SERVER-36329 Deprecate failIndexKeyTooLong server parameter

3 files changed, 16 insertions, 4 deletions

diff --git a/src/mongo/db/catalog/private/record_store_validate_adaptor.cpp b/src/mongo/db/catalog/private/record_store_validate_adaptor.cpp
index cc52362502a..d4619c81592 100644
--- a/src/mongo/db/catalog/private/record_store_validate_adaptor.cpp
+++ b/src/mongo/db/catalog/private/record_store_validate_adaptor.cpp
@@ -222,7 +222,7 @@ void RecordStoreValidateAdaptor::validateIndexKeyCount(IndexDescriptor* idx,
     auto totalKeys = numLongKeys + numIndexedKeys;
 
     bool hasTooFewKeys = false;
-    bool noErrorOnTooFewKeys = !failIndexKeyTooLong.load() && (_level != kValidateFull);
+    bool noErrorOnTooFewKeys = !failIndexKeyTooLongParam() && (_level != kValidateFull);
 
     if (idx->isIdIndex() && totalKeys != numRecs) {
         hasTooFewKeys = totalKeys < numRecs ? true : hasTooFewKeys;
diff --git a/src/mongo/db/index/index_access_method.cpp b/src/mongo/db/index/index_access_method.cpp
index 04ebed5b623..4dab655cfb7 100644
--- a/src/mongo/db/index/index_access_method.cpp
+++ b/src/mongo/db/index/index_access_method.cpp
@@ -78,8 +78,20 @@ bool isMultikeyFromPaths(const MultikeyPaths& multikeyPaths) {
 }
 
 }  // namespace
+
+// TODO SERVER-36386: Remove the server parameter
 MONGO_EXPORT_SERVER_PARAMETER(failIndexKeyTooLong, bool, true);
 
+// TODO SERVER-36386: Remove the server parameter
+bool failIndexKeyTooLongParam() {
+    // Always return true in FCV 4.2 although FCV 4.2 actually never needs to
+    // check this value because there shouldn't be any KeyTooLong errors in FCV 4.2.
+    if (serverGlobalParams.featureCompatibility.getVersion() ==
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42)
+        return true;
+    return failIndexKeyTooLong.load();
+}
+
 class BtreeExternalSortComparison {
 public:
     BtreeExternalSortComparison(const BSONObj& ordering, IndexVersion version)
@@ -110,7 +122,7 @@ bool IndexAccessMethod::ignoreKeyTooLong(OperationContext* opCtx) {
     const auto shouldRelaxConstraints =
         repl::ReplicationCoordinator::get(opCtx)->shouldRelaxIndexConstraints(
             opCtx, NamespaceString(_btreeState->ns()));
-    return shouldRelaxConstraints || !failIndexKeyTooLong.load();
+    return shouldRelaxConstraints || !failIndexKeyTooLongParam();
 }
 
 // Find the keys for obj, put them in the tree pointing to loc
diff --git a/src/mongo/db/index/index_access_method.h b/src/mongo/db/index/index_access_method.h
index feb51712f1a..9e1e3185247 100644
--- a/src/mongo/db/index/index_access_method.h
+++ b/src/mongo/db/index/index_access_method.h
@@ -42,13 +42,13 @@
 
 namespace mongo {
 
-extern AtomicBool failIndexKeyTooLong;
-
 class BSONObjBuilder;
 class MatchExpression;
 class UpdateTicket;
 struct InsertDeleteOptions;
 
+bool failIndexKeyTooLongParam();
+
 /**
  * An IndexAccessMethod is the interface through which all the mutation, lookup, and
  * traversal of index entries is done. The class is designed so that the underlying index