Choosing a database backend

Note

Ceilometer’s native database capabilities is intended for post processing and auditing purposes where responsiveness is not a requirement. It captures the full fidelity of each datapoint and thus is not designed for low latency use cases. For more responsive use cases, it’s recommended to store data in an alternative source such as Gnocchi. Please see Moving from Ceilometer to Gnocchi to find more information.

Note

As of Liberty, alarming support, and subsequently its database, is handled by Aodh.

Selecting a database backend for Ceilometer should not be done lightly for numerous reasons:

1. Not all backend drivers are equally implemented and tested. To help you make your choice, the table below will give you some idea of the status of each of the drivers available in trunk. Note that we do welcome patches to improve completeness and quality of drivers.
2. It may not be a good idea to use the same host as another database as Ceilometer can generate a LOT OF WRITES. For this reason it is generally recommended, if the deployment is targeting going into production, to use a dedicated host, or at least a VM which will be migratable to another physical host if needed. The following spreadsheet can help you get an idea of the volumes that ceilometer can generate: Google spreadsheet
3. If you are relying on this backend to bill customers, you will note that your capacity to generate revenue is very much linked to its reliability, which seems to be a factor dear to many managers.

The following is a table indicating the status of each database drivers:

Driver	API querying	API statistics
MongoDB	Yes	Yes
MySQL	Yes	Yes
PostgreSQL	Yes	Yes
HBase	Yes	Yes, except groupby & selectable aggregates

Moving from Ceilometer to Gnocchi

Gnocchi represents a fundamental change in how data is represented and stored. Installation and configuration can be found in Installing Manually. Differences between APIs can be found here.

There currently exists no migration tool between the services. To transition to Gnocchi, multiple dispatchers can be enabled in the Collector to capture data in both the native Ceilometer database and Gnocchi. This will allow you to test Gnocchi and transition to it fully when comfortable. The following should be included in addition to the required configurations for each backend:

[DEFAULT]
meter_dispatchers=database
meter_dispatchers=gnocchi
event_dispatchers=gnocchi