Re: PG 8.3 and large shared buffer settings

On Fri, Sep 25, 2009 at 8:53 AM, Scott Carey <scott@richrelevance.com> wrote:
> That won't work well anyway because the postgres shared_buffers dos not cache
> things that are sequentially scanned (it uses a ring buffer for each scan).  So, for
> any data that is only accessed by sequential scan, you're relying on the OS and
> the disks.  If you access a table via index scan though, all its pages will go through
> shared_buffers.

Does it doe this even if the block was already in shared_buffers?
That seems like a serious no-no to me to read the same block into
different buffers.  I thought that the sequential scan would have to
break stride when it encountered a block already in buffer.  But I
haven't looked at the code, maybe I am over analogizing to other
software I'm familiar with.

Jeff