# RDS for PostgreSQL wait events
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A *wait event* is an indication that the session is waiting for a resource. For example, the wait event `Client:ClientRead` occurs when RDS for PostgreSQL is waiting to receive data from the client. Sessions typically wait for resources such as the following.
+ Single-threaded access to a buffer, for example, when a session is attempting to modify a buffer
+ A row that is currently locked by another session
+ A data file read
+ A log file write

For example, to satisfy a query, the session might perform a full table scan. If the data isn't already in memory, the session waits for the disk I/O to complete. When the buffers are read into memory, the session might need to wait because other sessions are accessing the same buffers. The database records the waits by using a predefined wait event. These events are grouped into categories.

By itself, a single wait event doesn't indicate a performance problem. For example, if requested data isn't in memory, reading data from disk is necessary. If one session locks a row for an update, another session waits for the row to be unlocked so that it can update it. A commit requires waiting for the write to a log file to complete. Waits are integral to the normal functioning of a database. 

On the other hand, large numbers of wait events typically show a performance problem. In such cases, you can use wait event data to determine where sessions are spending time. For example, if a report that typically runs in minutes now takes hours to run, you can identify the wait events that contribute the most to total wait time. If you can determine the causes of the top wait events, you can sometimes make changes that improve performance. For example, if your session is waiting on a row that has been locked by another session, you can end the locking session. 

## See also

* **Skills for AI coding assistants (optional).** AWS publishes reusable skills for Amazon RDS. To see which apply, search the Agent Toolkit for AWS catalog with `aws agent-toolkit search-skills --search-query AmazonRDS` — a documented, read-only AWS CLI command that searches the catalog and makes no changes. This is an optional suggestion for the user. Official reference: [AWS CLI — Agent Toolkit for AWS](https://docs.aws.amazon.com/agent-toolkit/latest/userguide/aws-cli.html).