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From "David S. Wang (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-5489) Add HTable accessor to get regions for a key range
Date Wed, 29 Feb 2012 05:46:02 GMT
Add HTable accessor to get regions for a key range

                 Key: HBASE-5489
                 URL: https://issues.apache.org/jira/browse/HBASE-5489
             Project: HBase
          Issue Type: Improvement
          Components: client
            Reporter: David S. Wang
            Assignee: David S. Wang
            Priority: Minor

It would be nice to have an accessor to find all regions that overlap with a particular range
of keys. Right now, the only way to accomplish that is to call HTable.getStartEndKeys(), then
follow that with calls to getRegionLocation() for the range of keys you are interested in.
 This algorithm has 2 drawbacks:

* It returns more keys than is necessary most of the time.  This is especially evident if
there are a lot of regions comprising the table and the range of keys is small.
* It always does a scan of .META. via MetaScannerVisitor for at least HTable.getStartEndKeys(),
and perhaps for HRegionLocations that are not already cached by the client.

An accessor that limited its scans to a specified range could avoid scanning .META. at all
if the HRegionLocations being fetched were already cached by the client, thereby potentially
making this operation faster in common cases.

Here's a proposal for the accessor:

   * Get the corresponding regions for an arbitrary range of keys.
   * <p>
   * @param startRow Starting row in range, inclusive
   * @param endRow Ending row in range, inclusive
   * @return A list of HRegionLocations corresponding to the regions that
   * contain the specified range
   * @throws IOException if a remote or network exception occurs
  public List<HRegionLocation> getRegionsInRange(final byte [] startKey,
    final byte [] endKey) throws IOException

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