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From Les Hartzman <>
Subject Re: Wide rows/composite keys clarification needed
Date Mon, 21 Oct 2013 23:56:41 GMT
So I just saw a post about how Kundera translates all JPQL to CQL.

On Mon, Oct 21, 2013 at 4:45 PM, Jon Haddad <> wrote:

> If you're working with CQL, you don't need to worry about the column
> names, it's handled for you.
> If you specify multiple keys as part of the primary key, they become
> clustering keys and are mapped to the column names.  So if you have a
> sensor_id / time_stamp, all your sensor readings will be in the same row in
> the traditional cassandra sense, sorted by your time_stamp.
> On Oct 21, 2013, at 4:27 PM, Les Hartzman <> wrote:
> So looking at Patrick McFadin's data modeling videos I now know about
> using compound keys as a way of partitioning data on a by-day basis.
> My other questions probably go more to the storage engine itself. How do
> you refer to the columns in the wide row? What kind of names are assigned
> to the columns?
> Les
> On Oct 20, 2013 9:34 PM, "Les Hartzman" <> wrote:
>> Please correct me if I'm not describing this correctly. But if I am
>> collecting sensor data and have a table defined as follows:
>>          create table sensor_data (
>>                sensor_id int,
>>                time_stamp int,  // time to the hour granularity
>>                voltage float,
>>                amp float,
>>                PRIMARY KEY (sensor_id, time_stamp) ));
>> The partitioning value is the sensor_id and the rest of the PK components
>> become part of the column name for the additional fields, in this case
>> voltage and amp.
>> What goes into determining what additional data is inserted into this
>> row? The first time an insert takes place there will be one entry for all
>> of the fields. Is there anything besides the sensor_id that is used to
>> determine that the subsequent insertions for that sensor will go into the
>> same row as opposed to starting a new row?
>> Base on something I read (but can't currently find again), I thought that
>> as long as all of the elements of the PK remain the same (same sensor_id
>> and still within the same hour as the first reading), that the next
>> insertion would be tacked onto the end of the first row. Is this correct?
>> For subsequent entries into the same row for additional voltage/amp
>> readings, what are the names of the columns for these readings? My
>> understanding is that the column name becomes a concatenation of the
>> non-row key field names plus the data field names.So if the first go-around
>> you have <time_stamp>:<voltage> and <time_stamp>:<amp>, what
do the
>> subsequent column names become?
>> Thanks.
>> Les

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