Hi
>
> We're seeing SELECT statements and even EXPLAIN (no ANAYLZE)
> statements hang indefinitely until *something* (we don't know what)
> releases some kind of resource or no longer becomes a massive bottle
> neck. These are the symptoms.
Is this in pgAdmin? Or psql on the console?
> However, the system seems healthy - no table ('heavyweight') locks are
> held by any session (this happens with only a few connected sessions),
> all indexes are used correctly, other transactions are writing data (we
> generally only have a few sessions running at a time - perhaps 10) etc.
> etc. In fact, we are writing (or bgwriter is), 2-3 hundred MB/s
> sometimes.
What is shown in "top" and "iostat" whilst the queries are running?
>
> We regularly run vacuum analyze at quiet periods - generally 1-2s daily.
>
> These sessions (that only read data) that are blocked can block from
> anything from between only 5 minutes to 10s of hours then miraculously
> complete successfully at once.
>
Are any "blockers" shown in pg_stat_activity?
>
> checkpoint_segments = 128
> maintenance_work_mem = 256MB
> synchronous_commit = off
> random_page_cost = 3.0
> wal_buffers = 16MB
> shared_buffers = 8192MB
> checkpoint_completion_target = 0.9
> effective_cache_size = 18432MB
> work_mem = 32MB
> effective_io_concurrency = 12
> max_stack_depth = 8MB
> log_autovacuum_min_duration = 0
> log_lock_waits = on
> autovacuum_vacuum_scale_factor = 0.1
> autovacuum_naptime = 8
> autovacuum_max_workers = 4
Memory looks reasonably configured to me. effective_cache_size is only an indication to the planner and is not actually allocated.
Is anything being written to the logfiles?
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