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

 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.