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From Adam Fuchs <>
Subject Re: pre-sorting row keys vs not pre-sorting row keys
Date Thu, 29 Oct 2015 23:36:12 GMT
I bet what you're seeing is more efficient batching in the latter case.
BatchWriter goes through a binning phase whenever it fills up half of its
buffer, binning everything in the buffer into tablets. If you give it
sorted data it will probably be binning into a subset of the tablets
instead of all of them, which would be likely in the random case. Fewer
batches translates into fewer RPC calls, and less general overhead.

This generally indicates that if your data starts roughly partitioned it
will load faster, and that becomes more important as you scale up.


We just did a simple test:

- insert 10k batches of columns
- sort the same 10k batch based on row keys and insert

So basically the batch writer in the first test has items in non-sorted
order and in the second one in sorted order. We noticed 50% better
performance in the sorted version! Why is that the case? Is this something
we need to consider doing for live ingest scenarios?



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