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Troubleshooting MySQL Crashes: Cannot allocate memory for the buffer pool
Posted 2016-05-20Database2 minutes read (About 363 words)

Troubleshooting MySQL Crashes: Cannot allocate memory for the buffer pool

🌐 日本語で読む

Overview

After installing and starting MySQL and SonarQube on an AWS E2 instance,
I ran into an issue where MySQL kept crashing.

Checking the logs revealed the following errors:

  • /var/log/mysqld.log
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InnoDB: mmap(137363456 bytes) failed; errno 12
[ERROR] InnoDB: Cannot allocate memory for the buffer pool
[ERROR] Plugin 'InnoDB' init function returned error.
[ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE
[ERROR] Unknown/unsupported storage engine: InnoDB
[ERROR] Aborting
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Cannot allocate memory for the buffer pool

Cannot allocate memory to the buffer pool

In short, there isn’t enough memory to allocate.
So let’s create some memory.

Solution 1. Create a swap area

Create the swap area

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// Create an empty file
# dd if=/dev/zero of=/swapfile bs=1M count=1024

// Configure the created empty file as a swap area
# mkswap /swapfile

// Enable the swap area
# swapon /swapfile

Verify the swap area

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# free

              total        used        free      shared  buff/cache   available
Mem:        1015472      833592       66456        1456      115424       54708
Swap:       1048572      491136      557436   ← Confirm that the Swap entry has been added

Restart mysql

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# systemctl restart mysqld

Solution 2. Increase the innodb_buffer_pool_size allocation

Check the currently configured innodb_buffer_pool_size

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$ mysql -u <user> -p<pass> <db>  -e "SHOW VARIABLES LIKE 'innodb_buffer_pool_size'"

+-------------------------+-----------+
| Variable_name           | Value     |
+-------------------------+-----------+
| innodb_buffer_pool_size | 118835956 |
+-------------------------+-----------+

You can see that it is below the 137363456 from the error log.
Let’s increase this allocated memory.

Find the location of my.cnf

The files are searched from left to right, and the first my.cnf that exists is used.
/etc/my.cnf → /etc/mysql/my.cnf → /usr/etc/my.cnf → ~/.my.cnf

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# mysql --help | grep my.cnf
                      order of preference, my.cnf, $MYSQL_TCP_PORT,
/etc/my.cnf /etc/mysql/my.cnf /usr/etc/my.cnf ~/.my.cnf

Add memory

In my case,
there was no innodb_buffer_pool_size setting in my.cnf,
so I added it.

  • my.cnf
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[mysqld]
...
...

# Added the following
innodb_buffer_pool_size = 256M

[mysqld_safe]
...
...

Restart mysql

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# systemctl restart mysqld

Verify that it has increased

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$ mysql -u <user> -p<pass> <db>  -e "SHOW VARIABLES LIKE 'innodb_buffer_pool_size'"

+-------------------------+-----------+
| Variable_name           | Value     |
+-------------------------+-----------+
| innodb_buffer_pool_size | 268435456 |
+-------------------------+-----------+

The error log that had been occurring is now gone.

#
kenzo0107

kenzo0107

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