sql - What is Parallelism(Distribute Streams) in Execution plan -

what parallelism(distribute streams) operation in execution plan. why increasing rows count previous operation.

query :

select top 5000 mm.member_id,                 mm.member_no,                 mm.member_name,                 mm.trade_class,                 mt.description,                 ms.description,                 mai.address_1,                 mai.address_2,                 mai.city,                 mai.state,                 mai.zip   member_master mm        inner join member_type mt                on mt.code = mm.member_type        inner join member_status ms                on ms.code = mm.member_status        inner join member_address_info mai                on mm.member_id = mai.member_id  mai.primary_address_flag = 'yes' 

execution plan:

from above execution plan can see rows count increased 39,771 1,272,672. why happening?

the system has decided can benefit performing of processing in parallel. in case, it's apparently decided let 32 independent threads work set of rows (1272672 = 39771*32). shouldn't cause concern - - , "duplicate" rows eliminated later (gather streams) operation.