Re: Oracle v. Postgres 9.0 query performance

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Tony Capobianco <tcapobianco@xxxxxxxxxxxxxx> wrote:
 
> According to some documentation, I want to set
> effective_cache_size to my OS disk cache + shared_buffers.
 
That seems reasonable, and is what has worked well for me.
 
> In this case, I have 4 quad-core processors with 512K cache (8G)
> and my shared_buffers is 7680M.  Therefore my effective_cache_size
> should be approximately 16G?
 
I didn't follow that at all.  Can you run `free` or `vmstat`?  If
so, go by what those say your cache size is.
 
> Most of our other etl processes are running fine, however I'm
> curious if I could see a significant performance boost by reducing
> the effective_cache_size.
 
Since it is an optimizer costing parameter and has no affect on
memory allocation, you can set it on a connection and run a query on
that connection to test the impact.  Why wonder about it when you
can easily test it?
 
-Kevin

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