Re: need suggestion on querying big tables

On 12/5/22 00:29, Ebin Jozer wrote:
> Hi Team,
> in postgresql 11 version we have two tables of size 435 GB and 347 GB.
> if we query on single table or if we are doing inner join on both the big
> tables, it is not displacing any output, it keeps running
>
> We can see the wait event is IO and directDatafile .
>
> Server Spec : 8 cores and  64GB RAM
> PG config : 53 GB(effective_cache), 12 GB(shared buffer)
>
> can you please suggest some ideas , how we can query on big tables and
> fasten them to get the output??

https://www.postgresql.org/docs/11/runtime-config-query.html

effective_cache_size is how much RAM *a single* query gets. "When setting
this parameter you should consider both *PostgreSQL's shared buffers*".

https://www.postgresql.org/docs/11/runtime-config-resource.html

"a reasonable starting value for *shared_buffers is 25% of the memory* in
your system. There are some workloads where even larger settings for
shared_buffers are effective, but because PostgreSQL also relies on the
operating system cache, *it is unlikely that an allocation of more than 40%
of RAM to shared_buffers will work better* than a smaller amount."

You've set effective_cache_size to 83%, when it should be at most 20%.

--
Angular momentum makes the world go 'round.