Now that 8.3 is open, I was considering a revival of this old patch:
http://archives.postgresql.org/pgsql-hackers/2005-02/msg00832.php
I could probably clean it up with a little help from someone on this
list.
Advantages of this patch: If multiple seq scans are going in parallel on
the same table, it can drastically increase cache hit rate by
synchronizing the scans. In theory, it should also prevent the problem
where sequential scans can turn into random access from the disk.
Disadvantages:
* sequential scans no longer return results in a deterministic order. As
I understand it, this has effects on the regression tests and possibly a
few other locations in the code.
* While the in the use case, it should improve performance quite a lot.
However, the use case is quite narrow: you need to be running sequential
scans that are reading tuples from the same table at the same time. That
means the table can't fit into memory, but must be small enough that it
is sane to be executing multiple sequential scans on it in parallel.
Is there some interest in this patch? How would I go about proving
whether it's useful enough or not?
Regards,Jeff Davis