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

Scott Brunza scottso at sonalysts.com
Tue Mar 8 05:28:25 PST 2011

I've several systems with 8-24 GB of RAM running postgres and postgis.  I built postgres as a 64-bit executable to take advantage of the larger address space.  As a rule for databases, they are memory hungry.  I generally follow:  effective cache size, 50% RAM; shared_buffers, 25% RAM.  There are other PG tuning parameters available in performance docs/discussions on the web.

With only 2GB of RAM, the bit-width of postgres shouldn't matter, and your setting of 1.5 GB shmmax seems a little too large.  Try keeping it below 1.25 GB, or even 1 GB.  Since you said this is only a prototype, performance shouldn't be a top priority.  You also don't want to starve the OS of resources.  Consider starting with your postgres setting half or even a quarter of what I stated above.  Also, consider lowering the max_connections setting; each connection requires more shared memory.  This way you can also limit the size of your kernel resources.

You can also dynamically change the kernel parameters with `sysctl -w PARAMETER=VALUE` from the command line to find a setting you're comfortable with before committing it to /etc/sysctl.conf.  The only reason to have large memory space for postgres is to store as much of the database as possible in memory, i.e., faster access and less/no swapping.

As for the pgAdmin question, it's a good tool, but it ultimately comes down to what you're comfortable with.  I prefer the command line.

Hope that clears things up at least a bit.

--- Let us all bask in television's warm glowing warming glow ---
Scott Brunza           860.326.3637         scottso at sonalysts.com

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