> 1.not sure if secondary index creation is the same as index rebuild
Fairly sure they are the same.
> 2.we noticed that the memory table flush looks still working,not the same
> as CASSANDRA-12796 mentioned,but the compactionExecutor pending is
Do you by chance have concurrent_compactors only set to 2? Seems like your
index builds are blocking other compactions from taking place.
Seems that maybe postflush is backed up because it's blocked on writes
generated from the rebuild? Maybe, anyway.
> 3.I'm wondering if the block only blocks the specified table which is
> creating secondary index?
If all your flush writers/post flushers are blocked I assume no other
flushes will be able to take place, regardless of table.
Seems like CASSANDRA-12796
<https://issues.apache.org/jira/browse/CASSANDRA-12796> is related but not
sure why it didn't get fixed in 2.1.