James Baker created CASSANDRA-15355:
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Summary: Schema push/pull race on continuous data changes
Key: CASSANDRA-15355
URL: https://issues.apache.org/jira/browse/CASSANDRA-15355
Project: Cassandra
Issue Type: Bug
Reporter: James Baker
In https://issues.apache.org/jira/browse/CASSANDRA-5025, pull based schema
updates were scheduled 1 minute after the schema change was first visible, so
as to prefer the push codepath as much as possible.
Unfortunately, this does not handle the case where there are many schema
changes happening - imagine a scenario where we create a table every 5 seconds
for 2 minutes - the first update tasks execute 60 seconds in and the schemas
may well be out of sync between nodes at that point.
In this case, there is some chance that when the task runs, the schemas are out
of sync because a subsequent schema update has occurred, and so the same
push/pull race has happened.
A fix is to modify the codepath such that the scheduled task is only run if the
other node's schema version is the same as when the task was scheduled. A
different (later scheduled) task should run otherwise.
For us, what we see is that when we have a reasonably large number of changes,
a few schema changes can have the unfortunate outcome of causing our nodes to
run out of memory and crash. This change stops that.
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