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I found that the 2.2 has been in RC stage for almost two months and since it is already in RC 5 so our team decide to wait for it to be released to upgrade an existing cluster.
However it seems in the last couple of RCs there is always some additional issues that people want to fix before the release. When I check the wiki on http://spark.apache.org/versioning-policy.html, it says:
From Spark 2.0.0, in general, feature (“minor”) releases occur every 4 months. Hence, Spark 2.2.0 would generally be released about 4 months after 2.1.0. Maintenance releases happen as needed depending on need. A minor release usually sees 1-2 maintenance releases in the 6 months following its first release. Major releases do not happen according to a fixed schedule."
Spark used to have 3 releases per year since 1.0 but seems the pace has slowed down a little bit since 2.0. So does the 3 releases/year policy still hold generally?