManager()->logOp(txn, "c", dbName.c_str(), cmdObj, nullptr);
     logOpForDbHash(txn, dbName.c_str());
 }
@@ -238,6 +242,10 @@ void OpObserverImpl::onDropCollection(OperationContext* txn,
         DurableViewCatalog::onExternalChange(txn, collectionName);
     }
 
+    if (collectionName.ns() == FeatureCompatibilityVersion::kCollection) {
+        FeatureCompatibilityVersion::onDropCollection();
+    }
+
     getGlobalAuthorizationManager()->logOp(txn, "c", dbName.c_str(), cmdObj, nullptr);
 
     auto css = CollectionShardingState::get(txn, collectionName);