The admission controller test fetches multiple metrics relating to the
admission controller. Before this patch it fetched the whole metrics
list for each metric, meaning there was a substantial window for
the metrics to be inconsistent for a single backend. Now the metrics are
only fetched once. Metric updates are not transactional so there is
still a small window for raciness if an admission decision is made
exactly when the metrics are fetched.
Also try to detect the specific race between updating "dequeued"
and "admitted" that we saw in practice, since the race is still
possible with a smaller window. In that case we retry getting
the metrics.
Change-Id: I2f16edbec53e49446c4c37ef5f926eedb5604319
Reviewed-on: http://gerrit.cloudera.org:8080/10330
Reviewed-by: Tim Armstrong <tarmstrong@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
ab2fc5c8b8