ceilometer/releasenotes/notes/single-thread-pipelines-f9e6ac4b062747fe.yaml
gordon chung 5750fddf28 improve notification processing
this patches does multiple things:

- it ignores batching when pulling from main queue to maintain as
much ordering as possible. this avoids related messages split across
multiple batches and one batch starting much farther along than another

- it sets pipeline processing listeners to single thread. at this stage,
the pipeline queue contains less messages and therefore very likely,
thread1 and thread2 will grab related messages and race to set cache

- adds sorting to pipeline queue so if batching is enabled, we can
further ensure that messages are in order before processing.

- enables batching by default. (one thread per listener grabbing one
message at a time will be slow.)

- offers better batching for direct to db dispatcher as resources are
grouped

Change-Id: Iac5b552bae1e73f93cbfc830b1e83510b1aceb9e
2016-09-09 13:03:04 +00:00

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YAML

---
upgrade:
- Batching is enabled by default now when coordinated workers are enabled.
Depending on load, it is recommended to scale out the number of
`pipeline_processing_queues` to improve distribution. `batch_size` should
also be configured accordingly.
fixes:
- Fix to improve handling messages in environments heavily backed up.
Previously, notification handlers greedily grabbed messages from queues
which could cause ordering issues. A fix was applied to sequentially
process messages in a single thread to prevent ordering issues.