Re: How to calculate how too much memory ram need a PostgreSQL Server?

On 4/5/2021 14:21, DrakoRod wrote:
> Hi folks!!
>
> I support a PostgreSQL database it grew from 100 to 300 GB in couple months,
> I we need tuning all OS parameters (is a virtual enviroment). Currently
the
> configuration is the follow:
>
> Virtual Machine
> Ubuntu 18.04
> 12 CPUS
> 8 GB in RAM
> 400 in Disk
> Clúster database size 320 GB
>
> Some queries have times too differents, the same query sometimes it execute
> in 8 10 seconds sometimes in 12 15 minutes, many querys make joins between
> 40, 50 millions rows. I know some factors like relation between entities
> affect times, but in general I suspect the mainly problem si resources in
> OS.
>
> I suspect is a lack to memory ram but we need justify the change in OS RAM,
> so, How to calculate how too much memory ram need a PostgreSQL Server? Too
> need know how because the database size continue grows.
>
> Best Regards
> DrakoRod

IMHO you need to profile the workload (e.g. "Explain analyze" on the
queries in question), look at the indices in use and whether the planner
can be helped with additional ones on the tables and then look at the
size of said indices and how all of this fits into the RAM you have and
what storage is behind it ( RAM -> SSD -> spinning rust.)

When the working set of the indices required for the queries in question
(not so much the data itself) get outside of the available RAM space
performance gets hit fast since any sort of storage is a lot slower,
with spinning rust being excruciatingly slower since it has seek time
penalties that SSDs do not.

--
Karl Denninger
karl(at)denninger(dot)net <mailto:karl(at)denninger(dot)net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/