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From "Samuel Guo (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HAMA-88) DenseMatrix.close should not delete the table that are aliased in HamaAdmin.
Date Fri, 24 Oct 2008 02:59:44 GMT

    [ https://issues.apache.org/jira/browse/HAMA-88?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12642370#action_12642370

Samuel Guo commented on HAMA-88:

My proposal will be:

1. change Matrix.getName() to Matrix.getPath(). 
 As my first comment, a path means the path to store the matrix'data. In DenseMatrix, it means
a tablename in HBase.

2. change the HamaAdmin interface to make the logic clear.
HamaAdmin is a manager of the mapping a matrix aliase name to a matrix's path.

public interface HamaAdmin {

   * Saves matrix as name 'AliaseName'
   * @param matrix
   * @param aliaseName
   * @return true if it saved
  public boolean save(Matrix matrix, String aliaseName);

   * Get a matrix aliased as 'AliaseMatrixName'
   * @param aliaseName
   * @return Matrix, if there is a matrix aliased as "aliaseMatrixName", otherwise null.
  public Matrix load(String aliaseMatrixName);

   * @param AliaseMatrixName
   * @return true if matrix is exist
  public boolean matrixExists(String aliaseMatrixName);

   * remove the aliaseMatrixName.
   * if the matrix has other aliaseMatrixNames, this method will not delete matrix.
   * if the matrix has no any more aliaseMatrixName, this method finally delete the matrix.
   * @param matrixName
   * @throws IOException
  public void remove(String matrixName) throws IOException;

   * Deletes the matrix, and also remove all its aliaseMatrixNames store in HamaAdmin.
   * @param matrixName
   * @throws IOException
  public void delete(String matrixName) throws IOException;


3. add an attribute in DenseMatrix "attribute:aliases" to count the number of aliasename store
in HamaAdmin.
1) DenseMatrix.close() will see the "attribute:aliases" to see if any aliasename stored in
HamaAdmin aliase this matrix. if not, we delete the matrix while we closing it. if so, we
just disconnect the connnection to the matrix's table in HBase.
2) HamaAdmin.save() will increment the "attribute:aliases" of a matrix. HamaAdmin.decrement
it. "attribute:aliase" acts like a reference count in garbage collection. we will know when
we doesn't need the matrix'table.

4. move "public DenseMatrix(HamaConfiguration conf, String matrixName)" to "protected DenseMatrix(...)".
so we don't expose this constructor to the user. And this constructor is used in HamaAdmin
to load a matrix from an existed matrix's table.

Above are just my thoughts. Welcome for comments :-)

> DenseMatrix.close should not delete the table that are aliased in HamaAdmin.
> ----------------------------------------------------------------------------
>                 Key: HAMA-88
>                 URL: https://issues.apache.org/jira/browse/HAMA-88
>             Project: Hama
>          Issue Type: Bug
>    Affects Versions: 0.1.0
>            Reporter: Samuel Guo
>             Fix For: 0.1.0
> for example:
> "
> String matrixname = "MatrixA";
> Matrix a = DenseMatrix.random(conf, 10, 10);
> a.save(matrixname);
> a.close();
> Matrix b = new DenseMatrix(conf, matrixname);
> "
> If we close a matrix, we alse delete the table in hbase. so we can use its aliase name
keeped in HamaAdmin to reopen the matrix.
> so we need to identify if the matrix has been keeped in HamaAdmin. If the matrix has
been aliased in HamaAdmin, we should not delete the table in Hbase. 

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