Mars Hall created PIO-102:
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Summary: ESEngineInstances `getAll` results out of order
(Elasticsearch 5.x)
Key: PIO-102
URL: https://issues.apache.org/jira/browse/PIO-102
Project: PredictionIO
Issue Type: Bug
Components: Core
Affects Versions: 0.11.0-incubating
Reporter: Mars Hall
Assignee: Mars Hall
Using the new Elasticsearch 5.x REST storage client as the meta storage source
(`PIO_STORAGE_REPOSITORIES_METADATA_SOURCE=ELASTICSEARCH` setup in
conf/pio-env.sh), I found that once an engine has been trained a certain number
of times, that the most recent engine instance is no longer retrieved. So, I
tracked down where those Elasticsearch queries originate.
In the original Elasticsearch 1.x storage client, [the "scroll" pagination
responses are collected by
*appending*|https://github.com/apache/incubator-predictionio/blob/release/0.11.0/storage/elasticsearch1/src/main/scala/org/apache/predictionio/data/storage/elasticsearch/ESUtils.scala#L44]
them to one another.
In the new Elasticsearch 5.x client, [the "scroll" responses are collected by
*prepending*|https://github.com/apache/incubator-predictionio/blob/release/0.11.0/storage/elasticsearch/src/main/scala/org/apache/predictionio/data/storage/elasticsearch/ESUtils.scala#L152]
them to one another.
This out-of-order concatenation breaks [ESEngineInstances
`getLatestCompleted`|https://github.com/apache/incubator-predictionio/blob/release/0.11.0/storage/elasticsearch/src/main/scala/org/apache/predictionio/data/storage/elasticsearch/ESEngineInstances.scala#L192]
by erroneously replacing the head of the results with an older engine
instance, when there are enough engine instances to overflow a single page of
Elasticsearch hits.
I've observed this buggy behavior after ten trainings, when enough engine
instances are stored to trigger Elasticsearch's scroll feature.
I'll be opening a pull request shortly with the super-simple fix.
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