Grokbase Groups Hive dev April 2013
FAQ
Hiya Nick,
Pig converts data for HBase storage using this class:
https://svn.apache.org/repos/asf/pig/trunk/src/org/apache/pig/backend/hadoop/hbase/HBaseBinaryConverter.java(which
is mostly just calling into HBase's Bytes class). As long as Bytes
handles the null stuff, we'll just inherit the behavior.

On Tue, Apr 2, 2013 at 9:40 AM, Nick Dimiduk wrote:

I agree that a user-extensible interface is a required feature here.
Personally, I'd love to ship a set of standard GIS tools on HBase. Let's
keep in mind, though, that SQL and user applications are not the only
consumers of this interface. A big motivation is allowing interop with the
other higher MR languages. *cough* Where are my Pig and Hive peeps in this
thread?

On Mon, Apr 1, 2013 at 11:33 PM, James Taylor <jtaylor@salesforce.com
wrote:
Maybe if we can keep nullability separate from the
serialization/deserialization, we can come up with a solution that works?
We're able to essentially infer that a column is null based on its value
being missing or empty. So if an iterator through the row key bytes could
detect/indicate that, then an application could "infer" the value is null.
We're definitely planning on keeping byte[] accessors for use cases that
need it. I'm curious on the geographic data case, though, could you use a
fixed length long with a couple of new SQL built-ins to encode/decode the
latitude/longitude?

On 04/01/2013 11:29 PM, Jesse Yates wrote:

Actually, that isn't all that far-fetched of a format Matt - pretty
common
anytime anyone wants to do sortable lat/long (*cough* three letter
agencies
cough*).

Wouldn't we get the same by providing a simple set of libraries (ala
orderly + other HBase useful things) and then still give access to the
underlying byte array? Perhaps a nullable key type in that lib makes
sense
if lots of people need it and it would be nice to have standard
libraries
so tools could interop much more easily.
-------------------
Jesse Yates
@jesse_yates
jyates.github.com


On Mon, Apr 1, 2013 at 11:17 PM, Matt Corgan wrote:

Ah, I didn't even realize sql allowed null key parts. Maybe a goal of
the
interfaces should be to provide first-class support for custom user
types
in addition to the standard ones included. Part of the power of
hbase's
plain byte[] keys is that users can concoct the perfect key for their
data
type. For example, I have a lot of geographic data where I interleave
latitude/longitude bits into a sortable 64 bit value that would
probably
never be included in a standard library.


On Mon, Apr 1, 2013 at 8:38 PM, Enis Söztutar <enis.soz@gmail.com>
wrote:

I think having Int32, and NullableInt32 would support minimum
overhead,
as
well as allowing SQL semantics.


On Mon, Apr 1, 2013 at 7:26 PM, Nick Dimiduk <ndimiduk@gmail.com>
wrote:

Furthermore, is is more important to support null values than squeeze
all
representations into minimum size (4-bytes for int32, &c.)?
On Apr 1, 2013 4:41 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?
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
<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/**<
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/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<
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:
HmmmŠ 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" 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

Search Discussions

Discussion Posts

Previous

Follow ups

Related Discussions

Discussion Navigation
viewthread | post
posts ‹ prev | 2 of 3 | next ›
Discussion Overview
groupdev @
categorieshive, hadoop
postedApr 2, '13 at 4:41p
activeApr 5, '13 at 12:34a
posts3
users2
websitehive.apache.org

2 users in discussion

Nick Dimiduk: 2 posts Dmitriy Ryaboy: 1 post

People

Translate

site design / logo © 2021 Grokbase