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From Michael Moss <michael.m...@gmail.com>
Subject Accumulo: "BigTable" vs. "Document Model"
Date Fri, 04 Sep 2015 15:42:20 GMT
Hello, everyone.

I'd love to hear folks' input on using the "natural" data model of Accumulo
("BigTable" style) vs more of a Document Model. I'll try to succinctly
describe with a contrived example.

Let's say I have one domain object I'd like to model, "SensorReadings". A
single entry might look something like the following with 4 distinct CF, CQ
pairs.

RowKey: DeviceID-YYYMMDD-ReadingID (i.e. - 1-20150101-1234)
CF: "Meta", CQ: "Timestamp", Value: <Some timestamp>
CF: "Sensor", CQ: "Temperature", Value: 80.4
CF: "Sensor", CQ: "Humidity", Value: 40.2
CF: "Sensor", CQ: "Barometer", Value: 29.1

I might do queries like "get me all SensorReadings for 2015 for DeviceID =
1" and if I wanted to operate on each SensorReading as a single unit (and
not as the 4 'rows' it returns for each one), I'd either have to aggregate
the 4 CF, CQ pairs for each RowKey client side, or use something like the
WholeRowIterator.

In addition, if I wanted to write a query like, "for DeviceID = 1 in 2015,
return me SensorReadings where Temperature > 90, Humidity < 40, Barometer >
31", I'd again have to either use the WholeRowIterator to 'see' each entire
SensorReading in memory on the server for the compound query, or I could
take the intersection of the results of 3 parallel, independent queries on
the client side.

Where I am going with this is, what are the thoughts around creating a
Java, Protobuf, Avro (etc) object with these 4 CF, CQ pairs as fields and
storing each SensorReading as a single 'Document'?

RowKey: DeviceID-YYYMMDD
CF: ReadingID Value: Protobuf(Timestamp=123, Temperature=80.4,
Humidity=40.2, Barometer = 29.1)

This way you avoid having to use the WholeRowIterator and unless you often
have queries that only look at a tiny subset of your fields (let's say just
"Temperature"), the serialization costs seem similar since Value is just
bytes anyway.

Appreciate folks' experience and wisdom here. Hope this makes sense, happy
to clarify.

Best.

-Mike

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