(2011/11/28 20:50), Shigeru Hanada wrote: > (2011/11/25 17:27), Etsuro Fujita wrote: >> So, I think it might be better to estimate >> such costs by pgsql_fdw itself without EXPLAINing on the assumption that >> a remote postgres server has the same abilities for query optimization, >> which is less costly and widely applicable to the other DBMSs, while it, >> of course, only works once we have statistics and/or index information >> for foreign tables. But AFAIK we eventually want to have those, so I'd >> like to propose to use the proposed approach until that time. > > Knowledge of foreign indexes also provide information of sort order. > Planner will be able to consider merge join without local sort with such > information. Without foreign index, we have to enumerate possible sort > keys with Blute-Force approach for same result, as mentioned by > Itagaki-san before.
Yes, with the knowledge of foreign indexes, I think we can take the approach of thinking multiple plans for a foreign table; the cheapest unordered plan and the cheapest plan with a given sort order. In addition, it would be also possible to support nestloop-with-inner-foreign-indexscans on a foreign table as pointed out as future work by Tom Lane at PGCon 2011[1]. [1] http://www.pgcon.org/2011/schedule/attachments/188_Planner%20talk.pdf Best regards, Etsuro Fujita -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
