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From "roman.drapeko@baesystems.com" <roman.drap...@baesystems.com>
Subject RE: RowID design and Hive push down
Date Mon, 14 Sep 2015 20:38:31 GMT
Hi Josh,

Thanks for response.

Well, I am not an expert in Accumulo (so looking for a clue how to implement so we avoid as
much as possible custom code) - I will try to extend my answer a little bit and explain what
I don't understand.

For example, if my rowID looks like this: 20060101_blabla

I can query Hive something like that: select * from tbl where rowid > '20060101' and rowid
< '20060102', to my understanding what's happening under the hood is AccumuloPredicateHandler
 creates a Range('20060101', '20060102') that used for scanning (?)

Am I correct in saying that AccumuloPredicateHandler always creates a range that works with
strings only and it's not possible to amend this logic?

Regarding java primitives - it always can be represented as byte[4]

Roman



-----Original Message-----
From: Josh Elser [mailto:josh.elser@gmail.com]
Sent: 14 September 2015 21:10
To: user@accumulo.apache.org
Cc: Drapeko, Roman (UK Guildford)
Subject: Re: RowID design and Hive push down

I'm not positive what you mean by the "in-built RowID push down mechanism won't work with
unsigned bytes". Are you saying that you're trying to change your current rowID structure
to
unixTime+logicalSplit+hash structure? And you're trying to evaluate the
3 listed requirements against the new form?

First off, the Java primitives are signed, so you're going to be limited
by that. Don't forget that.

Have you seen accumulo.composite.rowid from
https://cwiki.apache.org/confluence/display/Hive/AccumuloIntegration.
Hypothetically, you can provide some logic which will do custom parsing
on your row and generate a struct from the components in your row ID.

Of interest might be:

https://github.com/apache/hive/blob/release-1.2.1/accumulo-handler/src/java/org/apache/hadoop/hive/accumulo/serde/AccumuloRowSerializer.java

https://github.com/apache/hive/blob/release-1.2.1/accumulo-handler/src/test/org/apache/hadoop/hive/accumulo/serde/TestAccumuloRowSerializer.java

You could extend the AccumuloRowSerializer to parse the bytes of the
rowId according to your own spec. I haven't explicitly tried this
myself, but in theory, I think your problems are meant to be solved by
this support. It will take a little bit of effort. Hive's LazyObject
type system is not my favorite framework to work with. Referencing some
of the HBaseStorageHandler code might also be worthwhile (as the two are
very similar).

- Josh

roman.drapeko@baesystems.com wrote:
> Hi there,
>
> Our current rowid format is yyyyMMdd_payload_sha256(raw data). It works
> nicely as we have a date and uniqueness guaranteed by hash, however
> unfortunately, rowid is around 50-60 bytes per record.
>
> Requirements are the following:
>
> 1)Support Hive on top of Accumulo for ad-hoc queries
>
> 2)Query original table by date range (e.g rowID < '20060101' AND rowID
>  >= '20060103') both in code and hive
>
> 3)Additional queries by ~20 different fields
>
> Requirement 3) requires secondary indexes and of course because each
> RowID is 50-60 bytes, they become super massive (99% of overall space)
> and really expensive to store.
>
> What we are looking to do is to reduce index size to a fixed size:
> {unixTime}{logicalSplit}{hash}, where unixTime is 4 bytes unsigned
> integer, logicalSplit - 2 bytes unsigned integer, and hash is 4 bytes -
> overall 10 bytes.
>
> What is unclear to me is how second requirement can be met in Hive as to
> my understanding an in-built RowID push down mechanism won't work with
> unsigned bytes?
>
> Regards,
>
> Roman
>
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