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From Lars George <lars.geo...@gmail.com>
Subject Re: Confirming a Bug
Date Mon, 19 Mar 2012 09:58:26 GMT
Hi Peter,

Lars #1 here again :)

That is fine, the caching is done transparently for you. But what I also suggest is counting
the number of KeyValues you get back, just to confirm. In other words, iterate over the result
and check how many actual KVs you get back. The reason I am asking is that for example scanner
batching will change the behavior, you will get a Result instance per batch, not per row.

Thanks for digging in!

Lars

On Mar 19, 2012, at 12:40 AM, Peter Wolf wrote:

> Excellent!   Thank you very much (other) Lars.
> 
> I have only tested this one one dataset, and only on a few values of caching.  I certainly
get different results with 10,000 5,000 and 1,000 caching.  1,000 gives me the same results
as default.  I also get different results when I add families to the Scan.
> 
> I seem to be surpassing some maximum buffer size.  The number of results is always the
correct value - some multiple of the cache size.  For example, the correct value was 24,452,
but when caching was set to 10,000, I got 4,452 results.  When I then removed a family from
the scan, I got 14,452 results.
> 
> I'll try to write a standalone program to reproduce this.  I'll get back to you soon.
> 
> P
> 
> P.S.  I just want to check.  The following code counts the number of results.  I don't
need to do anything to "get the next cache" or something do I?
> 
>         Iterator<Result>   it = scanner.iterator();
>         while (it.hasNext()) {
>             Result result = it.next();
>             ...
>         }
> 
> 
> 
> 
> On 3/18/12 5:51 PM, lars hofhansl wrote:
>> Hi Peter,
>> 
>> (this is the other Lars)
>> 
>> 
>> Does this depend on your dataset at all? Does not it also happen for smaller value
of scanner caching?
>> 
>> 
>> Any chance that you can reproduce this in a unittest and file a jira?
>> If you do (specifically the test), I'll promise I'll look at it this week :)
>> 
>> 
>> -- Lars (H)
>> 
>> 
>> 
>> ________________________________
>>  From: Peter Wolf<opus111@gmail.com>
>> To: user@hbase.apache.org
>> Sent: Sunday, March 18, 2012 7:13 AM
>> Subject: Re: Confirming a Bug
>> 
>> Hi Lars,
>> 
>> I don't think so...  My behavior is definitely tied to the amount of
>> data in each Result.  There definitely seems to be some sort of
>> threshold.  Changing the caching amount produces a completely repeatable
>> behavior.  10,000, 5,000, and 1000 each produce different repeatable
>> results, and changing the families added as produces different reliable
>> results. There is no "sometimes" or "occasional", and if there was a
>> Major Compaction, it wouldn't happen that often.
>> 
>> https://issues.apache.org/jira/browse/HBASE-5121
>> https://issues.apache.org/jira/browse/HBASE-2856
>> 
>> Note that with all my families added each result is a few 1000 bytes
>> big.  Is that unusually large?
>> 
>> Thanks
>> P
>> 
>> 
>> 
>> On 3/18/12 5:28 AM, Lars George wrote:
>>> Hi Peter,
>>> 
>>> Could you be hitting HBASE-5121? Or even HBASE-2856?
>>> 
>>> Lars
>>> 
>>> On Mar 17, 2012, at 20:46, Peter Wolf<opus111@gmail.com>   wrote:
>>> 
>>>> Hello,
>>>> 
>>>> A couple of days ago, I asked about strange behavior in my "Scan.addFamiliy
reduces results" thread.
>>>> 
>>>> I want to confirm that I did find a bug, and if so, how to submit a bug report.
>>>> 
>>>> The basic strangeness is that changing the amount of caching, changes the
number of results.  In the original thread, this was confused by the fact that adding different
families also changed the number of results.  We thought it was a filtering problem.
>>>> 
>>>> However, changing nothing but the setCaching() value changes the number of
results.  Furthermore, the result difference is a multiple of the setCaching() value.
>>>> 
>>>> Here is the pseudo code:
>>>> 
>>>>          Scan scan = new Scan(...);
>>>>          scan.addFamily(...);
>>>>          Filter filter = ...
>>>>          scan.setFilter(filter);
>>>> 
>>>> -->       scan.setCaching(10000);<--
>>>> 
>>>>          scanner = hTable.getScanner(scan);
>>>>          Iterator<Result>   it = scanner.iterator();
>>>>          while (it.hasNext()) {
>>>>              Result result = it.next();
>>>>              ...
>>>>          }
>>>> 
>>>> 
>>>> Thank you
>>>> Peter
> 


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