We use PlayOrm to do something similar
We have an object like this(typing all this from memory)….
TimeSeries {
@NoSqlPartitionedByField
private long beginOfMonth;
@NoSqlIndexed
Private long timestamp;
}
Then we just use the ScalableSQL to query into the partition itself. This is
all on random partitioner as well. We could partition by day if we had way
more of a dataload, but we tend not to need that. The query looks something
like this "PARTITIONS s(:beginOfMonth) select s from TimeSeries as s"; OR
"PARTITIONS s(:beginOfMonth) select s from TimeSeries as s where s.time >
:start and s.time < :end"
Later,
Dean
From: Chin Ko <cko2...@gmail.com<mailto:cko2...@gmail.com>>
Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>"
<user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Date: Tuesday, December 11, 2012 7:23 AM
To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>"
<user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Subject: Selecting rows efficiently from a Cassandra CF containing time series
data
I would like to get some opinions on how to select an incremental range of rows
efficiently from a Cassandra CF containing time series data.
Background:
We have a web application that uses a Cassandra CF as logging storage. We
insert a row into the CF for every "event" of each user of the web application.
The row key is timestamp+userid. The column values are unstructured data. We
only insert rows but never update or delete any rows in the CF.
Data volume:
The CF grows by about 0.5 million rows per day. We have a 4 node cluster and
use the RandomPartitioner to spread the rows across the nodes.
Requirements:
There is a need to transfer the Cassandra data to another relational database
periodically. Due to the large size of the CF, instead of truncating the
relational table and reloading all rows into it each time, we plan to run a job
to select the "delta" rows since the last run and insert them into the
relational database.
We would like to have some flexibility in how often the data transfer job is
done. It may be run several times each day, or it may be not run at all on a
day.
Options considered:
- We are using RandomPartitioner, so range scan by row key is not feasible.
- Add a secondary index on the timestamp column, but reading rows via secondary
index still requires an equality condition and does not support range scan.
- Add a secondary index on a column containing the date and hour of the
timestamp. Iterate each hour between the time job was last run and now. Fetch
all rows of each hour.
I would appreciate any ideas of other design options of the Cassandra CF to
enable extracting the rows efficiently.
Besides Java, has anyone used any ETL tools to do this kind of delta extraction
from Cassandra?
Thanks,
Chin
