Adam: do you want to schedule a hangout? On Tue, Dec 8, 2015 at 4:59 AM, Adam Gilmore <dragoncu...@gmail.com> wrote:
> That makes sense, yep. The problem is I guess with my implementation. I > will iterate through all Parquet files and try to eliminate ones where the > filter conflicts with the statistics. In instances where no files match > the filter, I end up with an empty set of files for the Parquet scan to > iterate through. I suppose I could just pick the schema of the first file > or something, but that seems like a pretty messy rule. > > Julien - I'd be happy to have a chat about this. I've pretty much got the > implementation down, but need to solve a few of these little issues. > > > On Fri, Dec 4, 2015 at 5:22 AM, Hanifi GUNES <hanifigu...@gmail.com> > wrote: > > > Regarding your point #1. I guess Daniel struggled with this limitation > as > > well. I merged few of his patches which addressed empty batch(no data) > > handling in various places during execution. That said, however, we still > > could not have time to develop a solid way to handle empty batches with > no > > schema. > > > > *- Scan batches don't allow empty batches. This means if a > > particular filter filters out *all* rows, we get an exception.* > > Looks to me, you are referring to no data rather than no schema here. I > > would expect graceful execution in this case. Do you mind sharing a > simple > > reproduction? > > > > > > -Hanifi > > > > 2015-12-03 10:56 GMT-08:00 Julien Le Dem <jul...@dremio.com>: > > > > > Hey Adam, > > > If you have questions about the Parquet side of things, I'm happy to > > chat. > > > Julien > > > > > > On Tue, Dec 1, 2015 at 10:20 PM, Parth Chandra <par...@apache.org> > > wrote: > > > > > > > Parquet metadata has the rowCount for every rowGroup which is also > the > > > > value count for every column in the rowGroup. Isn't that what you > need? > > > > > > > > On Tue, Dec 1, 2015 at 10:10 PM, Adam Gilmore <dragoncu...@gmail.com > > > > > > wrote: > > > > > > > > > Hi guys, > > > > > > > > > > I'm trying to (re)implement pushdown filtering for Parquet with the > > new > > > > > Parquet metadata caching implementation. > > > > > > > > > > I've run into a couple of challenges: > > > > > > > > > > 1. Scan batches don't allow empty batches. This means if a > > > particular > > > > > filter filters out *all* rows, we get an exception. I haven't > > read > > > > the > > > > > full comments on the relevant JIRA items, but it seems odd that > we > > > > can't > > > > > query an empty JSON file, for example. This is a bit of a > blocker > > > to > > > > > implement the pushdown filtering properly. > > > > > 2. The Parquet metadata doesn't include all the relevant > metadata. > > > > > Specifically, count of values is not included, therefore the > > default > > > > > Parquet statistics filter has issues because it compares the > count > > > of > > > > > values with count of nulls to work out if it can drop it. This > > > isn't > > > > > necessarily a blocker, but it feels ugly simulating there's "1" > > row > > > > in a > > > > > block (just to get around the null comparison). > > > > > > > > > > Also, it feels a bit ugly rehydrating the standard Parquet metadata > > > > objects > > > > > manually. I'm not sure I understand why we created our own objects > > for > > > > the > > > > > Parquet metadata as opposed to simply writing a custom serializer > for > > > > those > > > > > objects which we store. > > > > > > > > > > Thoughts would be great - I'd love to get a patch out for this. > > > > > > > > > > > > > > > > > > > > > -- > > > Julien > > > > > > -- Julien
