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From Matt Corgan <mcor...@hotpads.com>
Subject Re: HBase Types: Explicit Null Support
Date Mon, 01 Apr 2013 19:26:56 GMT
I spent some time this weekend extracting bits of our serialization code to
a public github repo at http://github.com/hotpads/data-tools.
 Contributions are welcome - i'm sure we all have this stuff laying around.

You can see I've bumped into the NULL problem in a few places:

Looking back, I think my latest opinion on the topic is to reject
nullability as the rule since it can cause unexpected behavior and
confusion.  It's cleaner to provide a wrapper class (so both LongArrayList
plus NullableLongArrayList) that explicitly defines the behavior, and costs
a little more in performance.  If the user can't find a pre-made wrapper
class, it's not very difficult for each user to provide their own
interpretation of null and check for it themselves.

If you reject nullability, the question becomes what to do in situations
where you're implementing existing interfaces that accept nullable params.
 The LongArrayList above implements List<Long> which requires an add(Long)
method.  In the above implementation I chose to swap nulls with
Long.MIN_VALUE, however I'm now thinking it best to force the user to make
that swap and then throw IllegalArgumentException if they pass null.

On Mon, Apr 1, 2013 at 11:41 AM, Doug Meil <doug.meil@explorysmedical.com>wrote:

> HmmmÅ  good question.
> I think that fixed width support is important for a great many rowkey
> constructs cases, so I'd rather see something like losing MIN_VALUE and
> keeping fixed width.
> On 4/1/13 2:00 PM, "Nick Dimiduk" <ndimiduk@gmail.com> wrote:
> >Heya,
> >
> >Thinking about data types and serialization. I think null support is an
> >important characteristic for the serialized representations, especially
> >when considering the compound type. However, doing so in directly
> >incompatible with fixed-width representations for numerics. For instance,
> >if we want to have a fixed-width signed long stored on 8-bytes, where do
> >you put null? float and double types can cheat a little by folding
> >negative
> >and positive NaN's into a single representation (this isn't strictly
> >correct!), leaving a place to represent null. In the long example case,
> >the
> >obvious choice is to reduce MAX_VALUE or increase MIN_VALUE by one. This
> >will allocate an additional encoding which can be used for null. My
> >experience working with scientific data, however, makes me wince at the
> >idea.
> >
> >The variable-width encodings have it a little easier. There's already
> >enough going on that it's simpler to make room.
> >
> >Remember, the final goal is to support order-preserving serialization.
> >This
> >imposes some limitations on our encoding strategies. For instance, it's
> >not
> >enough to simply encode null, it really needs to be encoded as 0x00 so as
> >to sort lexicographically earlier than any other value.
> >
> >What do you think? Any ideas, experiences, etc?
> >
> >Thanks,
> >Nick

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