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From Stack <st...@duboce.net>
Subject Re: Problem with flushing and identical timestamps
Date Wed, 27 Jan 2010 00:48:55 GMT
Here's a bit more on the below:

When you say "...puts ³aaa², flushes, and quits", you mean quit your
client or stop/start hbase?

The getMap behavior seems off (Here's where you'd slot in
hbase-1485?).  I've added the below to hbase-1485 since it has nice


On Tue, Jan 26, 2010 at 9:36 AM, Rod Cope <rod.cope@openlogic.com> wrote:
> Hi,
> I¹m seeing behavior on 0.20.2 and 0.20.3 that doesn¹t seem quite right and
> would like to know if this is by design, a bug, or something I¹m doing
> wrong.
> Background:
> When I do a put that includes a timestamp like this (conceptually ­ I know
> this is not the actual API), it works just fine.
>  put ³table², ³family², ³column², ³bbb², 12345
> Then, if I do another put in the same client code using the same timestamp
> like this...
>  put ³table², ³family², ³column², ³aaa², 12345
> ...and I create a scanner, grab a Result, and iterate over all values using
> list(), I get this...
>  ³table², ³family², ³column², ³aaa², 12345
> So far, so good.  Now, if I truncate the table from the shell and run a new
> program that does a flush() on the table between the two put¹s, but does it
> in the same client program back-to-back, I also get the same results from
> list().
> -----
> Problem:
> Here¹s where the trouble starts.  I truncate the table and run a new program
> that puts ³bbb², flushes the table, and quits.  Here¹s what I get from
> list():
>  ³table², ³family², ³column², ³bbb², 12345
> Then I run another program that puts ³aaa², flushes, and quits.  Here¹s what
> I get from list():
>  ³table², ³family², ³column², ³aaa², 12345
>  ³table², ³family², ³column², ³bbb², 12345
> And if I then run a third program that puts ³ccc², flushes, and quits, I get
> this from list():
>  ³table², ³family², ³column², ³ccc², 12345
>  ³table², ³family², ³column², ³bbb², 12345
>  ³table², ³family², ³column², ³aaa², 12345
> I¹m getting three different values for identical
> table/family/qualifier/timestamp tuples.  Does this seem right?  There also
> doesn¹t seem to be a defined sort order, probably because the timestamps are
> identical.
> Also, if instead of using list(), I use getMap(), then I always only get a
> single result.  The single result is always the last item in the lists above
> (i.e., ³bbb² then ³bbb² then ³aaa²).  I get identical results from using
> getNoVersionMap().
> I suspect that this same behavior could occur when HBase decides to flush on
> its own, but I could be wrong.  As you can imagine, this can cause problems
> because clients can¹t know from the results of calling list() which value is
> ³right² or ³newest².  They also can¹t rely on getMap() or getNoVersionMap()
> because the single result that gets returned is not necessarily ³right² or
> ³newest².
> I¹ve reproduced everything above in a stand-alone installation and also with
> a 7 regionserver cluster with the final 0.20.3.  I started down this
> debugging path originally because I ran into this problem on the 7
> regionserver cluster with one table of 100+ regions.  I was flushing
> programmatically at the end of some large imports because I'm doing
> setWriteToWAL(false) for load performance.
> Am I doing something wrong?  Did I miss an HBase assumption about flushing
> and/or identical timestamps?
> Any help would be much appreciated.
> Thanks,
> Rod
> --
> Rod Cope
> CTO & Founder
> OpenLogic, Inc.

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