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From James Taylor <jtay...@salesforce.com>
Subject Re: HBase Types: Explicit Null Support
Date Mon, 01 Apr 2013 23:49:10 GMT
On 04/01/2013 04:41 PM, Nick Dimiduk wrote:
> On Mon, Apr 1, 2013 at 4:31 PM, James Taylor <jtaylor@salesforce.com> wrote:
>>  From the SQL perspective, handling null is important.
>  From your perspective, it is critical to support NULLs, even at the expense
> of fixed-width encodings at all or supporting representation of a full
> range of values. That is, you'd rather be able to represent NULL than -2^31?
We've been able to get away with supporting NULL through the absence of 
the value rather than restricting the data range. We haven't had any 
push back on not allowing a fixed width nullable leading row key column. 
Since our variable length DECIMAL supports null and is a superset of the 
fixed width numeric types, users have a reasonable alternative.

I'd rather not restrict the range of values, since it doesn't seem like 
this would be necessary.
> On 04/01/2013 01:32 PM, Nick Dimiduk wrote:
>>> Thanks for the thoughtful response (and code!).
>>> I'm thinking I will press forward with a base implementation that does not
>>> support nulls. The idea is to provide an extensible set of interfaces, so
>>> I
>>> think this will not box us into a corner later. That is, a mirroring
>>> package could be implemented that supports null values and accepts
>>> the relevant trade-offs.
>>> Thanks,
>>> Nick
>>> On Mon, Apr 1, 2013 at 12:26 PM, Matt Corgan <mcorgan@hotpads.com> wrote:
>>>   I spent some time this weekend extracting bits of our serialization code
>>>> to
>>>> a public github repo at http://github.com/hotpads/**data-tools<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:
>>>> *
>>>> https://github.com/hotpads/**data-tools/blob/master/src/**
>>>> main/java/com/hotpads/data/**primitive/lists/LongArrayList.**java<https://github.com/hotpads/data-tools/blob/master/src/main/java/com/hotpads/data/primitive/lists/LongArrayList.java>
>>>> *
>>>> https://github.com/hotpads/**data-tools/blob/master/src/**
>>>> main/java/com/hotpads/data/**types/floats/DoubleByteTool.**java<https://github.com/hotpads/data-tools/blob/master/src/main/java/com/hotpads/data/types/floats/DoubleByteTool.java>
>>>> 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
>>>>>> 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
>>>>>> 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.
>>>>>> 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,
>>>>>> not
>>>>>> enough to simply encode null, it really needs to be encoded as 0x00
>>>>> as
>>>>> to sort lexicographically earlier than any other value.
>>>>>> What do you think? Any ideas, experiences, etc?
>>>>>> Thanks,
>>>>>> Nick

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