qc_mysqlembedded does not look into functions when collecting
the affected fields of a query. Therefore the affected fields
of a query like
SELECT concat(a, "", "") from X where b = 1;
will be "b" and not "a b" as it should be.
qc_mysqlembedded used Item::next for traversing the fields of WHERE.
That is not correct as next is not intended for that purpose:
/**
Intrusive list pointer for free list. If not null, points to the next
Item on some Query_arena's free list. For instance, stored procedures
have their own Query_arena's.
@see Query_arena::free_list
*/
Item *next;
In pratice this meant that the fields in the SELECT part were reported
twice and that, depending on the query, all fields of WHERE were *not*
reported. For instance, the result for
SELECT a from X WHERE b = 1 and c = 2;
would correctly be "a b c" (in fact, it would be "a b c a"), but
the result for
SELECT a from X WHERE b = 1 and c = 2 and d = 3;
would also be "a b c".
Both the passwords and temporary files of the embedded library were stored
in the same directory. Now the directories are separated and the embedded
library uses the temporary directory. The datadir cleanup also now only
cleans up the temporary data directory.
There can be any sort of library behind qc_init. Hence the arguments
cannot be hardwired to be like the embedded library wants them.
Eventually it might make sense to allow passing arguments from
maxscale.cnf.
The query_classifier library is now only a wrapper that loads an
actual query classifier implementation. Currently it is hardwired
to load qc_mysqlembedded, which implements the query classifier
API using MySQL embedded.
This will be changed, so that the library to load is specified
when qc_init() is called. That will then allow the query classifier
to be specified in the config file.
Currently there seems to be a conflict between the mysql_library_end()
call made in qc_mysqlembedded and the mysql_library_end() call made in
gateway.c. The reason is that they both finalize a shared library.
For the time being mysql_library_end() is not called in gateway.c.
This problem is likely to go away by switching from the client
library to the connector-c library.
Currently not used, but the existing query_classifier will be
changed into being just a wrapper around a dynamically loaded
query classifier plugin, i.e. qc_mysqlembedded.
