SERVER-67246 Remove size multiple restriction on capped collections

4 files changed, 55 insertions, 2 deletions

diff --git a/src/mongo/db/catalog/collection_options.cpp b/src/mongo/db/catalog/collection_options.cpp
index fe685c330ed..800e08172cb 100644
--- a/src/mongo/db/catalog/collection_options.cpp
+++ b/src/mongo/db/catalog/collection_options.cpp
@@ -48,8 +48,12 @@
 namespace mongo {
 namespace {
 long long adjustCappedSize(long long cappedSize) {
-    cappedSize += 0xff;
-    cappedSize &= 0xffffffffffffff00LL;
+    if (serverGlobalParams.featureCompatibility.isVersionInitialized() &&
+        !feature_flags::gfeatureFlagCappedCollectionsRelaxedSize.isEnabled(
+            serverGlobalParams.featureCompatibility)) {
+        cappedSize += 0xff;
+        cappedSize &= 0xffffffffffffff00LL;
+    }
     return cappedSize;
 }
 
diff --git a/src/mongo/db/catalog/collection_options.idl b/src/mongo/db/catalog/collection_options.idl
index 762e664f57d..d8e5e1b30eb 100644
--- a/src/mongo/db/catalog/collection_options.idl
+++ b/src/mongo/db/catalog/collection_options.idl
@@ -34,6 +34,13 @@ global:
 imports:
     - "mongo/db/basic_types.idl"
 
+feature_flags:
+  featureFlagCappedCollectionsRelaxedSize:
+    description: Enables capped collections to have a size non multiple of 256 bytes.
+    cpp_varname: feature_flags::gfeatureFlagCappedCollectionsRelaxedSize
+    default: true
+    version: 6.2
+
 enums:
     ValidationLevel:
         description: "Determines how strictly MongoDB applies the validation rules to existing documents during an update."
diff --git a/src/mongo/db/catalog/collection_options_test.cpp b/src/mongo/db/catalog/collection_options_test.cpp
index da1b1b2874d..f5df8643cf8 100644
--- a/src/mongo/db/catalog/collection_options_test.cpp
+++ b/src/mongo/db/catalog/collection_options_test.cpp
@@ -99,9 +99,27 @@ TEST(CollectionOptions, ErrorBadMax) {
         CollectionOptions::parse(BSON("capped" << true << "max" << (1LL << 31))).getStatus());
 }
 
+TEST(CollectionOptions, CappedSizeNotRoundUpForAlignment) {
+    serverGlobalParams.mutableFeatureCompatibility.setVersion(
+        multiversion::FeatureCompatibilityVersion::kVersion_6_2);
+    const long long kUnalignedCappedSize = 1000;
+    const long long kAlignedCappedSize = 1000;
+
+    // Check size rounds up to multiple of alignment.
+    auto options = assertGet(
+        CollectionOptions::parse((BSON("capped" << true << "size" << kUnalignedCappedSize))));
+
+    ASSERT_EQUALS(options.capped, true);
+    ASSERT_EQUALS(options.cappedSize, kAlignedCappedSize);
+    ASSERT_EQUALS(options.cappedMaxDocs, 0);
+}
+
 TEST(CollectionOptions, CappedSizeRoundsUpForAlignment) {
+    serverGlobalParams.mutableFeatureCompatibility.setVersion(
+        multiversion::FeatureCompatibilityVersion::kVersion_6_0);
     const long long kUnalignedCappedSize = 1000;
     const long long kAlignedCappedSize = 1024;
+
     // Check size rounds up to multiple of alignment.
     auto options = assertGet(
         CollectionOptions::parse((BSON("capped" << true << "size" << kUnalignedCappedSize))));
diff --git a/src/mongo/db/commands/set_feature_compatibility_version_command.cpp b/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
index 4a5add8b4b2..24839c2ca59 100644
--- a/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
+++ b/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
@@ -674,6 +674,30 @@ private:
                     });
             }
         }
+
+        if (!feature_flags::gfeatureFlagCappedCollectionsRelaxedSize.isEnabled(
+                serverGlobalParams.featureCompatibility)) {
+            for (const auto& dbName : DatabaseHolder::get(opCtx)->getNames()) {
+                Lock::DBLock dbLock(opCtx, dbName, MODE_IX);
+                catalog::forEachCollectionFromDb(
+                    opCtx,
+                    dbName,
+                    MODE_S,
+                    [&](const CollectionPtr& collection) {
+                        uasserted(
+                            ErrorCodes::CannotDowngrade,
+                            str::stream()
+                                << "Cannot downgrade the cluster when there are capped "
+                                   "collection with a size that is non multiple of 256 bytes. "
+                                   "Drop or resize the following collection: '"
+                                << collection->ns() << "'");
+                        return true;
+                    },
+                    [&](const CollectionPtr& collection) {
+                        return collection->isCapped() && collection->getCappedMaxSize() % 256 != 0;
+                    });
+            }
+        }
     }
 
     // This helper function is for any internal server downgrade cleanup, such as dropping