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From Pan W <pwc...@gmail.com>
Subject Confusing the retrieve result with a given timestamp
Date Fri, 19 Nov 2010 05:17:20 GMT
Hi,

I am using hbase shell to verify some konwleges that I have read from
the post of "Understanding HBase and BigTable"

That post says:  "If an application asks for a given row at a given timestamp, 
HBase will return cell data where the timestamp is less than or equal to
the one provided."                                                      
After some experiments, I feel confused about  the concept of "less than" .

Describe details in the following :
1) create table:  
    create 'table', {NAME=>'cf1', VERSIONS=>3}

2) put some data in one cell with multi-version:
    put 'table', 'row1', 'cf1:c1' , 'aaaa',  16
    put 'table', 'row1', 'cf1:c1' , 'bbbb', 25
    put 'table', 'row1', 'cf1:c1' , 'dddd', 32

3) get data:
    get 'table', 'row1', {COLUMN=>'cf1:c1', TIMESTAMP=>19}

The result is NULL. 
As the post says,  The 'bbbb' with timestamp 16 that "less than" 19 should be returned, 
Why get nothing?
(p.s I write some java code to verify the "less than" concept  using
method setTimestamp(19) of class Get,  and get same result .  )


In addition, one more questions:
When I create table with parameter "VERSIONS=>3",  means in one cell
only has not more than three version datas, is right?
If right, when I put more data into same cell, such as:
     put 'table', 'row1', 'cf1:c1' ,'ffff', 42
Have four versions or three versions in this cell now?
why I can still retireve the oldest version data with timestamp 16?
    hbase(main):022:0>  get 'table', 'row1', {COLUMN=>'cf1:c1', TIMESTAMP=>16}  
   
    COLUMN                       CELL                                               
    cf1:c1                      timestamp=16, value=aaaa               


Sorry about the long mail,  any help will be appreciated.
-- 
Pan W <pwcrab@gmail.com>


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