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From Ric Wang <wqt.w...@gmail.com>
Subject Re: for one specific row: are the values of all columns of one family stored in one physical/grid node?
Date Wed, 10 Jun 2009 16:07:59 GMT

By saying "columns for key1 will not be on all the nodes but just one node
in the cluster", you really mean "columns of the SAME family for key1...",

Please correct me if I am wrong, but I think for the row key "key1", the
data value of "familyA:lableX" and that of "familyB:labelY" can still be
stored on two different nodes because they are in two different families. Is
that correct?

Thanks in advance for your clarification.

On Tue, Jun 9, 2009 at 8:35 PM, Billy Pearson <sales@pearsonwholesale.com>wrote:

> You should read over the
> http://wiki.apache.org/hadoop/Hbase/HbaseArchitecture
> The data is sorted by row key, then column:label, timestamp
> In that order so if you have row key1 all the labels for columnval1 will be
> stored together in the same file
> We do flush more the one file to disk as data is added so the values are
> not always stored together until after a major compaction/merge all store
> files together
> But what we mean by stored together is all column1 will be stored in one
> file and column2 would be stored in a separate set of files so if you only
> one data from column1 then you only need to read the data from one set of
> files not all the columns for that row key.
> also columns for key1 will not be on all the nodes but just one node in the
> cluster. The table is split by the key values so keys1-100 would be one
> region keys101-200 would be another region all in the same table
> We split when the size get to large they split and become two regions and
> so on.
> So we look up a key we only have to look at one server
> Billy
> "Ric Wang" <wqt.work@gmail.com> wrote in message
> news:21224f560906091155i6bb9b6e1xc59095a01bbc2d50@mail.gmail.com...
>  Hi,
>> Very new to Hadoop and HBase. And sorry about the rudimentary question:
>> I store my artifacts as rows in an HBase table, and the attributes of each
>> artifact as labels within one single column family (ex. myFamily). I may
>> have tens of thousands of labels, and millions and millions of rows. Now
>> as
>> the data size grows, some document says that, the values of one family
>> will
>> be "stored together". I wonder what that really means.
>> For example, for a given row key (my.key.123), will HBase guarantee that
>> ALL
>> its attributes (ie. the values of ALL the labels in "myFamily") of that
>> row
>> key be stored on one physical/grid node? In other words, if I want to find
>> out ONE contain matching row key "my.key.123" based on its attributes
>> (column values), at the implementation level, will HBase be
>> 1. traversing all the distributed nodes and interrogating the column
>> values;
>> aggregating the results coming from all the nodes; and finally finding out
>> the matching row key
>> or
>> 2. doing atomic operations in parallel on each node locally; and finally,
>> only one node will return the matching row key (if there is a match).
>> My guess is the that the answer depends on if all attributes (in myFamily)
>> of a given row are stored on one and only one node.
>> Hope I didn't make my question very confusing. Very new to column based
>> database; please help and bare with me.
>> Thanks!
>> Ric

Ric Wang

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