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Date: Thu, 18 Jul 2013 12:48:46 -0400
From: Josh Elser <josh.elser@gmail.com>
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To: user@accumulo.apache.org
Subject: Re: accumulo for a bi-map?
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Just be aware that if you have extremely wide matches (one record 
matching many other records), you've now forced these records to only 
ever be hosted on one tabletserver (as a row cannot be split across a 
tablet).

Given the size of what you outlined so far, you'd probably have to get 
up to the scale of tens of millions before this is a problem.

On 7/18/13 12:15 PM, Marc Reichman wrote:
> I have implemented an approach like Dave Marion's, where on a match
> during search I insert two rows:
>
> Row____
>
> 	
>
> Column Family____
>
> 	
>
> Column Qualifier____
>
> 	
>
> Value____
>
> 	
> 	
> 	
>
> abcd____
>
> 	
>
> ijkl____
>
> 	
>
> 90____
>
> 	
>
> __ __
>
> 	
> 	
> 	
>
> ijkl____
>
> 	
>
> abcd____
>
> 	
>
> 90____
>
> 	
>
> __ __
>
> __
>
> This works great for what I need to get, all abcd matches, all ijkl
> matches, specifically abcd->ijkl or reversed. For threshold filtering,
> I'm currently getting all of the results (from these cases) and then not
> retaining items below my threshold. I've looked at some ways to use a
> scan iterator to do this but I'm coming up short. Best idea I've had yet
> is to extend the ColumnQualifierFilter to see if I can do a "greater
> than" instead of an equals to accept or not. Any thoughts?
>
>
>
> On Wed, Jul 17, 2013 at 10:26 AM, Marc Reichman
> <mreichman@pixelforensics.com <mailto:mreichman@pixelforensics.com>> wrote:
>
>     Thank you all for your responses. Some follow-up thoughts/questions:
>
>     The use cases I'm chasing right now for retrieval are shaping up to be:
>     1. Get one ABCD->IJKL match score
>     2. Get all ABCD->* match scores
>     3. Either of the above, only greater than a specified threshold.
>
>     It's looking like the results may go into a different table than the
>     original features, so I can work a little more flexibly.
>
>     So far, Dave Marion's approach seems most closely suited to this,
>     but in a different table I wouldn't get the features back if I just
>     did a basic scan for the row key without other factors, which would
>     satisfy use case #2. I can satisfy case #1 easily if I make the
>     targets (IJKL) a qualifier and constrain by it on my scan as needed.
>
>     For #3, I'm a bit confused at a best way to do this. A simple
>     solution would be to just pull all the results from the #1/#2 cases
>     and filter out undesirables in my client-side code. Assuming
>     key:source, fam:target, col:score, is there some form of iterator or
>     filter I could use to process the column names and throw out what I
>     don't want with decent data locality for the processing?
>
>     Would it make any major impact if the scores were not integers but
>     doubles? I'm already anticipating having to parse doubles from the
>     scores as-stored in byte[] string form, but I don't know if the
>     performance impact would make any difference doing that locally
>     after or in an iterator.
>
>     I feel like this is close and I appreciate the guidance.
>
>     Thanks,
>     Marc
>
>
>     On Tue, Jul 16, 2013 at 6:25 PM, Josh Elser <josh.elser@gmail.com
>     <mailto:josh.elser@gmail.com>> wrote:
>
>         Instead of keeping all match scores inside of one Value, have
>         you considered thinking about your data in term of edges?
>
>         key:abcd->efgh score, value:88%
>         key:abcd->ijkl score, value:90%
>         key:efgh->abcd score, value:88%
>         key:ijkl->abcd score, value:90%
>
>         If you do go the route of storing both directions in Accumulo, a
>         structure like this will likely be much easier to maintain, as
>         you're not trying to manage difficult aggregation rules for
>         multiple updates to the matches for a single record.
>         Additionally, you should get really good compression (and even
>         better in 1.5) when you have large row prefixes (many matches
>         for abcd will equate to abcd being stored "once").
>
>         You could also store all of the features for a record in a key
>         which only has the record in the row.
>
>         key:abcd feature:foo1
>         key:abcd feature:foo2
>         etc.
>
>         Also, I'd encourage you to try to upgrade to 1.5.0 if you can,
>         but, if not, definitely update to 1.4.3 as it fixes a fair
>         number of bugs. It's as simple as stopping Accumulo, and copying
>         in the 1.4.3 Accumulo jar files to $ACCUMULO_HOME/lib, and
>         removing the 1.4.1 jars.
>
>         (apparently Dave Marion and I think alike)
>
>         - Josh
>
>
>         On 07/16/2013 05:28 PM, Marc Reichman wrote:
>
>             We are using accumulo as a mechanism to store feature data
>             (binary byte[]) for some simple keys which are used for a
>             search algorithm. We currently search by iterating over the
>             feature space using AccumuloRowInputFormat. Results come out
>             of a reducer into HDFS, currently in a SequenceFile.
>
>             A customer has asked if we can store our results somewhere
>             in our Hadoop infrastructure, and also perform nightly
>             searches of everything vs everything to keep match results
>             up to date.
>
>             To me, the storage of the results in alternate column
>             families (from the features) would be a way way to store the
>             matches alongside the key rows:
>             (key: abcd, features:{...}, matches{ 'm0: efgh-88%, 'm1':
>             ijkl-90%, ..., 'mN': etc }
>             (key: ijkl, features:{...}, matches{ 'm0: efgh-88%, 'm1':
>             abcd-90%, ..., 'mN': etc }
>
>             Match scores are equal between two items regardless of
>             perspective, so a->b is 90% as b->a is 90%.
>
>             Is there a way to simply add columns to an existing family
>             without having to name them or keep track of how many there
>             are? Am I better off making a column family for each match
>             key and then store score and other fields in columns? Making
>             one column with the key as the name and the score as the
>             value for each match under one family?
>
>             Ideally I would have some form of bidirectional map so I
>             could look at any key and find all the results as other
>             keys, and find any results to get other matches.
>
>             One approach is to simply add both sides of the relationship
>             every time anything matches anything else, which seems a bit
>             wasteful, space-wise.
>
>             Curious if any pre-existing ideas are out there. Currently
>             on hadoop 1.0.3/accumulo 1.4.1, not set in (hard) concrete.
>
>             Thanks,
>             Marc
>
>
>
>
>