| Re: [geomesa-users] Attribute Indexing |
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Okay, so there is no special strategy for indexing a date?
I´m asking because there were different date formats I can imagine: 1) yyyy-MM-dd lexicographic sorting order: ... 2015-10-07 2015-10-08 2015-10-09 With this format it´s very efficient to query a date range because only one table scan is needed. 2) dd-MM-yyyy lexicographic sorting order: ... 07-10-2015 07-11-2015 07-12-2015 ... 08-10-2015 ... 09-10-2015 When querying for [07-10-2015 til 09-10-2015] we need multiple table scans and building an additional index would be less efficient. (But now we can efficiently ask for queries on a special day, e.g. 7th day. Although I believe this type of query is very rare.) So I will store my date in format 1). Please correct me if my thoughts are wrong. Thanks in advance, Marcel Jacob. > From: cne1x@xxxxxxxx > To: geomesa-users@xxxxxxxxxxxxxxxx > Date: Fri, 9 Oct 2015 07:23:57 -0400 > Subject: Re: [geomesa-users] Attribute Indexing > > 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. > > > > _______________________________________________ > > geomesa-users mailing list > > geomesa-users@xxxxxxxxxxxxxxxx > > To change your delivery options, retrieve your password, or unsubscribe from this list, visit > > http://www.locationtech.org/mailman/listinfo/geomesa-users > > > _______________________________________________ > geomesa-users mailing list > geomesa-users@xxxxxxxxxxxxxxxx > To change your delivery options, retrieve your password, or unsubscribe from this list, visit > http://www.locationtech.org/mailman/listinfo/geomesa-users |