Sounds good to me. Should we add a version field to the BLOOM_FILTER_UTF8 to deal with any future problems?
One other thought, in the protobuf definition I think it would be more efficient to have the bitset encoded as a byte[] to avoid the boxed long array. -dain > On Sep 8, 2016, at 3:42 PM, Owen O'Malley <omal...@apache.org> wrote: > > Dain, > That is a great point. I wasn't thinking about having to implement that > in C++, where it would really suck. (It was hard enough dealing with the > timezones in C++, so I should know better!) I got the approach from this > morning working and pushed it as a branch > https://github.com/omalley/orc/commit/38752621863bf8dc1f05a6e7d34552969395e5f5 > . > > The heaviest hammer would be to just create a new file version, but that > seems like overkill for this. (Although sooner or later we will get there, > since we need new encodings for decimal.) > > Ok, so how about: > > 1. We create a new stream kind (BLOOM_FILTER_UTF8) that always has UTF-8 > based bloom filters. It will be used for strings, chars, varchars, and > decimal. (Hopefully all charsets use the same bytes for ascii characters, > but I don't want to find the strange exceptions.) > > 2. We create a new config knob that let's you write both BLOOM_FILTER and > BLOOM_FILTER_UTF8 for users while they are transitioning. > > 3. The reader prefers BLOOM_FILTER_UTF8, but will fall back to BLOOM_FILTER > if it is an old file. > > Thoughts? > > .. Owen > > On Thu, Sep 8, 2016 at 11:02 AM, Dain Sundstrom <d...@iq80.com> wrote: > >>> On Sep 8, 2016, at 9:59 AM, Owen O'Malley <omal...@apache.org> wrote: >>> >>> Ok, Prasanth found a problem with my proposed approach. In particular, >> the >>> old readers would misinterpret bloom filters from new files. Therefore, >> I'd >>> like to propose a more complicated solution: >>> 1. We extend the stripe footer or bloom filter index to record the >> default >>> encoding when we are writing a string or decimal bloom filter. >>> 2. When reading a bloom filter, we use the encoding if it is present. >> >> Does that mean that you always write with he platform encoding? This >> would make using bloom filters for read in other programming languages >> difficult because you would need to do a UTF_8 to some arbitrary character >> encoding. This will also make using these bloom filters in performance >> critical sections (join loops) computationally expensive as you have to do >> a transcode. >> >> Also, I think the spec need to be clarified. The spec does not state the >> character encoding of the bloom filters. I assumed it was UTF_8 to match >> the normal string column encoding. It looks like the spec does not >> document the meaning of "the version of the writer” and what workarounds >> are necessary (or operating assumptions have been made). Once we have >> that, we should document that old readers assume that the platform default >> charset is consistent for readers and writers. >> >> As and alternative, for new files we could add add a new stream ID, so the >> old readers skip them. >> >> -dain
