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From Jonathan Coveney <jcove...@gmail.com>
Subject Re: Early projection and lazy casting
Date Sat, 03 Dec 2011 00:33:52 GMT
In what context? I always thought that it generally could, but that if you
do joins it doesn't. Would be curious to know more from someone who knows...

2011/12/2 Jie Li <jieli@cs.duke.edu>

> Hi all,
>
> We just figured out Pig 0.9.1 doesn't drop those non-necessary fields asap,
> which really affects the performance. Though
>
> http://ofps.oreilly.com/titles/9781449302641/load_and_store_funcs.html#loadfunc_loaderpushdownsaid
> that "As part of its optimizations Pig analyzes Pig Latin scripts and
> determines what fields in an input it needs at each step in the script. It
> uses this information to aggressively drop fields it no longer needs."
>
> We also found that Pig casts the data into the types defined in the schema,
> which is usually unnecessary, as most of them will be soon dropped.
>
> To work around these, we have to manually drop those fields and remove the
> types in the schema, which are really not interesting.
>
> Jie
>

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