Todd Lipcon has posted comments on this change. ( http://gerrit.cloudera.org:8080/9440 )
Change subject: KUDU-2312: Scan predicate application ordering is non-deterministic ...................................................................... Patch Set 4: I did a little research and it actually appears that Impala is ordering predicates based on selectivity. See https://gist.github.com/89344b31e455a72a831761b5c6ef75f7 That said, I checked a version of kudu without this patch and the scans dashboard shows that the predicates were being evaluated in the same order (field5 followed by field4) regardless of what Impala said in the explain. I also checked an RPC trace and can see that the actual RPC is showing the predicates in the order [field4, field5] regardless of what the explain plan says. So it seems like our client is likely dropping the order somewhere during the scan optimization phase. If we changed this to be a std::stable_sort instead of tie-breaking with index, would we end up retaining the client's predicate order, you think? or would it be a bigger change? Certainly seems like it would be valuable to take advantage of Impala's stats knowledge in our order of application. -- To view, visit http://gerrit.cloudera.org:8080/9440 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-Project: kudu Gerrit-Branch: master Gerrit-MessageType: comment Gerrit-Change-Id: I99b2cabecd8626cad7e11fbdd492af7276e08348 Gerrit-Change-Number: 9440 Gerrit-PatchSet: 4 Gerrit-Owner: Dan Burkert <danburk...@apache.org> Gerrit-Reviewer: Dan Burkert <danburk...@apache.org> Gerrit-Reviewer: Kudu Jenkins Gerrit-Reviewer: Thomas Tauber-Marshall <tmarsh...@cloudera.com> Gerrit-Reviewer: Tidy Bot Gerrit-Reviewer: Todd Lipcon <t...@apache.org> Gerrit-Comment-Date: Sat, 03 Mar 2018 01:52:37 +0000 Gerrit-HasComments: No
