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From David Rosenstrauch <dar...@darose.net>
Subject Re: Reading ORC Files from S3
Date Tue, 29 Sep 2015 04:43:48 GMT
OK, well that was easy.  Figured out my issue and managed to get ORC 
working over s3a.  And got a huge speed-up over s3n!  (On the order of 10x!)

So yeah, I'm game for testing some new code when/if you're feeling 
motivated to work on this.  Feel free to email me off-list and we can 
get into the details.



On 09/28/2015 10:43 PM, David Rosenstrauch wrote:
> Super helpful response - thanks so much!  At least I know I'm not crazy
> now!  (And shouldn't spend any more time on tweaks trying to get this to
> work on s3n.)
> Let me try to start testing this using out-of-the-box s3a protocol.  (I
> haven't been able to get that to work at all yet - keep getting "Unable
> to load AWS credentials from any provider in the chain" errors.)  Once
> I'm able to get that far I'd be up for trying to test some new code. (As
> long as it doesn't wind up taking too much time.)
> Will report back soon.
> Thanks again!
> DR
> On 09/28/2015 06:14 PM, Gopal Vijayaraghavan wrote:
>>> avail.  I was hoping perhaps someone on the list here might
>>> be able to shed some light as to why we're having these problems and/or
>>> have some suggestions on how we might be able to work around them.
>> ...
>>>   (I.e., theoretically ORC should be able to skip reading large portions
>>> of the index files by jumping directly to the index
>>> records that match the supplied search criteria. (Or at least jumping to
>>> a stripe close to them.))  But this is proving not to be the case.
>> Not theoretically. ORC does that and that's the issue.
>> S3n is badly broken for a columnar format & even S3A is missing a couple
>> of features which are essential to get read performance over HTTP.
>> Here's one example - every seek() disconnects & restablishes an SSL
>> connection in S3 (that fix is a ~2x perf increase for S3a).
>> https://issues.apache.org/jira/browse/HADOOP-12444
>> In another scenario we found that a readFully(colOffset,... colSize) will
>> open an unbounded reader in S3n instead of reading the fixed chunk off
>> HTTP.
>> https://issues.apache.org/jira/browse/HADOOP-11867
>> The lack of this means that even the short-live keep-alive gets turned
>> off
>> by the S3 impl, when doing a forward-seek read pattern, because it is a
>> recv buffer-dropping disconnect, not a complete request.
>> The Amazon proprietary S3 drivers are not subject to these problems, so
>> they work with ORC very well. It's the open source S3 filesystem impls
>> which are holding us back.
>>> Is ORC simply unable to work efficiently against data stored on S3n?
>>> (I.e., due to network round-trips taking too long.)
>> S3n is unable to handle any columnar format efficiently - it fires an
>> GET for each seek, marked till end of the file. Any format which requires
>> forward seeks or bounded readers is going to die via TCP window &
>> round-trip thrashing.
>> I know what's needed for s3a to work well with columnar readers
>> (Parquet/ORC/RCFile included) and future proof it so that it will work
>> fine when HTTP/2 arrives.
>> If you're interested in being guinea pig for S3a fixes, it is currently
>> sitting on my back burner (I'm not a hadoop committer) - the FS fixes are
>> about two weeks worth of work for a single motivated dev.
>> Cheers,
>> Gopal

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