Issue with MySQL Server stopping on Ubuntu

I have two wordpress projects on a droplet having 1GB ram, and today the mysql server stopped two times, which led both sites being unnresponsive. I’ve decreased the value of innodb_buffer_pool_size from 134217728 to 104857600, but that didn’t help. I’ve attached the mysql logs below:

2019-01-16T06:37:29.751611Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details). 2019-01-16T06:37:29.754413Z 0 [Note] /usr/sbin/mysqld (mysqld 5.7.24-0ubuntu0.18.04.1) starting as process 24176 … 2019-01-16T06:37:29.763480Z 0 [Note] InnoDB: PUNCH HOLE support available 2019-01-16T06:37:29.763510Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins 2019-01-16T06:37:29.763515Z 0 [Note] InnoDB: Uses event mutexes 2019-01-16T06:37:29.763520Z 0 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier 2019-01-16T06:37:29.763524Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.11 2019-01-16T06:37:29.763528Z 0 [Note] InnoDB: Using Linux native AIO 2019-01-16T06:37:29.764826Z 0 [Note] InnoDB: Number of pools: 1 2019-01-16T06:37:29.768004Z 0 [Note] InnoDB: Using CPU crc32 instructions 2019-01-16T06:37:29.770837Z 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M 2019-01-16T06:37:29.771629Z 0 [ERROR] InnoDB: mmap(137428992 bytes) failed; errno 12 2019-01-16T06:37:29.771653Z 0 [ERROR] InnoDB: Cannot allocate memory for the buffer pool 2019-01-16T06:37:29.771659Z 0 [ERROR] InnoDB: Plugin initialization aborted with error Generic error 2019-01-16T06:37:29.771666Z 0 [ERROR] Plugin ‘InnoDB’ init function returned error. 2019-01-16T06:37:29.771671Z 0 [ERROR] Plugin ‘InnoDB’ registration as a STORAGE ENGINE failed. 2019-01-16T06:37:29.771676Z 0 [ERROR] Failed to initialize builtin plugins. 2019-01-16T06:37:29.771679Z 0 [ERROR] Aborting

2019-01-16T06:37:29.771701Z 0 [Note] Binlog end 2019-01-16T06:37:29.771767Z 0 [Note] Shutting down plugin ‘CSV’ 2019-01-16T06:37:29.772530Z 0 [Note] /usr/sbin/mysqld: Shutdown complete

and

2019-01-16T12:50:44.967079Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details). 2019-01-16T12:50:44.969612Z 0 [Note] /usr/sbin/mysqld (mysqld 5.7.24-0ubuntu0.18.04.1) starting as process 30672 … 2019-01-16T12:50:44.978445Z 0 [Note] InnoDB: PUNCH HOLE support available 2019-01-16T12:50:44.978482Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins 2019-01-16T12:50:44.978488Z 0 [Note] InnoDB: Uses event mutexes 2019-01-16T12:50:44.978492Z 0 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier 2019-01-16T12:50:44.978497Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.11 2019-01-16T12:50:44.978502Z 0 [Note] InnoDB: Using Linux native AIO 2019-01-16T12:50:44.979849Z 0 [Note] InnoDB: Number of pools: 1 2019-01-16T12:50:44.983044Z 0 [Note] InnoDB: Using CPU crc32 instructions 2019-01-16T12:50:44.985170Z 0 [Note] InnoDB: Initializing buffer pool, total size = 100M, instances = 1, chunk size = 100M 2019-01-16T12:50:44.986343Z 0 [ERROR] InnoDB: mmap(107380736 bytes) failed; errno 12 2019-01-16T12:50:44.986364Z 0 [ERROR] InnoDB: Cannot allocate memory for the buffer pool 2019-01-16T12:50:44.986370Z 0 [ERROR] InnoDB: Plugin initialization aborted with error Generic error 2019-01-16T12:50:44.986380Z 0 [ERROR] Plugin ‘InnoDB’ init function returned error. 2019-01-16T12:50:44.986387Z 0 [ERROR] Plugin ‘InnoDB’ registration as a STORAGE ENGINE failed. 2019-01-16T12:50:44.986394Z 0 [ERROR] Failed to initialize builtin plugins. 2019-01-16T12:50:44.986399Z 0 [ERROR] Aborting

2019-01-16T12:50:44.986427Z 0 [Note] Binlog end 2019-01-16T12:50:44.986486Z 0 [Note] Shutting down plugin ‘CSV’ 2019-01-16T12:50:44.986919Z 0 [Note] /usr/sbin/mysqld: Shutdown complete

Also I’ve noticed that with barely any traffic on the sites, the system uses a lot of memory, which is probably why the server shuts itself:

          total        used        free      shared  buff/cache   available

Mem: 985 566 111 124 307 152 Swap: 0 0 0

Do you have any ideea why this happens and how can I fix the issue with the mysql server?