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Eyal Allweil edited comment on DATAFU-117 at 5/9/16 8:50 AM: ------------------------------------------------------------- Ok, I opened a review board for it - It's at https://reviews.apache.org/r/46701/ I think all your previous comments are addressed there, except for the one about "this.set.add(o) && (this.set.size() == maxAmount". I don't think this can exceed the max size, because a single add operation can only increment the set's size by one, and the UDF is executed in a single thread. I ran a few tests comparing this UDF to a Pig nested foreach with DISTINCT followed by the builtin COUNT. On small inputs they perform about the same - even up to a million records - but if you have a situation with more skew (I checked 10 million records, with about 4 million distincts) then this UDF with a max value of say, 1,000,000, runs in a few minutes, and the nested foreach+distinct+count takes more than an hour - probably because it needs to keep all the distinct records in memory, rather than just reaching the desired threshold. was (Author: eyal): Ok, I opened a review board for it - can you see it? It's at https://reviews.apache.org/r/46701/ I think all your previous comments are addressed there, except for the one about "this.set.add(o) && (this.set.size() == maxAmount". I don't think this can exceed the max size, because a single add operation can only increment the set's size by one, and the UDF is executed in a single thread. I ran a few tests comparing this UDF to a Pig nested foreach with DISTINCT followed by the builtin COUNT. On small inputs they perform about the same - even up to a million records - but if you have a situation with more skew (I checked 10 million records, with about 4 million distincts) then this UDF with a max value of say, 10000, runs in about four minutes, and the nested foreach+distinct+count takes more than an hour - probably because it needs to keep all the distinct records in memory, rather than just reaching the desired threshold. > New UDF - CountDistinctUpTo > --------------------------- > > Key: DATAFU-117 > URL: https://issues.apache.org/jira/browse/DATAFU-117 > Project: DataFu > Issue Type: New Feature > Reporter: Eyal Allweil > Attachments: DATAFU-117-2.patch, DATAFU-117.patch > > > A UDF that counts distinct tuples within a bag, but only up to a preset > limit. If the bag contains more distinct tuples than the limit, the UDF > returns the limit. > This UDF can run reasonably well even on large bags if the limit chosen is > small enough though the count is done in memory. > We use this UDF in PayPal for filtering, when we don't need to use the actual > tuples afterward. -- This message was sent by Atlassian JIRA (v6.3.4#6332)