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From "Dan Blum" <db...@bbn.com>
Subject RE: Bug in either InMemoryMap or NativeMap
Date Fri, 19 Feb 2016 22:59:22 GMT
We are already using logical time. I can definitely change to using multiple mutations or more
likely sum up the values myself and make a single put call.

 

From: Keith Turner [mailto:keith@deenlo.com] 
Sent: Friday, February 19, 2016 5:57 PM
To: user@accumulo.apache.org
Subject: Re: Bug in either InMemoryMap or NativeMap

 

 

 

On Fri, Feb 19, 2016 at 5:14 PM, Dan Blum <dblum@bbn.com> wrote:

Yes, please open an issue for this.

 

In the meantime, as a workaround is it safe to assign an arbitrary increasing timestamp when
calling Mutation.put()? That seems the simplest way to get the ColumnUpdates to be treated
properly.

 

Seems like that would work, but then you may have to keep track of the next timestamp across
processes.

A possible alternative is to configure the table to use logical time and multiple mutations.
 Logical time ensures every mutation is assigned a unique timestamp. The following program
is an example of this.

    String table = getUniqueNames(1)[0];
    Connector c = getConnector();
    c.tableOperations().create(table, 
        new NewTableConfiguration().setTimeType(TimeType.LOGICAL).withoutDefaultIterators());

    BatchWriterConfig config = new BatchWriterConfig();
    BatchWriter writer = c.createBatchWriter(table, config);

    Mutation m = new Mutation("row");
    m.put("cf1", "cq1", new Value("abc".getBytes()));
    writer.addMutation(m);
    m = new Mutation("row");
    m.put("cf1", "cq1", new Value("xyz".getBytes()));
    writer.addMutation(m);
    writer.close();

    Scanner scanner = c.createScanner(table, Authorizations.EMPTY);
    for (Entry<Key,Value> entry : scanner) {
      System.out.println(entry);
    }
  

This program prints 

  row cf1:cq1 [] 2 false=xyz
  row cf1:cq1 [] 1 false=abc

 

Accumulo assigned the timestamps 1 and 2.    In this case Accumulo will keep track of the
next timestamp for you.

 

If you do not use logical time, then the two mutations would likely get the same timestamp
because they arrived in the same millisecond. 

 

From: Keith Turner [mailto:keith@deenlo.com] 
Sent: Friday, February 19, 2016 5:11 PM
To: user@accumulo.apache.org
Cc: Jonathan Lasko; Maxwell Jordan; kstudzin@bbn.com
Subject: Re: Bug in either InMemoryMap or NativeMap

 

 

 

On Fri, Feb 19, 2016 at 3:34 PM, Dan Blum <dblum@bbn.com> wrote:

(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.

 

You made this issue easy to track down.

 

This seems like a bug w/ the native map.  The code allocates a unique int for each key/value
in the mutation.


https://github.com/apache/accumulo/blob/rel/1.6.5/server/tserver/src/main/java/org/apache/accumulo/tserver/InMemoryMap.java#L476
 

It seems like the native map code should increment like the DefaultMap code does.  Specifically
it seems like the following code should increment mutationCount (coordinating with the code
that calls it)

https://github.com/apache/accumulo/blob/rel/1.6.5/server/tserver/src/main/java/org/apache/accumulo/tserver/NativeMap.java#L532

 

Would you like to open an issue in Jira?

 


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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