Re: Kernel cache vs shared_buffers

["Harald Armin Massa" <haraldarminmassa(at)gmail(dot)com>]

Heikki,


> > PostgreSQL on Windows. My current rule of thumb on Windows: set
> > shared_buffers to minimum * 2
> > Adjust effective_cache_size to the number given as "system cache"
> > within the task manager.
>
> Why?

I tried with shared_buffers = 50% of available memory, and with 30% of
available memory, and the thoughput on complex queries stalled or got
worse.

I lowered shared_buffers to minimum, and started raising
effective_cache_size, and performance on real world queries improved.
pg_bench did not fully agree when simulating large numbers concurrent
queries.

So I tried setting shared_buffers between minimum and 2.5*minimum, and
pg_bench speeds recovered and real world queries did similiar.

My understanding is that shared_buffers are realised as memory mapped
file in win32; and that they are only usually kept in memory. Maybe I
understood that wrong.

Harald

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