Re: low memory usage reported by 'top' indicates poor tuning?

Mark Stosberg wrote:
> Hello,
>
> I'm trying to make sense of the memory usage reported by 'top', compared
> to what "pg_database_size" shows. Here's one result:'

You are missing the most important parts of the equation:

1. What version of PostgreSQL.
2. What operating system -- scratch , I see freebsd
3. How big is your pg_dump in comparison to the pg_database_size()
4. What type of raid do you have?
5. What is your work_mem set to?
6. What about effective_cache_size?
7. Do you analyze? How often?

>
> select pg_size_pretty(pg_database_size('production'));
> pg_size_pretty
> ----------------
> 6573 MB
>
> Now, looking at memory use with "top", there is a lot memory that isn't
> being used on the system:
>
> Mem: 470M Active, 2064M Inact
>
> ( 3 Gigs RAM, total ).
>
> Overall performance is decent, so maybe there's no
> problem. However, I wonder if we've under-allocated memory to
> PostgreSQL. (This is a dedicated FreeBSD DB server).
>
> Some memory settings include:
>
> shared_buffers = 8192 (we have 450 connections)
> max_fsm_pages = 1250000 (we kept getting HINTs to bump it, so we did)
>
> Maybe we should be bumping up the "sort_mem" and "vacuum_mem" as well?
>
> I do sometimes see sorting and vacuuming as showing up as things I'd
> like to run faster.
>
> This list has been a great resource for performance tuning help, and I
> continue to appreciate your help. We've used PostgreSQL on every project
> we've had a choice on for the last 10 years. (Has it been that long?!)
> We've never regretted it once.
>
> Mark
>
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>

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