Hi Burak,
Thanks for your quick reply. I guess what confuses me is that accumulator
won't be updated until an action is used due to the laziness, so
transformation such as a map won't even update the accumulator, then how
would restarted the transformation ended up updating accumulator more than
Hi Burak,
It makes sense, it boils down to any actions happens after transformations
then. Thanks for your answers.
Best,
Wei
2015-06-24 15:06 GMT-07:00 Burak Yavuz brk...@gmail.com:
Hi Wei,
During the action, all the transformations before it will occur in order
leading up to the action.
Hi Wei,
For example, when a straggler executor gets killed in the middle of a map
operation and it's task is restarted at a different instance, the
accumulator will be updated more than once.
Best,
Burak
On Wed, Jun 24, 2015 at 1:08 PM, Wei Zhou zhweisop...@gmail.com wrote:
Quoting from Spark
Hi Wei,
During the action, all the transformations before it will occur in order
leading up to the action. If you have an accumulator in any of these
transformations, then you won't get exactly once semantics, because the
transformation may be restarted elsewhere.
Bet,
Burak
On Wed, Jun 24,
Quoting from Spark Program guide:
For accumulator updates performed inside *actions only*, Spark guarantees
that each task’s update to the accumulator will only be applied once, i.e.
restarted tasks will not update the value. In transformations, users should
be aware of that each task’s update
