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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+======================================
+Support Time To Live on Event Database
+======================================
+
+https://blueprints.launchpad.net/ceilometer/+spec/event-database-ttl
+
+
+Problem description
+===================
+
+Event database grows over time, after we dump data to larger storage system,
+the old data in event database should be cleared, but now, there is no such
+way to do it.
+
+Proposed change
+===============
+
+Add time to live feature on event database, just like what we do on metering
+database. A new option event_time_to_live will be added, such as what we do
+for metering database.
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+Security impact
+---------------
+
+None
+
+Pipeline impact
+---------------
+
+None
+
+Other end user impact
+---------------------
+
+User now can clean event database when they run ceilometer-expirer
+and set event_time_to_live options to value that larger than 0.
+
+Performance/Scalability Impacts
+-------------------------------
+
+Performance can be improved since event database can keep light.
+
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  aji-zqfan
+
+Other contributors:
+  Contributors who want to help on databases except MongoDB
+
+Ongoing maintainer:
+  aji-zqfan
+
+Work Items
+----------
+
+1. Implement it on MongoDB
+2. Implement it on other database back end
+
+
+Future lifecycle
+================
+
+None
+
+
+Dependencies
+============
+
+None
+
+
+Testing
+=======
+
+Unit test code will be added along with source code.
+
+
+Documentation Impact
+====================
+
+New option will be added, so OS Configuration Document should be update,
+and new feature is added, Administrator's Guide Document should be updated
+too. But not this spec's job.
+
+
+References
+==========
+
+None