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From "Josh Elser (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-3602) BatchScanner optimization for AccumuloInputFormat
Date Wed, 25 Mar 2015 18:46:54 GMT


Josh Elser commented on ACCUMULO-3602:

bq. Alright, 1.7 target it is then. I'll rebase on master.

Cool. Thank you, and again, sorry for the pain semver is causing.

bq. Should it be the default approach when possible? I'm not sure, probably yes. Locality
would be tied to a tablet, which is hosted on one machine, you still can reap the benefits
of several IO threads. The effort on querying the TabletLocator is spent in either case, so
why not use it.

As long as the Split generation is still binning the ranges together on locality, I think
this would be fine for most cases. There's still the possibility that tablets move the mappers
read them, but that's nothing new.

One case I thought of is that a Mapper could have special logic based on the fact that it
will receive sorted Key-Value pairs which a BatchScanner-by-default would break. I'm not sure
how common this is nor if it's a big concern.

My cautious nature would be to say that it's safest to have 1.7 introduce configuration that
allow use of BatchScanners and then 2.0 could switch that to the default? A nice enum could
help make a setter which ensure API compat between 1.7 and 2.0 and let the default configuration
change underneath. Haven't thought it through completely, just a first reaction. [~kturner]
is really good at this stuff. Maybe he can weigh :)

> BatchScanner optimization for AccumuloInputFormat
> -------------------------------------------------
>                 Key: ACCUMULO-3602
>                 URL:
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: client
>    Affects Versions: 1.6.1, 1.6.2
>            Reporter: Eugene Cheipesh
>            Assignee: Eugene Cheipesh
>              Labels: performance
> Currently {{AccumuloInputFormat}} produces a split for reach {{Range}} specified in the
configuration. Some table indexing schemes, for instance z-order geospacial index, produce
large number of small ranges resulting in large number of splits. This is specifically a concern
when using {{AccumuloInputFormat}} as a source for Spark RDD where each Split is mapped to
an RDD partition.
> Large number of small RDD partitions leads to poor parallism on read and high overhead
on processing. A desirable alternative is to group ranges by tablet into a single split and
use {{BatchScanner}} to produce the records. Grouping by tablets is useful because it represents
Accumulos attempt to distributed stored records and can be influance by the user through table
> The grouping functionality already exists in the internal {{TabletLocator}} class. 
> Current proposal is to modify {{AbstractInputFormat}} such that it generates either {{RangeInputSplit}}
or {{MultiRangeInputSplit}} based on a new setting in {{InputConfigurator}}.  {{AccumuloInputFormat}}
would then be able to inspect the type of the split and instantiate an appropriate reader.
> The functinality of {{TabletLocator}} should be exposed as a public API in 1.7 as it
is useful for optimizations.

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