EC2 Instance - Wordpress database keeps crashing - mysql

Question

Im not sure why this is but my Wordpress Site keeps crashing with the "There was an error establishing a database connection" error.
Restarting the mysql service seems to temporarily fix this problem but it inevitably crashes again and again.
I thought it may be a memory issue so I upgraded my instance from 1gb to 2gb. But nothing seems to have changed.. I'd rather not pay the massive extra cost for this if it isn't memory related.
Here is some of the mysql log file relating to the crash. All the crashes seem to contain the following:
160519 13:03:21 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
160519 13:03:21 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
160519 13:03:21 [Note] /usr/libexec/mysql55/mysqld (mysqld 5.5.46) starting as process 18275 ...
160519 13:03:21 [Note] Plugin 'FEDERATED' is disabled.
160519 13:03:21 InnoDB: The InnoDB memory heap is disabled
160519 13:03:21 InnoDB: Mutexes and rw_locks use GCC atomic builtins
160519 13:03:21 InnoDB: Compressed tables use zlib 1.2.8
160519 13:03:21 InnoDB: Using Linux native AIO
160519 13:03:21 InnoDB: Initializing buffer pool, size = 128.0M
InnoDB: mmap(137363456 bytes) failed; errno 12
160519 13:03:21 InnoDB: Completed initialization of buffer pool
160519 13:03:21 InnoDB: Fatal error: cannot allocate memory for the buffer pool
160519 13:03:21 [ERROR] Plugin 'InnoDB' init function returned error.
160519 13:03:21 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
160519 13:03:21 [ERROR] Unknown/unsupported storage engine: InnoDB
160519 13:03:21 [ERROR] Aborting
160519 13:03:21 [Note] /usr/libexec/mysql55/mysqld: Shutdown complete
****UPDATE****
So I have changed the size of the innodb_buffer_pool_size as mentioned below and also made a swapfile. My site still crashes every few hours and I am slowly losing the will to live.
160507 16:28:20 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
160507 16:28:20 [Note] /usr/libexec/mysql55/mysqld (mysqld 5.5.46) starting as process 26457 ...
160507 16:28:20 [Note] Plugin 'FEDERATED' is disabled.
160507 16:28:20 InnoDB: The InnoDB memory heap is disabled
160507 16:28:20 InnoDB: Mutexes and rw_locks use GCC atomic builtins
160507 16:28:20 InnoDB: Compressed tables use zlib 1.2.8
160507 16:28:20 InnoDB: Using Linux native AIO
160507 16:28:20 InnoDB: Initializing buffer pool, size = 128.0M
160507 16:28:20 InnoDB: Completed initialization of buffer pool
InnoDB: The first specified data file ./ibdata1 did not exist:
InnoDB: a new database to be created!
160507 16:28:20 InnoDB: Setting file ./ibdata1 size to 10 MB
InnoDB: Database physically writes the file full: wait...
160507 16:28:21 InnoDB: Log file ./ib_logfile0 did not exist: new to be created
InnoDB: Setting log file ./ib_logfile0 size to 5 MB
InnoDB: Database physically writes the file full: wait...
160507 16:28:21 InnoDB: Log file ./ib_logfile1 did not exist: new to be created
InnoDB: Setting log file ./ib_logfile1 size to 5 MB
InnoDB: Database physically writes the file full: wait...
InnoDB: Doublewrite buffer not found: creating new
InnoDB: Doublewrite buffer created
InnoDB: 127 rollback segment(s) active.
InnoDB: Creating foreign key constraint system tables
InnoDB: Foreign key constraint system tables created
160507 16:28:21 InnoDB: Waiting for the background threads to start
160507 16:28:22 InnoDB: 5.5.46 started; log sequence number 0
160507 16:28:22 [Note] Server hostname (bind-address): '0.0.0.0'; port: 3306
160507 16:28:22 [Note] - '0.0.0.0' resolves to '0.0.0.0';
160507 16:28:22 [Note] Server socket created on IP: '0.0.0.0'.
160507 16:28:22 [Note] Event Scheduler: Loaded 0 events
160507 16:28:22 [Note] /usr/libexec/mysql55/mysqld: ready for connections.
Version: '5.5.46' socket: '/var/lib/mysql/mysql.sock' port: 3306 MySQL Community Server (GPL)
160507 17:56:05 [Note] /usr/libexec/mysql55/mysqld: Normal shutdown
160507 17:56:05 [Note] Event Scheduler: Purging the queue. 0 events
160507 17:56:05 InnoDB: Starting shutdown...
160507 17:56:06 InnoDB: Shutdown completed; log sequence number 2733606
160507 17:56:06 [Note] /usr/libexec/mysql55/mysqld: Shutdown complete

Answer 1

Your buffer size is too high. It probably does not need to be that size, see this answer on dba.stackexchange.com
https://dba.stackexchange.com/questions/27328/how-large-should-be-mysql-innodb-buffer-pool-size
If you are using Amazon Linux, according to mysql docs (https://dev.mysql.com/doc/refman/5.7/en/ha-vm-aws-setup.html) the setting for this is in /etc/my.cnf
Probably altering the setting in this file to innodb_buffer_pool_size = 10M would fix your problem
The above fixes the specific problem shown in the logs above. If there is another problem being logged which concerns memory use then add a 4GiB swapfile with these commands
/bin/dd if=/dev/zero of=/swapfile bs=1M count=4096; /sbin/mkswap /swapfile; /sbin/swapon /swapfile
Using swap isn't magic it will allow your system to run slow and bloated. However, if this gets you over "blips" in memory usage, it could be good