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From "Alex Petrov (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-12956) CL is not replayed on custom 2i exception
Date Thu, 01 Dec 2016 20:14:58 GMT


Alex Petrov commented on CASSANDRA-12956:

Thanks for the review!

I was also skeptical about two threads waiting for one another. Also, tried the approach you've
I hesitated mostly because it'd be blocking the flush thread (although you're right that it's
going to be
waiting for flushes anyways) and because {{flushMemtable}} is called from loop, so I wasn't
sure if it's
a good place.

In retrospect, I think your suggestion is much better than the previous version. I've re-implemented
a patch
for 3.0 as well, it got much simpler. Now, we do 2i flush before memtable flush during flush
of "data" memtable
(first one). We could bring back changes that expose sstable writer and run 2i flush on the
thread and commit sstable only on successful 2i flush, although since all cf memtables are
flushed sequentially
anyways and it might be a bit out of scope of the bugfix I decided to leave it this way. Simply
running 2i
flush in a different thread is not enough, as we need to ensure it's in sync with "data" memtable

Order of 2i/memtable flush does not matter, as for 2i it's only important that data is present
either in
sstable or in memtable. We can have the following situations: flush running (memtable is queried),
successfull (sstable is queried), flush unsuccessful (memtable is queried), flush unsuccessful
+ node restarted
(CL will replay the data and it'll be available from memtable again). So 3.0 patch relies
on this behaviour.


> CL is not replayed on custom 2i exception
> -----------------------------------------
>                 Key: CASSANDRA-12956
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Alex Petrov
>            Assignee: Alex Petrov
>            Priority: Critical
> If during the node shutdown / drain the custom (non-cf) 2i throws an exception, CommitLog
will get correctly preserved (segments won't get discarded because segment tracking is correct).

> However, when it gets replayed on node startup,  we're making a decision whether or not
to replay the commit log. CL segment starts getting replayed, since there are non-discarded
segments and during this process we're checking whether there every [individual mutation|]
in commit log is already committed or no. Information about the sstables is taken from [live
sstables on disk|].

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