# Parameters for logging in Aurora PostgreSQL
<a name="USER_LogAccess.Concepts.PostgreSQL.overview.parameter-groups"></a>

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](USER_WorkingWithParamGroups.md). 


| Parameter | Default | Description | 
| --- | --- | --- | 
| log\$1destination | stderr | Sets the output format for the log. The default is `stderr` but you can also specify comma-separated value (CSV) by adding `csvlog` to the setting. For more information, see [Setting the log destination (`stderr`, `csvlog`)](#USER_LogAccess.Concepts.PostgreSQL.Log_Format).  | 
| log\$1filename | postgresql.log.%Y-%m-%d-%H%M  | Specifies the pattern for the log file name. In addition to the default, this parameter supports `postgresql.log.%Y-%m-%d` and `postgresql.log.%Y-%m-%d-%H` for the filename pattern. For Aurora PostgreSQL version 17.4 and later, you can't modify this parameter.  | 
| log\$1line\$1prefix | %t:%r:%u@%d:[%p]: | Defines the prefix for each log line that gets written to `stderr`, to note the time (%t), remote host (%r), user (%u), database (%d), and process ID (%p). | 
| log\$1rotation\$1age | 60 | Minutes after which log file is automatically rotated. You can change this value within the range of 1 and 1440 minutes. For more information, see [Setting log file rotation](#USER_LogAccess.Concepts.PostgreSQL.log_rotation).  | 
| log\$1rotation\$1size | – | The size (kB) at which the log is automatically rotated. You can change this value within the range of 50,000 to 1,000,000 kilobytes. To learn more, see [Setting log file rotation](#USER_LogAccess.Concepts.PostgreSQL.log_rotation). | 
| rds.log\$1retention\$1period | 4320 | PostgreSQL logs that are older than the specified number of minutes are deleted. The default value of 4320 minutes deletes log files after 3 days. For more information, see [Setting the log retention period](#USER_LogAccess.Concepts.PostgreSQL.log_retention_period). | 

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 ](USER_LogAccess.Concepts.PostgreSQL.Query_Logging.md). 

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

**Topics**
+ [Setting the log retention period](#USER_LogAccess.Concepts.PostgreSQL.log_retention_period)
+ [Setting log file rotation](#USER_LogAccess.Concepts.PostgreSQL.log_rotation)
+ [Setting the log destination (`stderr`, `csvlog`)](#USER_LogAccess.Concepts.PostgreSQL.Log_Format)
+ [Understanding the log\$1line\$1prefix parameter](#USER_LogAccess.Concepts.PostgreSQL.Log_Format.log-line-prefix)

## Setting the log retention period
<a name="USER_LogAccess.Concepts.PostgreSQL.log_retention_period"></a>

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](AuroraPostgreSQL.CloudWatch.md). 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](https://www.gzip.org) 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
<a name="USER_LogAccess.Concepts.PostgreSQL.log_rotation"></a>

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:
+ `postgresql.log.%Y-%m-%d` – Default format for the log file name. Includes the year, month, and date in the name of the log file.
+ `postgresql.log.%Y-%m-%d-%H` – Includes the hour in the log file name format.
+ `postgresql.log.%Y-%m-%d-%H%M` – Includes hour:minute in the log file name format.

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 [https://www.postgresql.org/docs/current/runtime-config-logging.html#GUC-LOG-ROTATION-AGE](https://www.postgresql.org/docs/current/runtime-config-logging.html#GUC-LOG-ROTATION-AGE) and [https://www.postgresql.org/docs/current/runtime-config-logging.html#GUC-LOG-ROTATION-SIZE](https://www.postgresql.org/docs/current/runtime-config-logging.html#GUC-LOG-ROTATION-SIZE) in the PostgreSQL documentation.

## Setting the log destination (`stderr`, `csvlog`)
<a name="USER_LogAccess.Concepts.PostgreSQL.Log_Format"></a>

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\$1line\$1prefix parameter](#USER_LogAccess.Concepts.PostgreSQL.Log_Format.log-line-prefix). 

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](https://aws.amazon.com/blogs/database/working-with-rds-and-aurora-postgresql-logs-part-1/).

## Understanding the log\$1line\$1prefix parameter
<a name="USER_LogAccess.Concepts.PostgreSQL.Log_Format.log-line-prefix"></a>

The `stderr` log format prefixes each log message with the details specified by the `log_line_prefix` parameter. The default value is:

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

Starting from Aurora PostgreSQL version 16, you can also choose:

```
%m:%r:%u@%d:[%p]:%l:%e:%s:%v:%x:%c:%q%a
```

Each log entry sent to stderr includes the following information based on the selected value:
+ `%t` – Time of log entry without milliseconds
+ `%m` – Time of log entry with milliseconds
+  `%r` – Remote host address
+  `%u@%d` – User name @ database name
+  `[%p]` – Process ID if available
+  `%l` – Log line number per session 
+  `%e` – SQL error code 
+  `%s` – Process start timestamp 
+  `%v` – Virtual transaction id 
+  `%x` – Transaction ID 
+  `%c` – Session ID 
+  `%q` – Non-session terminator 
+  `%a` – Application name