Using logs

Log messages can be very helpful with identifying and fixing problems on your application. They can also be used to analyze trends in traffic. Each log serves a different purpose, and you should use different tools and techniques to gather useful data from them.

Understanding errors, warnings, and notices

Logs report entries with three levels of seriousness: errors, warnings, and notices. It's important to know what are the most common causes of log entries and how to resolve them.

You can find more information about using logs in Introduction to troubleshooting with log files.

PHP error log levels

By default, an Acquia Cloud production environment does not log Notice, Strict, or Deprecated entries in the PHP error log. Although these log entries can be helpful during development to identify code that needs to be tested and updated, these types of entries can slow down production environments, by logging and debugging a large amount of potentially unneeded information. On non-production environments, however, all PHP errors are logged, including Notice, Strict, or Deprecated entries.

To change this default behavior and log all PHP messages in the PHP error log for your production environment, add the following code to your settings.php file after the Acquia Require line:

<?php
error_reporting
(E_ALL);
?>

Troubleshooting slow queries

Slow queries in MySQL are frequently the root cause of slowness in Drupal applications. Most often, slow queries are generated either by complex Views or custom code that require MySQL to process a large volume of data.

While it's not ideal to have slow queries on your application, they are not uncommon on many large or complex applications. When they are infrequent or less severe, they will likely go unnoticed for a long period of time. However, if they become more frequent, or get slower over time, they may reach a point where they begin to stack up on each other, causing sudden performance issues and potentially taking the application offline for brief periods of time.

You can see trends in slow queries on the Stack Metrics page. This can be useful for monitoring trends over time, but you will need to take additional steps to analyze this data further by downloading and analyzing the slow query log. For more information, see Downloading a slow query log and Tools for parsing a slow query log.

Avoiding 404 errors

While 404 errors are not uncommon in an application’s logs, if left unaddressed, they can have a severe impact on performance over time. In many cases, you can take simple steps to avoid this issue. For more information, see Avoiding 404 error messages in your logs.

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