The BgWriter process in PostgreSQL is responsible for flushing dirty pages from the shared buffer pool to disk. As such, it is a critical component of the database system and it is important to monitor its activity to ensure it is operating efficiently. One aspect of this monitoring is the use of BgWriter latches.
BgWriter latches are used to provide synchronization between the BgWriter process and other threads accessing the shared buffer pool. Monitoring these latches can provide insight into the performance of the BgWriter process and the overall health of the database system.
To monitor BgWriter latches in PostgreSQL, you can use the following query:
SELECT
name,
count_mode,
wait_mode,
granted,
count,
wait_sum,
wait_max
FROM pg_stat_latch
WHERE mode = ‘ExclusiveLock’ AND name LIKE ‘BgWriter%’
ORDER BY wait_sum DESC;
This query will return a list of BgWriter latches that are currently held in exclusive mode. The count_mode column indicates the number of times the latch has been acquired, while the wait_mode column indicates the mode in which the latch is being waited on. The granted column indicates whether the latch has been granted, and the count column indicates the total number of times the latch has been granted. The wait_sum column indicates the total amount of time (in microseconds) that processes have waited on the latch, and the wait_max column indicates the longest wait time (in microseconds) for any process.
By looking at the wait_sum and wait_max columns, you can identify BgWriter latches that are causing significant delays and investigate the cause of the delays. This information can be useful in tuning the database system and optimizing its performance.
