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From Josh Elser <>
Subject Re: OfflineScanner
Date Thu, 19 Feb 2015 15:27:03 GMT
Typically, if you're using the OfflineScanner, you'd clone the table you 
want to read and then take the clone offline. It's a simple (and fast) 
solution that doesn't interrupt the availability of the table.

Doing the read offline will definitely be faster (maybe 20%, I'm not 
entirely sure on accurate number and how it scales with nodes). The pain 
would be the extra work in creating the clone, offline'ing the table, 
and eventually deleting the clone when you're done with it. A little 
more work, but manageable.

Ara Ebrahimi wrote:
> Hi,
> I’m trying to optimize a connector we’ve written for Presto. In some cases we need
to perform full table scans. This happens across all the nodes but each node is assigned to
process only a sharded subset of data. Each shard is hosted by only 1 RFile. I’m looking
at the AbstractInputFormat and OfflineIterator and it seems like the code is not that hard
to use for this case. Is there any drawback? It seems like if the table is offline then OfflineIterator
is used which apparently reads the RFiles directly and doesn’t involve any RPC and I think
should be significantly faster. Is it so? Is there any drawback to using this while the table
is not offline but no other app is messing with the table?
> Thanks,
> Ara.
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