Parameters for logging in Aurora PostgreSQL

You can customize the logging behavior for your Aurora PostgreSQL DB cluster by modifying various parameters. In the following table you can find the parameters that affect how long the logs are stored, when to rotate the log, and whether to output the log as a CSV (comma-separated value) format. You can also find the text output sent to STDERR, among other settings. To change settings for the parameters that are modifiable, use a custom DB cluster parameter group for your Aurora PostgreSQL DB cluster. For more information, see Parameter groups for Amazon Aurora. As noted in the table, the log_line_prefix can't be changed.

To identify application issues, you can look for query failures, login failures, deadlocks, and fatal server errors in the log. For example, suppose that you converted a legacy application from Oracle to Aurora PostgreSQL, but not all queries converted correctly. These incorrectly formatted queries generate error messages that you can find in the logs to help identify problems. For more information about logging queries, see Turning on query logging for your Aurora PostgreSQL DB cluster.

In the following topics, you can find information about how to set various parameters that control the basic details for your PostgreSQL logs.

Setting the log retention period

The rds.log_retention_period parameter specifies how long your Aurora PostgreSQL DB cluster keeps its log files. The default setting is 3 days (4,320 minutes), but you can set this value to anywhere from 1 day (1,440 minutes) to 7 days (10,080 minutes). Be sure that your Aurora PostgreSQL DB cluster has sufficient storage to hold the log files for the period of time.

We recommend that you have your logs routinely published to Amazon CloudWatch Logs so that you can view and analyze system data long after the logs have been removed from your Aurora PostgreSQL DB cluster. For more information, see Publishing Aurora PostgreSQL logs to Amazon CloudWatch Logs. After you set up CloudWatch publishing, Aurora doesn't delete a log until after it's published to CloudWatch Logs.

Amazon Aurora compresses older PostgreSQL logs when storage for the DB instance reaches a threshold. Aurora compresses the files using the gzip compression utility. For more information, see the gzip website.

When storage for the DB instance is low and all available logs are compressed, you get a warning such as the following:

Warning: local storage for PostgreSQL log files is critically low for 
this Aurora PostgreSQL instance, and could lead to a database outage.

If there's not enough storage, Aurora might delete compressed PostgreSQL logs before the end of a specified retention period. If that happens, you see a message similar to the following:

The oldest PostgreSQL log files were deleted due to local storage constraints.

Setting log file rotation

Aurora creates new log files every hour by default. The timing is controlled by the log_rotation_age parameter. This parameter has a default value of 60 (minutes), but you can set it to anywhere from 1 minute to 24 hours (1,440 minutes). When it's time for rotation, a new distinct log file is created. The file is named according to the pattern specified by the log_filename parameter.

Log files can also be rotated according to their size, as specified in the log_rotation_size parameter. This parameter specifies that the log should be rotated when it reaches the specified size (in kilobytes). The default log_rotation_size is 100000 kB (kilobytes) for an Aurora PostgreSQL DB cluster, but you can set this value to anywhere from 50,000 to 1,000,000 kilobytes.

The log file names are based on the file name pattern specified in the log_filename parameter. The available settings for this parameter are as follows:

If you set log_rotation_age parameter to less than 60 minutes, set the log_filename parameter to the minute format.

For more information, see log_rotation_age and log_rotation_size in the PostgreSQL documentation.

Setting the log destination (stderr, csvlog)

By default, Aurora PostgreSQL generates logs in standard error (stderr) format. This format is the default setting for the log_destination parameter. Each message is prefixed using the pattern specified in the log_line_prefix parameter. For more information, see Understanding the log_line_prefix parameter.

Aurora PostgreSQL can also generate the logs in csvlog format. The csvlog is useful for analyzing the log data as comma-separated values (CSV) data. For example, suppose that you use the log_fdw extension to work with your logs as foreign tables. The foreign table created on stderr log files contains a single column with log event data. By adding csvlog to the log_destination parameter, you get the log file in the CSV format with demarcations for the multiple columns of the foreign table. You can now sort and analyze your logs more easily.

If you specify csvlog for this parameter, be aware that both stderr and csvlog files are generated. Be sure to monitor the storage consumed by the logs, taking into account the rds.log_retention_period and other settings that affect log storage and turnover. Using stderr and csvlog more than doubles the storage consumed by the logs.

If you add csvlog to log_destination and you want to revert to the stderr alone, you need to reset the parameter. To do so, open the Amazon RDS Console and then open the custom DB cluster parameter group for your instance. Choose the log_destination parameter, choose Edit parameter, and then choose Reset.

For more information about configuring logging, see Working with Amazon RDS and Aurora PostgreSQL logs: Part 1.

Understanding the log_line_prefix parameter

The stderr log format prefixes each log message with the details specified by the log_line_prefix parameter, as follows.

%t:%r:%u@%d:[%p]:t

You can't change this setting. Each log entry sent to stderr includes the following information.