When are the checksums for local files generated?

[Chris Mildebrandt <ch...@woodenrhino.com>]

Hello,

For the intermediate files the mapper generates (which will get sent to the
reducers), when are the checksums generated? Are they generated when a
request comes in for transfer, or are they generated when the file is
initially created? Also, are checksums checked/verified if the file is
accessed again by a local reducer (doesn't have to go over the network)?

Thanks,
-Chris