Frequently Asked Questions

I'm getting a Hector timeout on the queries, why?

Check the /var/log/cassandra/system.log and look for any errors. If you are doing a lot of deletes on your data you may see an error like this one:

ERROR [ReadStage:14] 2015-03-06 12:43:19,176 SliceQueryFilter.java (line 200) Scanned over 100000 tombstones in kairosdb.data_points; query aborted (see tombstone_failure_threshold).

One solution is to reduce your gc grace period as stated in this article: http://www.datastax.com/documentation/cassandra/2.0/cassandra/dml/dml_about_deletes_c.html

Why does the build for deb require X11?

Creating a debian package first builds an rpm and then uses alien to convert it to a deb. Alien requires the process to run as root so the build script will pop up a java dialog asking for the root password. You can get around this by passing the password on the build command like so

java make package-deb -D sudo=root_password

This will build the debian package without requiring X11

Why do I get duplicate data points?

Please reference this group conversation for additional context: https://groups.google.com/forum/#!topic/kairosdb-group/nWs84VO-SpY

KiaorsDB stores long and double data separately. If you don't specify the type of the data when inserting and you insert 10 and then insert 10.0 for the same name, tags and time you will get two data points. Kairos will interpret the first as a long and the second as a double.

How do I change the compaction strategy to TimeWindowCompactionStrategy TWCS?

Just like this:

alter table data_points with compaction = { 'class': 'TimeWindowCompactionStrategy', 'compaction_window_unit': 'HOURS', 'compaction_window_size': 24, 'timestamp_resolution': 'MILLISECONDS'};

alter table row_key_index with compaction = { 'class': 'TimeWindowCompactionStrategy', 'compaction_window_unit': 'HOURS', 'compaction_window_size': 24, 'timestamp_resolution': 'MILLISECONDS'};

Kairos stores data using millisecond time resolution so make sure to add that last bit or it gets confused.