Re: [geomesa-users] Attribute Indexing

[Chris Eichelberger <cne1x@xxxxxxxx>]

Marcel,

Roughly in order that you asked...

1.  Yes, it is always possible to get the raw key-value pairs out of
Accumulo.  The easiest way is via the Accumulo shell:


http://accumulo.apache.org/1.6/accumulo_user_manual.html#_accumulo_shell

Login, and then scan the "_attr_idx" table with a command somewhat
similar to this:

  scan -t geomesa_attr_idx

2.  There is nothing particularly novel about the way GeoMesa stores
secondary attribute indexes in the "_attr_idx" table.  This is a
straight lexicographically-encoded-value storage.

3.  There are two parts to using secondary indexes effectively:
encoding and querying.  The best references are to the GeoMesa source
where these occur:

  encoding:
https://github.com/locationtech/geomesa/blob/master/geomesa-accumulo/geomesa-accumulo-datastore/src/main/scala/org/locationtech/geomesa/accumulo/data/tables/AttributeTable.scala

  querying:
https://github.com/locationtech/geomesa/blob/master/geomesa-accumulo/geomesa-accumulo-datastore/src/main/scala/org/locationtech/geomesa/accumulo/index/AttributeIdxStrategy.scala

Enjoy!

Sincerely,
  -- Chris
  

On Fri, 2015-10-09 at 11:27 +0200, Marcel wrote:
> Hello,
> 
> is there a possibility to get the complete "raw" key-value pair of a 
> table as it is saved (a sample would be enough)? I want to look in the 
> "_attr_idx" table and understand how the index is built, e.g. when 
> indexing additional attributes like another Date, an Integer or a 
> String. Is it this a special or a common strategy (adapted for Accumulo) 
> for indexing? What fields available in the Accumulo table dsign did you 
> use (RowId, ColumnFamily, etc.)?
> 
> Thanks,
> Marcel Jacob.
> 
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