From the very beginning, the default InnoDB transaction isolation level
REPEATABLE READ does not correspond to any well formed definition.
The main issue is the lack of write/write conflict detection.
To fix that and to make REPEATABLE READ correspond to Snapshot Isolation,
b8a6719889 introduced the Boolean
session variable innodb_snapshot_isolation. It was disabled by default
in order not to break any user applications.
In a new major version of MariaDB Server, we had better enable this
parameter by default.
BY A CONCURRENT TRANSACTIO
The member function QUICK_RANGE_SELECT::init_ror_merged_scan() performs
a table handler clone. Innodb does not provide a clone operation.
The ha_innobase::clone() is not there. The handler::clone() does not
take care of the ha_innobase->prebuilt->select_lock_type. Because of
this what happens is that for one index we do a locking read, and
for the other index we were doing a non-locking (consistent) read.
The patch introduces ha_innobase::clone() member function.
It is implemented similar to ha_myisam::clone(). It calls the
base class handler::clone() and then does any additional operation
required. I am setting the ha_innobase->prebuilt->select_lock_type
correctly.
rb://1060 approved by Marko
