Troubleshoot MySQL

For more general information, see how to troubleshoot development.

Lock wait timeout

If a process running in your application acquired a lock from MySQL for a long period of time, you receive MySQL error messages like this:

SQLSTATE[HY000]: General error: 1205 Lock wait timeout exceeded;

This is typically caused by one of the following:

• There are multiple places acquiring locks in different order. For example, code path 1 first locks record A and then locks record B, while code path 2 first locks record B and then locks record A.
• There is a long-running background process executed by your application that holds the lock until it ends.

If you’re using MariaDB 10+, use the SQL query SHOW FULL PROCESSLIST \G to list DB queries waiting for locks. To determine where to debug, find output like the following:

< skipped >
Command: Query
Time: ...
State: Waiting for table metadata lock
Info: SELECT ...
< skipped >

To find active background processes, run ps aufx on your application container.

Make sure that locks are acquired in a pre-defined order and released as soon as possible.

Definer/invoker of view lack rights to use them

There is a single MySQL user, so you cannot use the “DEFINER” Access Control mechanism for Stored Programs and Views.

When creating a VIEW, you may need to explicitly set the SECURITY parameter to INVOKER:

CREATE OR REPLACE SQL SECURITY INVOKER
VIEW `view_name` AS
SELECT

Server has gone away

Disk space issues

Errors such as PDO Exception 'MySQL server has gone away' are usually the result of exhausting your available disk space. Get an estimate of current disk usage using the CLI command platform db:size. Note that this is an estimate, not an exact value.

Allocate more space to the service in .platform/services.yaml. As table space can grow rapidly, set your database mount size to twice the size reported by the db:size command.

Consider adding a low-disk warning to get notified about low disk space before it becomes an issue.

Packet size limitations

MySQL server has gone away errors may be caused by the size of the database packets. If so, the logs may show warnings like Error while sending QUERY packet before the error.

One way to resolve the issue is to use the max_allowed_packet parameter.

Worker timeout

MySQL server has gone away errors may be caused by server timeouts. MySQL has a built-in timeout for idle connections, which defaults to 10 minutes. Most typical web connections end long before that’s ever approached, but a long-running worker may idle and not need the database for longer than the timeout, leading to a “server has gone away” message.

The best approach is to wrap your connection logic in code that detects a “server has gone away” exception and tries to re-establish the connection.

Alternatively, if your worker is idle for too long it can self-terminate. Upsun Fixed automatically restarts the worker process and the new process can establish a new database connection.

Too many connections

You may get the following error message: Error 1040: Too many connections. A common way to solve this issue is to increase the max_connections property in your MariaDB service configuration. However, on Upsun Fixed, you cannot configure max_connections, as it is calculated automatically based on available memory.

The max_connections property cannot be configured in Upsun Fixed service configurations, nor can it be influenced by any other config. It is calculated automatically based on available container memory and increases automatically when the container size increases.

How it works

The following formula determines max_connections for a given container:

        avg_memory_per_connection_mb = 4
        free = container_memory - (50 + container_memory * 0.70)
        max_connections = int(free // avg_memory_per_connection_mb)

The memory for a given container from its size depends on its container profile.

For example, MariaDB has a HIGH_MEMORY container profile. For size: L, this means 0.40 CPU and 1280 MB of memory.

Using the configuration above, where mariadb.size: L is 1280 MB, the calculation becomes:

        avg_memory_per_connection_mb = 4
        free = 1280 - (50 + 1280 * 0.70) # 1280 - 946 = 334
        max_connections = int(free // avg_memory_per_connection_mb) # 334 / 4 = 83.5 -> max_connections = 83