* issue 511.9.1: track DataSource instance instead of only its name in QueryCache
* address use of invalid function
* fix expected test result
* address merge issue
* get rid of memory stores
* do not use 'waitForSync' transaction option to synchronize a view
* honor `Methods::isSingleOperationTransaction()` hint
* explicitly specify index_writer's properties
* ensure data is synced
* fix tests
* another fix
* code cleanup
* remove code duplication
* some fixes
* fix typo