Program: 5547
Project: 5547
Buggy source:
/** 
 * Deletes meta data until a given time, while keeping the latest meta data even if less than tillTime.
 * @param tillTime time till the meta data will be deleted.
 * @param callback callback called before deleting a meta data column.
 * @return total number of columns deleted.
 */
public int cleanMetaData(final long tillTime,final DeleteCallback callback) throws Exception {
  return execute(new TransactionExecutor.Function<Table,Integer>(){
    @Override public Integer apply(    Table table) throws Exception {
      int deletedColumns=0;
      try (Scanner scanner=table.scan(ROW_KEY_PREFIX,ROW_KEY_PREFIX_END)){
        Row row;
        while ((row=scanner.next()) != null) {
          byte[] rowKey=row.getRow();
          final NamespaceId namespaceId=getNamespaceId(rowKey);
          String namespacedLogDir=impersonator.doAs(namespaceId,new Callable<String>(){
            @Override public String call() throws Exception {
              return LoggingContextHelper.getNamespacedBaseDirLocation(namespacedLocationFactory,logBaseDir,namespaceId,impersonator).toString();
            }
          }
);
          for (          final Map.Entry<byte[],byte[]> entry : row.getColumns().entrySet()) {
            try {
              byte[] colName=entry.getKey();
              URI file=new URI(Bytes.toString(entry.getValue()));
              if (LOG.isDebugEnabled()) {
                LOG.debug("String_Node_Str",file,Bytes.toLong(colName));
              }
              Location fileLocation=impersonator.doAs(namespaceId,new Callable<Location>(){
                @Override public Location call() throws Exception {
                  return rootLocationFactory.create(new URI(Bytes.toString(entry.getValue())));
                }
              }
);
              if (!fileLocation.exists()) {
                LOG.warn("String_Node_Str",file);
                table.delete(rowKey,colName);
                deletedColumns++;
              }
 else               if (fileLocation.lastModified() < tillTime) {
                callback.handle(namespaceId,fileLocation,namespacedLogDir);
                table.delete(rowKey,colName);
                deletedColumns++;
              }
            }
 catch (            Exception e) {
              LOG.error("String_Node_Str",Bytes.toString(entry.getValue()),e);
            }
          }
        }
      }
       return deletedColumns;
    }
  }
);
}

Fixed version (ground truth):
/** 
 * Deletes meta data until a given time, while keeping the latest meta data even if less than tillTime.
 * @param tillTime time till the meta data will be deleted.
 * @param callback callback called before deleting a meta data column.
 * @return total number of columns deleted.
 */
public int cleanMetaData(final long tillTime,final DeleteCallback callback) throws Exception {
  return execute(new TransactionExecutor.Function<Table,Integer>(){
    @Override public Integer apply(    Table table) throws Exception {
      int deletedColumns=0;
      try (Scanner scanner=table.scan(ROW_KEY_PREFIX,ROW_KEY_PREFIX_END)){
        Row row;
        while ((row=scanner.next()) != null) {
          byte[] rowKey=row.getRow();
          final NamespaceId namespaceId=getNamespaceId(rowKey);
          String namespacedLogDir=null;
          try {
            namespacedLogDir=impersonator.doAs(namespaceId,new Callable<String>(){
              @Override public String call() throws Exception {
                return LoggingContextHelper.getNamespacedBaseDirLocation(namespacedLocationFactory,logBaseDir,namespaceId,impersonator).toString();
              }
            }
);
          }
 catch (          Exception e) {
            if (e instanceof NamespaceNotFoundException) {
              LOG.warn("String_Node_Str",namespaceId.getEntityName(),e);
            }
 else {
              LOG.warn("String_Node_Str",namespaceId.getEntityName(),e);
              continue;
            }
          }
          for (          final Map.Entry<byte[],byte[]> entry : row.getColumns().entrySet()) {
            try {
              byte[] colName=entry.getKey();
              URI file=new URI(Bytes.toString(entry.getValue()));
              if (LOG.isDebugEnabled()) {
                LOG.debug("String_Node_Str",file,Bytes.toLong(colName));
              }
              if (Strings.isNullOrEmpty(namespacedLogDir)) {
                LOG.warn("String_Node_Str" + "String_Node_Str",Bytes.toString(entry.getValue()),namespaceId.getEntityName());
                table.delete(rowKey,colName);
                deletedColumns++;
                continue;
              }
              Location fileLocation=impersonator.doAs(namespaceId,new Callable<Location>(){
                @Override public Location call() throws Exception {
                  return rootLocationFactory.create(new URI(Bytes.toString(entry.getValue())));
                }
              }
);
              if (!fileLocation.exists()) {
                LOG.warn("String_Node_Str",file);
                table.delete(rowKey,colName);
                deletedColumns++;
              }
 else               if (fileLocation.lastModified() < tillTime) {
                callback.handle(namespaceId,fileLocation,namespacedLogDir);
                table.delete(rowKey,colName);
                deletedColumns++;
              }
            }
 catch (            Exception e) {
              if (e instanceof NamespaceNotFoundException) {
                LOG.warn("String_Node_Str",Bytes.toString(entry.getValue()),namespaceId.getEntityName());
              }
 else {
                LOG.error("String_Node_Str",Bytes.toString(entry.getValue()),e);
              }
            }
          }
        }
      }
       return deletedColumns;
    }
  }
);
}