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From Jim Kellerman <...@powerset.com>
Subject RE: Does HBase have a index?
Date Thu, 06 Mar 2008 16:33:38 GMT
Each cell in HBase has a key which is a tuple consisting of
row-key column-family:column-member and timestamp

Large tables are broken into row ranges called regions.

All the members of a single column family are stored together
in a file.

Thus the row key is used to find the region and the column family
is used to find the the file.

Each file has a sparse index composed of the row/column/timestamp
keys, so finding a particular cell involves binary searching the
index (which is kept in memory).

---
Jim Kellerman, Senior Engineer; Powerset


> -----Original Message-----
> From: Bin YANG [mailto:yangbinisme82@gmail.com]
> Sent: Thursday, March 06, 2008 12:40 AM
> To: hadoop-user@lucene.apache.org
> Subject: Does HBase have a index?
>
> Dear colleagues,
>
> I have a questions on HBase's index implementation.
>
> How does the HBase find the data according to a row key? Use
> a index like database, or use a hash function?
> I suppose that a hash function which hash row key to physical
> address is more efficient.
>
> As we know, a big table in HBase is stored as several Small
> tables, each table stores attributes in a column family.
> So that, each row may be stored in several small tables.
> Does a hash function hash row key to many physical address?
> Each physical address correspond to a small table which
> contains the row key?
>
> Does anybody have idea on how to create a index on other attribute?
>
> Best,
> Bin YANG
> --
> Bin YANG
> Department of Computer Science and Engineering Fudan
> University Shanghai, P. R. China
> EMail: yangbinisme82@gmail.com
>
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> Date: 3/5/2008 9:50 AM
>
>

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