Hello Csaba Ringhofer, Impala Public Jenkins, I'd like you to reexamine a change. Please visit
http://gerrit.cloudera.org:8080/16000 to look at the new patch set (#6). Change subject: IMPALA-9632: Implement ds_hll_sketch() and ds_hll_estimate() ...................................................................... IMPALA-9632: Implement ds_hll_sketch() and ds_hll_estimate() These functions can be used to get cardinality estimates of data using HLL algorithm from Apache DataSketches. ds_hll_sketch() receives a dataset, e.g. a column from a table, and returns a serialized HLL sketch in string format. This can be written to a table or be fed directly to ds_hll_estimate() that returns the cardinality estimate for that sketch. Comparing to ndv() these functions bring more flexibility as once we fed data to the sketch it can be written to a table and next time we can save scanning through the dataset and simply return the estimate using the sketch. This doesn't come for free, however, as perfomance measurements show that ndv() is 2x-3.5x faster than sketching. On the other hand if we query the estimate from an existing sketch then the runtime is negligible. Another flexibility with these sketches is that they can be merged together so e.g. if we had saved a sketch for each of the partitions of a table then they can be combined with each other based on the query without touching the actual data. DataSketches HLL is sensitive for the order of the data fed to the sketch and as a result running these algorithms in Impala gets non-deterministic results within the error bounds of the algorithm. In terms of correctness DataSketches HLL is most of the time in 2% range from the correct result but there are occasional spikes where the difference is bigger but never goes out of the range of 5%. Even though the DataSketches HLL algorithm could be parameterized currently this implementation hard-codes these parameters and use HLL_4 and lg_k=12. For more details about Apache DataSketches' HLL implementation see: https://datasketches.apache.org/docs/HLL/HLL.html Testing: - Added some tests running estimates for small datasets where the amount of data is small enough to get the correct results. - Ran manual tests on TPCH25.lineitem to compare perfomance with ndv(). Depending on data characteristics ndv() appears 2x-3.5x faster. The lower the cardinality of the dataset the bigger the difference between the 2 algorithms is. - Ran manual tests on TPCH25.lineitem and functional_parquet.alltypes to compare correctness with ndv(). See results above. Change-Id: Ic602cb6eb2bfbeab37e5e4cba11fbf0ca40b03fe --- M be/src/codegen/impala-ir.cc M be/src/exprs/CMakeLists.txt M be/src/exprs/aggregate-functions-ir.cc M be/src/exprs/aggregate-functions.h A be/src/exprs/datasketches-functions-ir.cc A be/src/exprs/datasketches-functions.h M be/src/exprs/datasketches-test.cc M be/src/exprs/scalar-expr-evaluator.cc M common/function-registry/impala_functions.py M fe/src/main/java/org/apache/impala/catalog/BuiltinsDb.java A testdata/workloads/functional-query/queries/QueryTest/datasketches-hll.test A tests/query_test/test_datasketches.py 12 files changed, 452 insertions(+), 8 deletions(-) git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/00/16000/6 -- To view, visit http://gerrit.cloudera.org:8080/16000 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-Project: Impala-ASF Gerrit-Branch: master Gerrit-MessageType: newpatchset Gerrit-Change-Id: Ic602cb6eb2bfbeab37e5e4cba11fbf0ca40b03fe Gerrit-Change-Number: 16000 Gerrit-PatchSet: 6 Gerrit-Owner: Gabor Kaszab <gaborkas...@cloudera.com> Gerrit-Reviewer: Csaba Ringhofer <csringho...@cloudera.com> Gerrit-Reviewer: Gabor Kaszab <gaborkas...@cloudera.com> Gerrit-Reviewer: Impala Public Jenkins <impala-public-jenk...@cloudera.com>