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From "Dan Blum" <db...@bbn.com>
Subject Bug in either InMemoryMap or NativeMap
Date Fri, 19 Feb 2016 20:34:59 GMT
(Resend: I forgot to actually subscribe before sending originally.)

I noticed a difference in behavior between our cluster and our tests running
on MiniCluster: when multiple put() calls are made to a Mutation with the
same CF, CQ, and CV and no explicit timestamp, on a live cluster only the
last one is written, whereas in Mini all of them are.

Of course in most cases it wouldn't matter but if there is a Combiner set on
the column (which is the case I am dealing with) then it does.

I believe the difference in behavior is due to code in NativeMap._mutate and
InMemoryMap.DefaultMap.mutate. In the former if there are multiple
ColumnUpdates in a Mutation they all get written with the same mutationCount
value; I haven't looked at the C++ map code but I assume that this means
that entries with the same CF/CQ/CV/timestamp will overwrite each other. In
contrast, in DefaultMap multiple ColumnUpdates are stored with an
incrementing kvCount, so the keys will necessarily be distinct.

My main question is: which of these is the intended behavior? We'll
obviously need to change our code to work with NativeMap's current
implementation regardless (since we don't want to use the Java maps on a
live cluster), but it would be useful to know if that change is temporary or
permanent.

My secondary question is whether there is any trick to getting native maps
to work in MiniCluster, which would be very helpful for our testing. I
changed the configuration XML we use and I can see that it picks up the
change - server.Accumulo logs "tserver.memory.maps.native.enabled = true,"
but NativeMap never logs that it tries to load the library so the setting
seems to be dropped somewhere.


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