So what is this particular "background worker" I'm seeing, given that I
have no replication or extensions?
Searching the logs I found entries like the following:
LOG: background worker "parallel worker" (PID 93384) exited with exit code 1
This got logged when I killed a simple SELECT query that took too long
doing parallel seqscans. Could it be that the entry in pg_stat_io named
"background worker" also includes the parallel workers from a SELECT
query?
Thanks,
Dimitris
On Wed, 15 May 2024, Muhammad Imtiaz wrote:
Hi,
In PostgreSQL, the pg_stat_io view provides detailed statistics on I/O operations. Background process perform maintenance tasks and other background operations essential to the functioning of the PostgreSQL database.
They include processes such as:
1. Autovacuum Workers
2. WAL Writer
3. Background Writer
4. Logical Replication Workers
5. Custom Background Workers
In the pg_stat_io view, statistics related to I/O operations performed by these background workers are recorded.
Regards,
Imtiaz
On Wed, 15 May 2024, 01:26 Dimitrios Apostolou, <jimis@xxxxxxx> wrote:
Hello list,
what is the "background worker" in the pg_stat_io statistics view? I'm
reading the documentation but can't figure this one out knowing that it is
not autovacuum or bgwriter. And I'm not aware of any extension I might
have with registered background worker.
Additionally, how can it be evictions > writes? I would expect every
eviction to cause a write.
Finally about "hits", I understand they are reads found in shared_buffers,
so they never registered into the "reads" counter. So is "reads" in
pg_stat_io the equivalent to misses, i.e. the opposite of "hits", the read
attempts not found in the shared_buffers, that needed to be fetched from
the disk (or OS buffercache)?
backend_type | object | context | reads | read_time | writes | write_time | writebacks | writeback_time | extends | extend_time | op_bytes | hits | evictions | reuses | fsyncs | fsync_time | stats_reset
-------------------+---------------+---------+---------+-------------+--------+------------+------------+----------------+---------+-------------+----------+-----------+-----------+--------+--------+------------+-------------------------------
background worker | relation | normal | 5139575 | 2196288.011 | 63277 | 1766.94 | 0 | 0 | 0 | 0 | 8192 | 876913705 | 5139653 | | 0 | 0 | 2024-04-08 08:50:02.971192+00
Thank you in advance,
Dimitris
