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v3.3.2-pre
Attendees: Brian, Danilo, Pere, Guilherme A, Jim P., Viktor, Zhe Z.
Danilo: About VecCore’s Vector’s I/O, tricking the I/O to see the vector as an array of double works for storage (tested with #ifdef in the user class). So the solution works, Xavi has a workaround and next we need to apply the same changed as we did for std::array to the VecCore’s vector.
Danilo: Streaming Column-wise std::array. I upload a couple of parts for the fix. FCC is testing the patch on their code and so far, so good. I expect a patch release next Monday.
Pere: However there was a failure this morning.
Danilo: Indeed, there was a missing cleanup that I upload a few minutes ago.
Viktor: I have been fixing some issues. I added support for multi-map and fixed problem in the template arguments parsing. Still having to deal with vector of pointer to base class, I have a solution that needs to be implemented. I am trying to do some benchmarking, I have a few example but would welcome more.
Philippe: Please look at tutorials/*/h1analysis*. We use this to demonstrate the look and feel of the various interfaces.
Danilo: I will send you some information.
Jim: I expect that the java version is likely to be 4 slower than the C++ version. In part because of caching effect, it will be hard to get a clear number/comparison with Sparks DataFrame.
Philippe: Can you disable caching?
Viktor: If you use RDD there is no caching.
Jim: I have been using the I/O part I described at the meeting. It is working great and building on it. Spending time on the distributed aspect of the project.
Philippe: I had discussion with Igor and Jin. I recommend to Igor to implement a class derived from TTree to allow analysis to use the nosql backend..
Jim: Indeed we have two avenue. One were with upload ROOT data into CouchDB and that’s what Igor is working on.
and I am doing the inverse having the client pull the information directly from ROOT files into FemtoCode. We are covering all cases with
Danilo: We are also working on adapting TDataFrame to read not only TTree data but also from other columnar file format.
Jim: Using TFile to access the NoSQL database would be extremely difficult due to the concept mismatch.
Philippe; Actually this is not the approach. Instead the idea is that rather than getting a TTree from a TFile, you could create a TTreeNoSQL based directly on the database information. See the TTreeSQL examples. There is a strong match between the TTree concept (cluster of entries, baskets) and the one you described.
Jim: meta data is custom … CouchDB does not (Want to) know anything about the content of the blob …
Zhe: I am implementing parallel (TTreeCache) unzip using TBB and working on making performance comparison with the older implementation.s
Biran: I am worried about the fine grained locking that might be a serialization bottleneck. So even it is faster, we may still want to improve this.
Danilo: You might benefit from using the TThreadExecutor.
Zhe: Thanks. I indeed already found it and I am using it :)
Zhe: About -fPIC and lz4, I saw that when adding -fPIC some unaligned memory routine. However when adding it to the official build, the difference.
Danilo: Removing fPIC seems like a non-starter. ROOT itself will require it.
Philippe: Could you investigate the differences in build in ROOT+fPIC vs regular build.
Brian: Did you try changing compiler version?
Zhe: I am using gcc 4.8
Brian: You should consider using Docker containers with gcc 6.
Brian: Do we have official docker containers?
Pere: No but we have all you need with CVMFS.
Danilo: Then we use Docker containers with CVMFS and it works fine.
Brian: Distracted with CHEP papers. I will ask DavidA for a written report.
Danilo: zfp a library for floating point compression. Did anybody look into this before?
Philippe: No, not really.