Thank you, Ashutosh. That's very informative. I appreciate that!
*Rossi* 2015-05-12 9:08 GMT+08:00 Ashutosh Chauhan <hashut...@apache.org>: > Hi Rossi, > > Historically, we used LoptOptimizeJoinRule of Calcite to do join > reordering. This does a greedy search on join order search space to find a > join order which is atleast as good as original join order of query. > Goodness being in term of estimated cost and not globally optimal because > of greedy nature of algorithm. > Our initial experimentation showed this rule was generating only left > leaning join tree, not considering bushy join orders, which made a huge > difference in query runtime especially because for star schema setups which > is common in analytical workloads, bushy joins usually are way better than > left (or right) leaning trees. At this point we added OptimizeBushyJoinRule. > > > However, a bit more experimentation and debugging informed us that > LoptOptimizeJoinRule > can actually generate bushy join trees. Problem was we had bugs in our > statistics/cost model which we were feeding to the rule. Once that was > established we switched back to LoptOptimizeJoinRule. > > So, in nut shell, hive CBO can and does generate bushy joins. If you have > test case where we are not generating bushy join, where we can, please post > back. Will be happy to take a look. > > Thanks, > Ashutosh > > > On Fri, May 8, 2015 at 11:57 AM, Ruoxi Sun <zanmato1...@gmail.com> wrote: > >> Hi all, >> >> I'm studying CBO code in hive. I have a question about bushy join >> optimization. >> >> Bushy join did get introduced in hive via HIVE-7577 >> <https://issues.apache.org/jira/browse/HIVE-7577>, and played an >> important role in optimizing several queries in TPCDS benchmark. Somehow I >> saw the bushy join rule was removed in HIVE-7687 >> <https://issues.apache.org/jira/browse/HIVE-7687>, and didn't find much >> comment about the removal. >> >> I wonder if the bushy join is totally gone from hive trunk? And if so, >> why is that? Or did I miss anything? >> >> Thanks in advance. >> >> *Rossi* >> > >
