The multithreading effort is still ongoing. Joins, in particular, are not executed with multiple threads yet.
Not sure if I completely followed your last two questions, please correct me if I misunderstood. The general idea of the multithreading effort is to start multiple fragment instances per host. A fragment instance may contain an exchange node. On Wed, Oct 25, 2017 at 7:22 PM, 俊杰陈 <cjjnj...@gmail.com> wrote: > Thanks for the reply. > > I saw IMPALA-3902 <https://issues.apache.org/jira/browse/IMPALA-3902> > seems > to add support for multithread execution. It describes the goal is to > support running multiple fragment instances on a single node, is that means > coordinator generate multiple instances for a plan fragment on a single > node so that starts multiple exchange nodes to receive data and process? Or > it starts instances for different plan fragments for preparing > the streaming? > > 2017-10-25 22:08 GMT+08:00 Jeszy <jes...@gmail.com>: > > > Hello JJ, > > > > No, currently Impala uses one thread to execute the join (without > > regard for the amount of partitions that fit into memory). > > > > HTH > > > > On 25 October 2017 at 05:44, 俊杰陈 <cjjnj...@gmail.com> wrote: > > > Hi > > > > > > When Impala does a partitioned join on a node, it split the build input > > > into partitions until a partition can fit into memory and consume the > > probe > > > input then do the join and output rows. > > > > > > My question is will impala schedule multiple tasks to do join if > multiple > > > partitions fit into memory, or iterate over partitions? And for one > > > partition does it use multiple threads to do join? Thanks in advanced. > > > > > > > > > JJ > > > > > > -- > Thanks & Best Regards >
