Can someone explain working of multiple sessions used by Fastload/Multiload/TPT/FastExport job ?
I understand that max no. of sessions by a job should not be greater than total no. of amps in the system.
Let say one particular FastExport job is using 10 sessions. Expected rows to be exported are 100
Then how does workload is shared between multiple sessions?
Does each session exports 10 rows?
In case one session is doing all the export processing then why remaining sessions are required?
FExp creates datablocks (you can see the number in output) and passes them to the next available session, in your case it's a small number of blocks (maybe only one), so the 1st session might handle all rows.
Multiple sessions are only usefull if you got a larger amount of data.
thanks for the response.
could you please tell me the working of fastload/multi load/ tpt job?
Also in case we are exporting 1million rows. Does 10 sessions exports data in parallel or sequential manner(as you mentioned one session creates data block & passes to next session) ? If it's sequential then how does it achieve faster performance?
passing a datablock to a session is much faster than exporting that block, so the 1st session is still working when the 2nd session gets the next block and so on...
There's an overview/comparison of the different load utilities in the Database Administration manual (I prefer the PDFs over the online version): http://www.info.teradata.com/HTMLPubs/DB_TTU_15_00
And you find all details how the different utilities work in their manuals, too.