Scheduler

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Note: Changes made to the configuration on this page must be explicitly loaded to the runtime to take effect. Please refer to the Admin Commands documentation for details on the LOAD and SAVE commands.

Overview

ProxySQL includes a built-in Scheduler designed to execute external scripts at regular intervals. This powerful feature allows administrators to extend ProxySQL's functionality by automating tasks such as:

• Custom health checks for non-standard backends.
• Dynamic reconfiguration based on external events.
• Advanced monitoring and alerting.
• Interaction with external service discovery tools (Consul, ZooKeeper).

The scheduler runs in its own dedicated thread and can manage multiple concurrent tasks.

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Configuration

The scheduler is configured via the scheduler table in the Admin interface.

Table Schema: scheduler

Column	Type	Description
id	INTEGER	Unique identifier for the task.
active	BOOLEAN	Set to 1 to enable the task, 0 to disable.
interval_ms	INTEGER	The execution interval in milliseconds. (Minimum: 100ms).
filename	VARCHAR	The full path to the executable script or binary.
arg1..arg5	VARCHAR	Optional arguments passed to the script.
comment	VARCHAR	Free-form text for documentation purposes.

Example: Adding a Task

INSERT INTO scheduler (id, active, interval_ms, filename, arg1) 
VALUES (10, 1, 5000, '/usr/local/bin/check_backend.sh', 'hostgroup_1');

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Technical Details

Execution Model

The scheduler uses a non-blocking asynchronous model:

1. Forking: For every task execution, ProxySQL performs a fork().
2. Execution: The child process executes the script using execve() with an empty environment for security.
3. Cleanup: ProxySQL spawns a lightweight, detached thread to perform a non-blocking waitpid(), ensuring no zombie processes are left on the system.

Precision

The scheduler uses monotonic_time() to calculate the next execution run, ensuring that system clock jumps (e.g., via NTP) do not cause unexpected task bursts or delays.

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Activation & Persistence

Like most ProxySQL modules, changes to the scheduler table are not active until loaded.

• To Activate: LOAD SCHEDULER TO RUNTIME
• To Persist: SAVE SCHEDULER TO DISK

See the Admin Commands documentation for more details.

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Security Considerations

• Permissions: The ProxySQL process must have execute permissions on the filename specified.
• Environment: Scripts are executed with an empty environment. Any required variables (like PATH or database credentials) should be explicitly set within the script or passed as arguments.
• Isolation: Scripts run as the same user as the ProxySQL process. Ensure the script itself is secure and follows best practices.

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Apply your changes: Remember to use the appropriate LOAD and SAVE commands to activate and persist your configuration. See the complete Admin Commands reference.