Hi Koert, You should be able to see if it requires scanning the whole data by "explain" the query. The physical plan should say something about it. I wonder if you are trying the distinct-sort-by-limit approach or the max-date approach?
Best Regards, Jerry On Sun, Nov 1, 2015 at 4:25 PM, Koert Kuipers <ko...@tresata.com> wrote: > it seems pretty fast, but if i have 2 partitions and 10mm records i do > have to dedupe (distinct) 10mm records > > a direct way to just find out what the 2 partitions are would be much > faster. spark knows it, but its not exposed. > > On Sun, Nov 1, 2015 at 4:08 PM, Koert Kuipers <ko...@tresata.com> wrote: > >> it seems to work but i am not sure if its not scanning the whole dataset. >> let me dig into tasks a a bit >> >> On Sun, Nov 1, 2015 at 3:18 PM, Jerry Lam <chiling...@gmail.com> wrote: >> >>> Hi Koert, >>> >>> If the partitioned table is implemented properly, I would think "select >>> distinct(date) as dt from table order by dt DESC limit 1" would return the >>> latest dates without scanning the whole dataset. I haven't try it that >>> myself. It would be great if you can report back if this actually works or >>> not. :) >>> >>> Best Regards, >>> >>> Jerry >>> >>> >>> On Sun, Nov 1, 2015 at 3:03 PM, Koert Kuipers <ko...@tresata.com> wrote: >>> >>>> hello all, >>>> i am trying to get familiar with spark sql partitioning support. >>>> >>>> my data is partitioned by date, so like this: >>>> data/date=2015-01-01 >>>> data/date=2015-01-02 >>>> data/date=2015-01-03 >>>> ... >>>> >>>> lets say i would like a batch process to read data for the latest date >>>> only. how do i proceed? >>>> generally the latest date will be yesterday, but it could be a day >>>> older or maybe 2. >>>> >>>> i understand that i will have to do something like: >>>> df.filter(df("date") === some_date_string_here) >>>> >>>> however i do now know what some_date_string_here should be. i would >>>> like to inspect the available dates and pick the latest. is there an >>>> efficient way to find out what the available partitions are? >>>> >>>> thanks! koert >>>> >>>> >>>> >>> >> >