Re. Ty ty for your answer.
I'm using Tez as execution engine for this query. And it launches a job to yarn. Do you know why it launches a job just for a select when I use Tez as execution engine ? BR. Tale On Mon, Mar 21, 2016 at 4:17 PM, Mich Talebzadeh <mich.talebza...@gmail.com> wrote: > Hi, > > Your query is a table level query that covers all rows in the table. > > Using ODBC you are connecting to Hive server 2 that runs on a given port. > > Depending on the version of Hive you are running Hive under the bonnet is > most likely using Map-Reduce as the execution engine. > > Data has to be collected from all blocks that hold data for this table. > The underlying ORC stats can only act at table level as there is no > predicate push down and data has to be sent to ODBC driver through the > network. > > The ODBC driver can only communicate with Hive server 2 so there is no > connectivity to individual nodes from your client. > > So in summary Hive server 2 collects data from all blocks and forwards it > to the client. The actual collection and filtering of result set in SQL > query will depend on many factors. > > HTH > > Dr Mich Talebzadeh > > > > LinkedIn * > https://www.linkedin.com/profile/view?id=AAEAAAAWh2gBxianrbJd6zP6AcPCCdOABUrV8Pw > <https://www.linkedin.com/profile/view?id=AAEAAAAWh2gBxianrbJd6zP6AcPCCdOABUrV8Pw>* > > > > http://talebzadehmich.wordpress.com > > > > On 21 March 2016 at 14:26, Tale Firefly <tale.h...@gmail.com> wrote: > >> Hello guys ! >> >> I'm trying to understand the mechanism for a simple query select * from >> my_table when using HiveServer2. >> >> I'm using the hortonworks ODBC Driver for HiveServer2. >> I just do a select * from my_table. >> my_table is an ORC table based on files divised into blocks located on >> all my datanodes. >> I have 50 datanodes. >> >> My question is the following : >> Does all the data go from the datanodes to the node hosting the >> hiveserver2 before coming back to my client ? >> Or does all the data go directly from the datanodes to my client ? >> >> Hope you can help me o/ >> >> Thank you >> >> Tale >> > >
