Re: questions regarding shared_buffers behavior

> >
> > What is the procedure that postgres uses to decide whether or not a
> > table/index block will be left in the shared_buffers cache at the end
> > of the operation?
> >
>
> The only special cases are for sequential scans and VACUUM, which use continuously re-use a small section of the buffer cache in some cases instead.

Thanks - the part about sequential scans and the re-use of a small section of shared_buffers is the bit I was interested in.
I don't suppose you would be able to tell me how large that re-useable area might be?

Now, with regard to the behavior of table sequential scans: do the stat values in seq_scan and seq_tup_read reflect actual behavior.
I assume they do, but I'm just checking - these would be updated as the result of real I/O as opposed to fuzzy estimates?

Obviously, the reason I am asking this is that I am noticing high machine io levels that would only result from sequential scan activity.
The explain output says otherwise, but the seq_scan stat value for the table kinda correlates.
Hence my enquiry.

Thanks in advance.
Mr