[postgis-users] Shared memory extesion on a a Mac for PostgreSQL/PostGIS

[Ture Pålsson]

2011/3/4 Rosemary Alles <rosemary.alles at gmail.com>:
> Hullo all,
>
> I'm attempting to store several sets of GPS derived spatial data (simple
> lat/lon mostly) in PostGIS and have hence installed PostgreSQL with the
> PostGIS extension on my iMac (running 10.6.6), the readme that comes with
> the PostgreSQL (at least for the latest version of it) casually warns of the
> need to increase -significantly- the amounts of shared memory availalbe for
> use. (See "attached" readme) Has anyone done this and what are the risks?

I played around with that a few months ago, and with my test case,
pulling an Openstreetmap extract of Sweden into the database on a 2
GByte iMac, I could not get any measurable performance improvement by
increasing Postgres's shared-memory parameters. It seems that the
OS-level buffer cache is doing a decent job. The obvious criticism
against this test case is that it has a single database "user"
executing a few large transactions which may not be a realistic
scenario. Then again, I don't think there are any major risks changing
the system coniguration as long as you stick to the recommended values
and always think twice before hitting "return".