On Fri, Jul 8, 2016 at 9:49 AM, Robert Haas <robertmh...@gmail.com> wrote:
> On Thu, Jul 7, 2016 at 4:56 PM, Bill Moran <wmo...@potentialtech.com> wrote:
>> Always does a seq scan on Postgres 9.5.2. (Yes, I know we're
>> a patch behind, the upgrade is on the schedule) on
>> Ubuntu 14.
>> I would expect it to be possible, and significantly more
>> efficient to do an index scan for that query.
> [...]
> We're probably missing a few tricks on queries of this type. If the
> index-traversal machinery had a mechanism to skip quickly to the next
> distinct value, that could be used here: walk up the btree until you
> find a page that contains keyspace not equal to the current key, then
> walk back down until you find the first leaf page that contains such a
> value.  That would potentially let you step over large chunks of the
> index without actually examining all the leaf pages, which for a query
> like this seems like it could be a big win.

FWIW I messed around with prototyping this idea here:


I hope to return to that and some related ideas eventually as I learn
more about the relevant areas of the source code, if someone doesn't
beat me to it.

https://wiki.postgresql.org/wiki/Loose_indexscan shows a recursive CTE
that does the same thing at a higher level.

Thomas Munro

Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:

Reply via email to