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From Rod Cope <rod.c...@openlogic.com>
Subject Re: Problem with flushing and identical timestamps
Date Wed, 27 Jan 2010 02:00:43 GMT
Thanks for the extra details, St.Ack.

I mean quit my client.  Let me know if any additional testing would help
narrow it down.


On 1/26/10 Tuesday, January 26, 20105:48 PM, "Stack" <stack@duboce.net>

> Here's a bit more on the below:
> https://issues.apache.org/jira/browse/HBASE-1485.
> 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
> detail.
> St.Ack
> 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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