ApsaraDB RDS:What do I do if the number of slow SQL queries increases because the stats collector process of an ApsaraDB RDS for PostgreSQL instance consumes a large number of CPU resources and causes heavy I/O loads?

Problem description

The number of slow SQL queries on an ApsaraDB RDS for PostgreSQL instance increases because the stats collector process consumes a large number of CPU resources and causes heavy I/O loads.

Causes

If your RDS instance runs PostgreSQL 14 or earlier, the stats collector process is used to write the statistics of the RDS instance to files, and the autovacuum worker process is used to frequently update the statistics. The autovacuum worker process reads the statistics, updates the statistics, and then sends the updated statistics to the stats collector process. Then, the stats collector process writes the updated statistics to files. If autovacuum is frequently called, the autovacuum worker and stats collector processes consume a large number of CPU resources and cause heavy I/O loads. As a result, a large number of slow SQL queries are generated. If autovacuum is called to clean up dead tuples, the cleanup efficiency decreases. This also increases the number of slow SQL queries.

If the number of tables on an RDS instance increases, the size of statistics to be collected increases. As a result, the efficiencies of statistics writes and reads are affected, and a large number of slow SQL queries occur.

Solutions

Short-term solutions

• Execute the VACUUM FREEZE statement at regular intervals to reduce the frequency to call autovacuum.

• Increase the values of parameters such as autovacuum_vacuum_scale_factor and autovacuum_vacuum_insert_scale_factor to reduce the frequency to call autovacuum. For more information, see Modify the parameters of an ApsaraDB RDS for PostgreSQL instance.

• Use Premium Enterprise SSDs (ESSDs) to improve the I/O throughput. You can change the storage type from ESSD to Premium ESSD. For more information, see Change the storage type from ESSD to general ESSD.

Long-term solution

Upgrade the major engine version of your RDS instance to PostgreSQL 15 or later. If your RDS instance runs PostgreSQL 15 or later, the statistics of the RDS instance are stored in the shared memory and the stats collector process is removed. This prevents the consumption of physical I/O resources. For more information about how to upgrade the major engine version of an RDS instance, see Upgrade the major engine version.

References

• Use the slow query log analysis feature

• Use the query governance feature

• Use the automatic SQL optimization feature