[HADOOP-2555] Refactor the HTable#get and HTable#getRow methods to avoid repetition of retry-on-failure logic

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 0.17.0
• Assignee: Bryan Duxbury
• Reporter: Peter Dolan
• Created: 08/Jan/08 23:18
• Updated: 21/May/08 20:05
• Resolved: 01/Feb/08 01:18

Description

The following code is repeated in every one of HTable#get and HTable#getRow methods:

HTable.java

    MapWritable value = null;
    for (int tries = 0; tries < numRetries; tries++) {
      HRegionLocation r = getRegionLocation(row);
      HRegionInterface server =
        connection.getHRegionConnection(r.getServerAddress());
      
      try {
        value = server.getRow(r.getRegionInfo().getRegionName(), row, ts);  // This is the only line of code that changes significantly between methods
        break;
        
      } catch (IOException e) {
        if (e instanceof RemoteException) {
          e = RemoteExceptionHandler.decodeRemoteException((RemoteException) e);
        }
        if (tries == numRetries - 1) {
          // No more tries
          throw e;
        }
        if (LOG.isDebugEnabled()) {
          LOG.debug("reloading table servers because: " + e.getMessage());
        }
        tableServers = connection.reloadTableServers(tableName);
      }
      try {
        Thread.sleep(this.pause);
        
      } catch (InterruptedException x) {
        // continue
      }
    }

This should be factored out into a protected method that handles retry-on-failure logic to facilitate more robust testing and the development of new API methods.

Proposed modification:

// Execute the provided Callable against the server
protected <T> callServerWithRetries(Callable<T> callable) throws RemoteException;

The above code could then be reduced to:

HTable.java

    MapWritable value = null;
    final connection;
    try {
      value = callServerWithRetries(new Callable<MapWritable>() {
            HRegionLocation r = getRegionLocation(row);
            HRegionInterface server =
                connection.getHRegionConnection(r.getServerAddress());
            server.getRow(r.getRegionInfo().getRegionName(), row, ts);
          });
    } catch (RemoteException e) {
      // handle unrecoverable remote exceptions
    }

This would greatly ease the development of new API methods by reducing the amount of code needed to implement a new method and reducing the amount of logic that needs to be tested per method.