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 >
