We are facing one very serious issue while starting Mysql. We are Using Digital Ocean.

Droplet
RAM = 8GB 
CPU = 4Core
Mysql Version = 5.6

My.cnf

[mysql]
# CLIENT #
port = 3306
socket = /var/lib/mysql/mysql.sock

[mysqld]
max_connections                = 300
open_files_limit               = 1024000
#interactive_timeout           = 30
#wait_timeout              = 30
# GENERAL #
user                           = mysql
default-storage-engine         = InnoDB
socket                         = /var/lib/mysql/mysql.sock
pid-file                       = /var/lib/mysql/mysql.pid

# MyISAM #
key-buffer-size                = 64M
myisam-recover                 = FORCE,BACKUP

# SAFETY #
max-allowed-packet             = 16M
max-connect-errors             = 1000000
skip-name-resolve
sysdate-is-now                 = 1
innodb                         = FORCE

# DATA STORAGE #
datadir                        = /var/lib/mysql/

# BINARY LOGGING #
log-bin                        = /var/lib/mysql/mysql-bin
expire_logs_days               = 10
#expire-logs-days              = 14
sync_binlog                    = 1

# CACHES AND LIMITS #
tmp-table-size                 = 500M
max-heap-table-size            = 500M
query-cache-type               = 0
query-cache-size               = 64M
#max-connections                = 300
thread-cache-size              = 50
#open_files_limit               = 65535
table-definition-cache         = 1024M
table_open_cache               = 600

# INNODB #
innodb-flush-method            = O_DIRECT
innodb-log-files-in-group      = 2
innodb-log-file-size           = 64M
innodb-flush-log-at-trx-commit = 1
innodb-file-per-table          = 1
innodb-buffer-pool-size        = 12000M
innodb-buffer-pool-instances   = 1
join_buffer_size               = 6M

# LOGGING #
log-error                      = /var/lib/mysql/mysql-error.log
log-queries-not-using-indexes  = 1
slow-query-log                 = 1
slow-query-log-file            = /var/lib/mysql/mysql-slow.log
long-query-time            = 5
log-queries-not-using-indexes

We are able to start Mysql without any error.

But when we resize existing Droplet from 8Gb RAM and 4 CPU to 16GB and 8 CPU and did not make any changes in my.cnf but Unable to start MYSQL.

During starting MySql it consume all memory 16GB RAM and 5GB swap.

It show error.

160910 18:15:03 mysqldsafe Starting mysqld daemon with databases from /var/lib/mysql/
2016-09-10 18:15:32 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use –explicitdefaultsfortimestamp server option (see documentation for more details).
2016-09-10 18:15:32 0 [Note] /usr/sbin/mysqld (mysqld 5.6.31-log) starting as process 14643 …
2016-09-10 18:15:32 14643 [Warning] Buffered warning: option ‘tabledefinitioncache’: unsigned value 1073741824 adjusted to 524288

2016-09-10 18:15:32 14643 [Warning] Buffered warning: Could not increase number of max_open_files to more than 1024 (request: 1024000)

2016-09-10 18:15:32 14643 [Warning] Buffered warning: Changed limits: max_connections: 214 (requested 300)

2016-09-10 18:15:32 14643 [Warning] Buffered warning: Changed limits: tableopencache: 400 (requested 600)

2016-09-10 18:15:32 14643 [Warning] Using unique option prefix myisam-recover instead of myisam-recover-options is deprecated and will be removed in a future release. Please use the full name instead.
2016-09-10 18:15:32 14643 [Note] Plugin 'FEDERATED’ is disabled.
2016-09-10 18:15:32 14643 [Warning] The option innodb (skip-innodb) is deprecated and will be removed in a future release
2016-09-10 18:15:32 14643 [Note] InnoDB: Using atomics to ref count buffer pool pages
2016-09-10 18:15:32 14643 [Note] InnoDB: The InnoDB memory heap is disabled
2016-09-10 18:15:32 14643 [Note] InnoDB: Mutexes and rwlocks use GCC atomic builtins
2016-09-10 18:15:32 14643 [Note] InnoDB: Memory barrier is not used
2016-09-10 18:15:32 14643 [Note] InnoDB: Compressed tables use zlib 1.2.3
2016-09-10 18:15:32 14643 [Note] InnoDB: Using Linux native AIO
2016-09-10 18:15:32 14643 [Note] InnoDB: Using CPU crc32 instructions
2016-09-10 18:15:32 14643 [Note] InnoDB: Initializing buffer pool, size = 7.8G
InnoDB: mmap(8585216000 bytes) failed; errno 12
2016-09-10 18:15:32 14643 [ERROR] InnoDB: Cannot allocate memory for the buffer pool
2016-09-10 18:15:32 14643 [ERROR] Plugin 'InnoDB’ init function returned error.
2016-09-10 18:15:32 14643 [ERROR] Plugin 'InnoDB’ registration as a STORAGE ENGINE failed.
2016-09-10 18:15:32 14643 [ERROR] Failed to initialize plugins.
2016-09-10 18:15:32 14643 [ERROR] Aborting
2016-09-10 18:15:32 14643 [Note] Binlog end
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'partition’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'PERFORMANCESCHEMA’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBSYSDATAFILES’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBSYSTABLESPACES’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBSYSFOREIGNCOLS’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBSYSFOREIGN’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBSYSFIELDS’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBSYSCOLUMNS’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBSYSINDEXES’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBSYSTABLESTATS’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBSYSTABLES’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBFTINDEXTABLE’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBFTINDEXCACHE’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBFTCONFIG’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBFTBEINGDELETED’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBFTDELETED’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBFTDEFAULTSTOPWORD’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBMETRICS’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBBUFFERPOOLSTATS’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBBUFFERPAGELRU’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBBUFFERPAGE’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBCMPPERINDEXRESET’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBCMPPERINDEX’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBCMPMEMRESET’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBCMPMEM’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBCMPRESET’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBCMP’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBLOCKWAITS’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBLOCKS’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'INNODBTRX’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'BLACKHOLE’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'ARCHIVE’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'MRGMYISAM’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'MyISAM’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'MEMORY’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'CSV’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'sha256password’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'mysqloldpassword’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'mysqlnativepassword’
2016-09-10 18:15:32 14643 [Note] Shutting down plugin 'binlog’
2016-09-10 18:15:32 14643 [Note] /usr/sbin/mysqld: Shutdown complete
160910 18:15:33 mysqldsafe mysqld from pid file /var/lib/mysql/mysql.pid ended

I am not able to understand why mysql is not able to start even there is no change in any setting.

I have 5GB of Swap memory.

According to me I think its issue with DigitalOcean reason same config is working on 8GB ram but it did not work on 16Gb RAM but they are claiming there is no issue on 16GB droplet.

ALso I would to mentioned that we have installed only mysql no other service.

Please help to get it resolved.

Thanks