On Fri, Oct 23, 2015 at 4:41 PM, Amit Kapila <
amit.kapila16@gmail.com> wrote:
>
> On Fri, Oct 23, 2015 at 10:33 AM, Robert Haas <
robertmhaas@gmail.com> wrote:
Please find the rebased partial seq scan patch attached with this
mail.
Robert suggested me off list that we should once try to see if we
can use Seq Scan node instead of introducing a new Partial Seq Scan
node. I have analyzed to see if we can use the SeqScan node (containing
parallel flag) instead of introducing new partial seq scan and found that
we primarily need to change most of the functions in nodeSeqScan.c to
have a parallel flag check and do something special for Partial Seq Scan
and apart from that we need special handling in function
ExecSupportsBackwardScan(). In general, I think we can make
SeqScan node parallel-aware by having some special paths without
introducing much complexity and that can save us code-duplication
between nodeSeqScan.c and nodePartialSeqScan.c. One thing that makes
me slightly uncomfortable with this approach is that for partial seq scan,
currently the plan looks like:
QUERY PLAN
--------------------------------------------------------------------------
Gather (cost=0.00..2588194.25 rows=9990667 width=4)
Number of Workers: 1
-> Partial Seq Scan on t1 (cost=0.00..89527.51 rows=9990667 width=4)
Filter: (c1 > 10000)
(4 rows)
Now instead of displaying Partial Seq Scan, if we just display Seq Scan,
then it might confuse user, so it is better to add some thing indicating
parallel node if we want to go this route.
Thoughts?
