default dataset-size too large, mariadb fails to start

[Kevin W Monroe]

The default 'dataset-size' on the mariadb charm is 80% of the system memory. On an 8GB ppc64le machine, mariadb fails to start when deployed to a lxc container. Error from /var/log/mysql/error.log:

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160519 21:54:19 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
160519 22:01:46 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
160519 22:01:46 [Note] /usr/sbin/mysqld (mysqld 5.5.49-MariaDB-1ubuntu0.14.04.1) starting as process 27810 ...
/usr/sbin/mysqld: Query cache is disabled (resize or similar command in progress); repeat this command later
160519 22:01:46 InnoDB: The InnoDB memory heap is disabled
160519 22:01:46 InnoDB: Mutexes and rw_locks use GCC atomic builtins
160519 22:01:46 InnoDB: Compressed tables use zlib 1.2.8
160519 22:01:46 InnoDB: Using Linux native AIO
160519 22:01:46 InnoDB: Initializing buffer pool, size = 6.4G
InnoDB: mmap(7025590272 bytes) failed; errno 12
160519 22:01:46 InnoDB: Completed initialization of buffer pool
160519 22:01:46 InnoDB: Fatal error: cannot allocate memory for the buffer pool
160519 22:01:46 [ERROR] Plugin 'InnoDB' init function returned error.
160519 22:01:46 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
160519 22:01:46 [Note] Plugin 'FEEDBACK' is disabled.
160519 22:01:46 [ERROR] Unknown/unsupported storage engine: InnoDB
160519 22:01:46 [ERROR] Aborting
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This is happening with mariadb-server-5.5, which is the community version that gets installed on ppc64le by default. I am able to get the service to start successfully if i turn down the dataset-size to 50%:

juju set-config mariadb dataset-size=50%

This bug is to request the dataset-size be lowered so the default deployment works without any user intervention.