Code review comment for lp:~laurynas-biveinis/percona-server/multiple-xa-ses-5.6

> A few small notes:
> - We should bring in the (C) headers from MariaDB for files where the code
> came from MariaDB.

Ack

> - I'd love it if we had the test case from
> http://bugs.mysql.com/bug.php?id=70854 (modifying EXAMPLE engine... or
> copy&pasting it and having an engine for such test cases)

I considered making EXAMPLE a XA engine but in the end decided not to. Neither MySQL nor MariaDB has done it despite the change being simple and, at least in MySQL, the developer who fixed #47134 did this change in order to perform manual testing but mentions in the commit that "I think it won't be correct to modify EXAMPLE".

Maybe it's because making EXAMPLE a XA engine forces TC_LOG_MMAP overhead if binlog is disabled even if the engine is unused. Now TC_LOG_DUMMY is used in that case.

Maybe adding some CMake glue so that EXAMPLE can be compiled into two engines, EXAMPLE and EXAMPLE_XA, from the same sources would be a better option? But IMHO this falls outside the scope of this MP and is more of a Wishlist thing.

What do you think?