Fixing PostgreSQL Error: Out of Shared Memory

Overview

The ‘Out of Shared Memory’ error in PostgreSQL often arises when there isn’t enough shared memory available for a process to complete its task. Shared memory is a system-wide resource with size limits, which are controlled by PostgreSQL’s configuration parameters as well as operating system (OS) settings. Below, we explore reasons for the error and provide a set of solutions.

Understanding the Error

Several factors can lead to the depletion of shared memory:

• High concurrency: Many concurrent transactions can exhaust shared resources, like locks and buffer cache.
• Too many subtransactions: A large number of subtransactions can consume considerable shared memory for tracking.
• Undersized memory settings: Inadequate configuration of memory settings in Postgres can be the culprit.
• Operating System limits: The system’s kernel parameters may limit the shared memory available to PostgreSQL.

Solutions

Increase max_locks_per_transaction

This setting affects the maximum number of locks a single transaction can hold, accounting for shared memory use.

1. Locate the PostgreSQL configuration file, usually ‘postgresql.conf’, and open it for editing.
2. Find the ‘max_locks_per_transaction’ setting and increase its value.
3. Save the file and restart the PostgreSQL service to apply changes.

Performance discussion: Increasing ‘max_locks_per_transaction’ will allocate more shared memory for locks, reducing the likelihood of running out of memory but consuming more system resources.

Advantages: Simple change; often resolves the issue. Drawbacks: Higher memory use; not a systemic solution if the problem arises from other causes.

Adjust shared_buffers

This setting determines the size of memory dedicated to caching data blocks.

1. Follow the steps from solution 1 to access ‘postgresql.conf’.
2. Modify the ‘shared_buffers’ parameter with a higher value.
3. Restart the PostgreSQL service.

Performance discussion: Adequate ‘shared_buffers’ can enhance performance but overly large values might not help due to diminishing returns.

Advantages: Can improve overall database performance. Drawbacks: Excessive values may not be beneficial and could decrease performance.

Tune Operating System Parameters

Modify the kernel settings related to shared memory, such as ‘shmmax’ and ‘shmall’.

1. Edit the ‘/etc/sysctl.conf’ file on Unix-based systems.
2. Adjust parameters like ‘kernel.shmmax’ and ‘kernel.shmall’ to higher values.
3. Reload the kernel parameters using ‘sysctl -p’.

Specific settings will depend on system resources and PostgreSQL requirements.

Performance discussion: Increasing OS limits can avoid ‘Out of Shared Memory’ errors without altering PostgreSQL’s configuration.

Advantages: Addresses the root issue in system settings. Drawbacks: Requires system-level changes, which may necessitate administrative permissions and a holistic understanding of the system’s resources.

Reduce Client Connections

Limit misallocation of shared memory by reducing the number of allowed client connections.

1. Access ‘postgresql.conf’ once more.
2. Decrement the value of the ‘max_connections’ setting.
3. Restart the PostgreSQL service for changes to take effect.

Performance discussion: Fewer connections can lead to better resource allocation but may also restrict your application’s scalability.

Advantages: Quick and controlled resource management. Drawbacks: May not suit applications needing high concurrency.

Final Words

Note that while the aforementioned solutions can alleviate the ‘Out of Shared Memory’ error, they might not be universally effective in all situations. Monitoring resource usage following adjustments is recommended to observe the effect and make further tweaks as necessary.