Listing Collection Names Performance

Vivekanandan_Sakthivelu · September 19, 2024, 2:49am

You can either use runCommand or show collection on terminal to list collections on database . This will not have any performance impact , as the information about the collection is pulled from metadata. Usually this metadata information is kept in memory for fast access .

Ref:

Implementation of List Command

github.com

mongodb/mongo/blob/05e7767cea66a858fbb906b9d01f489e97064ae5/src/mongo/db/commands/list_collections.cpp#L350


      
          void doCheckAuthorization(OperationContext* opCtx) const final {
              AuthorizationSession* authzSession = AuthorizationSession::get(opCtx->getClient());
              uassertStatusOK(authzSession->checkAuthorizedToListCollections(request()));
          }
          
          NamespaceString ns() const final {
              return NamespaceString(request().getDbName());
          }
          
          Reply typedRun(OperationContext* opCtx) final {
              CommandHelpers::handleMarkKillOnClientDisconnect(opCtx);
              unique_ptr<MatchExpression> matcher;
              const auto as = AuthorizationSession::get(opCtx->getClient());
          
              const auto listCollRequest = request();
              const auto dbName = listCollRequest.getDbName();
              const bool nameOnly = listCollRequest.getNameOnly();
              const bool authorizedCollections = listCollRequest.getAuthorizedCollections();
          
              // We need to copy the serialization context from the request to the reply object
              const auto respSerializationContext =

github.com

mongodb/mongo/blob/master/src/mongo/db/catalog/collection_catalog.cpp#L925


      
                  return;
              }
          
              LOGV2_DEBUG(22546, 1, "Reloading view catalog for database", logAttrs(dbName));
          
              uncommittedCatalogUpdates.replaceViewsForDatabase(dbName,
                                                                loadViewsForDatabase(opCtx, *this, dbName));
              PublishCatalogUpdates::ensureRegisteredWithRecoveryUnit(opCtx, uncommittedCatalogUpdates);
          }
          
          const Collection* CollectionCatalog::establishConsistentCollection(
              OperationContext* opCtx,
              const NamespaceStringOrUUID& nssOrUUID,
              boost::optional<Timestamp> readTimestamp) const {
              if (_needsOpenCollection(opCtx, nssOrUUID, readTimestamp)) {
                  auto coll = _openCollection(opCtx, nssOrUUID, readTimestamp);
          
                  // Usually, CappedSnapshots must be established before opening the storage snapshot. Thus,
                  // the lookup must be done from the in-memory catalog. It is possible that the required
                  // CappedSnapshot was not properly established when this operation was collection creation,
                  // because a Collection instance was not found in the in-memory catalog.