Tips for Monitoring PostgreSQL for Moodle

Sebastian Insausti


Moodle is a Learning Management System (LMS) designed to provide educators, administrators, and learners with a single robust, secure, and integrated system to create personalized learning environments. It supports different database technologies (e.g. MariaDB, MySQL, PostgreSQL, etc). 

Due to COVID-19, working and studying from home has increased in an exponential way recently, so the availability and performance of this kind of learning platform are getting more important. The only way that you can make sure everything is going fine is by having a good Monitoring and Alerting system in place, but the question is what you need to monitor to ensure that your systems are running in a healthy way.

In this blog, we will take a look at what you need to monitor in a PostgreSQL Moodle Database, and how you can do it easier using ClusterControl.

What to Monitor in PostgreSQL

When monitoring a database node or cluster, there are two main things to take into account: the operating system and the database itself. You will need to define which metrics you are going to monitor from both sides and how you are going to do it. 

Operating System Monitoring

One important thing (which is common to all database engines and even to all systems) is to monitor the Operating System behavior. Here are some points to check here.

CPU Usage

An excessive percentage of CPU usage could be a problem if it is not usual behavior. In this case, is important to identify the process/processes that are generating this issue. If the problem is the database process, you will need to check what is happening inside the database.

RAM Memory or SWAP Usage

If you are seeing a high value for this metric and nothing has changed in your system, you probably need to check your database configuration. Parameters like shared_buffers and work_mem can affect this directly as they define the amount of memory to be able to use for the PostgreSQL database.

Disk Usage

An abnormal increase in the use of disk space or an excessive disk access consumption are important things to monitor as you could have a high number of errors logged in the PostgreSQL log file or a bad cache configuration that could generate an important disk access consumption instead of using memory to process the queries.

Load Average

It is related to the three points mentioned above. A high load average could be generated by excessive CPU, RAM, or disk usage.


A network issue can affect all the systems as the application can’t connect (or connect losing packages) to the database, so this is an important metric to monitor indeed. You can monitor latency or packet loss, and the main issue could be a network saturation, a hardware issue, or just a bad network configuration.

Database Monitoring

Monitoring your PostgreSQL database is not only important to see if you are having an issue, but also to know if you need to change something to improve your database performance, that is probably one of the most important things to monitor in a database. Let’s see some metrics that are important for this.

Query Monitoring

In general, the databases are configured with compatibility and stability in mind by default, so you need to know your queries and his pattern, and configure your databases depending on the traffic that you have. Here, you can use the EXPLAIN command to check the query plan for a specific query, and you can also monitor the amount of SELECT, INSERT, UPDATE, or DELETEs on each node. If you have a long query or a high number of queries running at the same time, that could be a problem for all the systems.

Active Sessions

You should also monitor the number of active sessions. If you are near the limit, you need to check if something is wrong or if you just need to increment the max connection value in the database configuration. The difference in the number can be an increase or decrease of connections. Bad usage of connection pooling, locking, or network issues are the most common problems related to the number of connections.


If you have a query waiting for another query, you need to check if that other query is a normal process or something new. In some cases, if somebody is making an update on a big table, for example, this action can be affecting the normal behavior of your database, generating a high number of locks.


The key metrics to monitor for replication are the lag and the replication state. The most common issues are networking issues, hardware resource issues, or under dimensioning issues. If you are facing a replication issue you will need to know this asap as you will need to fix it to ensure the high availability environment.


Avoiding data loss is one of the basic DBA tasks, so you don’t only need to take the backup, you should know if the backup was completed, and if it is usable. Usually, this last point is not taken into account, but it is probably the most important check in a backup process.

Database Logs

You should monitor your database log for errors, authentication issues, or even long-running queries. Most of the errors are written in the log file with detailed useful information to fix them.

Notifications & Alerting

Just monitoring a system is not enough if you don’t receive a notification about each issue. Without an alerting system, you should go to the monitoring tool to see if everything is fine, and it could be possible that you are having a big issue since many hours ago. This alerting job could be done by using email alerts, text alerts, or other tools like Slack.

Monitoring Your PostgreSQL Moodle Database with ClusterControl

ClusterControl is a management and monitoring system that helps to deploy, manage, monitor, and scale your databases from a friendly interface. ClusterControl has support for the top open-source database technologies and you can automate many of the database tasks you have to perform regularly like adding and scaling new nodes, running backups and restores, and more.

It allows you to monitor your servers in real-time with a predefined set of dashboards to analyze some of the most common metrics.

It allows you to customize the graphs available in the cluster, and you can enable the agent-based monitoring to generate more detailed dashboards. 

You can also create alerts, which inform you of events in your cluster, or integrate it with different services such as PagerDuty or Slack.

In the query monitor section, you can find the top queries, the running queries, queries outliers, and the queries statistics to monitor your database traffic. 

For backup management, ClusterControl centralizes it to protect, secure, and recover your data, and with the verification backup feature, you can confirm if the backup is good to go.

This verification backup job will restore the backup in a separate standalone host, so you can make sure that the backup is working.

Finally, you don’t need to access your database node to check the logs, you can find all your database logs centralized in the ClusterControl Log section.

As you can see, you can handle all the mentioned things from the same centralized system: ClusterControl.

Monitoring with the ClusterControl Command Line

For scripting and automating tasks, or even if you just prefer the command line, ClusterControl has the s9s tool. It is a command-line tool for managing your database cluster.

Cluster List

Node List

You can perform all the tasks that you are able to see in the ClusterControl UI (and even more), and you can integrate this feature with some external tools like slack, to manage it from there.


Monitoring your Moodle PostgreSQL Database is necessary but also a time-consuming task if you don’t have any tool to help with this. In this blog, we mentioned some key metrics to monitor in your Moodle PostgreSQL database, and how to keep your systems under control by using ClusterControl.

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