Hi parallel worker are used for parallel execution of the queries and you can find the help in the below link.
https://www.postgresql.org/docs/current/how-parallel-query-works.html Its controlled by following parameters. max_worker_processes = 6 max_parallel_workers_per_gather = 3 max_parallel_workers = 6 The limit of concurrent parallel workers for the whole cluster is max_parallel_workers, which must be ≤ max_worker_processes. The limit of parallel workers per query is max_parallel_workers_per_gather. Thanks Kashif Zeeshan Bitnine Global On Wed, May 15, 2024 at 5:59 PM Dimitrios Apostolou <ji...@gmx.net> wrote: > 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, <ji...@gmx.net> 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 > > > > > > > > > > >
