Viewing temporary file usage with Performance Insights - Amazon Relational Database Service

Viewing temporary file usage with Performance Insights

You can use Performance Insights to view temporary file usage by turning on the metrics temp_bytes and temp_files. The view in Performance Insights doesn't show the specific queries that generate temporary files, however, when you combine Performance Insights with the query shown for pg_ls_tmpdir, you can troubleshoot, analyze, and determine the changes in your query workload.

  1. In the Performance Insights dashboard, choose Manage Metrics.

  2. Choose Database metrics, and select the temp_bytes and temp_files metrics as shown in the following image.

    Metrics displayed in the graph.

  3. In the Top SQL tab, choose the Preferences icon.

  4. In the Preferences window, turn on the following statistics to appear in the Top SQLtab and choose Continue.

    • Temp writes/sec

    • Temp reads/sec

    • Tmp blk write/call

    • Tmp blk read/call

  5. The temporary file is broken out when combined with the query shown for pg_ls_tmpdir, as shown in the following example.

    Query that displays the temporary file usage.

The IO:BufFileRead and IO:BufFileWrite events occur when the top queries in your workload often create temporary files. You can use Performance Insights to identify top queries waiting on IO:BufFileRead and IO:BufFileWrite by reviewing Average Active Session (AAS) in Database Load and Top SQL sections.

IO:BufFileRead and IO:BufFileWrite in the graph.

For more information on how to analyze top queries and load by wait event with Performance Insights, see Overview of the Top SQL tab. You should identify and tune the queries that cause increase in temporary file usage and related wait events. For more information on these wait events and remediation, see IO:BufFileRead and IO:BufFileWrite.

Note

The work_mem parameter controls when the sort operation runs out of memory and results are written into temporary files. We recommend that you don't change the setting of this parameter higher than the default value because it would permit every database session to consume more memory. Also, a single session that performs complex joins and sorts can perform parallel operations in which each operation consumes memory.

As a best practice, when you have a large report with multiple joins and sorts, set this parameter at the session level by using the SET work_mem command. Then the change is only applied to the current session and doesn't change the value globally.