question: protected void restoreBlobIntoMemory ( ) throws CacheException { String cacheFilePathAndName = getCacheFilePathAndName ( ) ; long begin = LOG . isTraceEnabled ( ) ? System . currentTimeMillis ( ) : 0 ; if ( LOG . isTraceEnabled ( ) ) LOG . trace ( "CACHE: Restoring matrix...  " + getVarName ( ) + "  HDFS path: " + ( _hdfsFileName == null ? "null" : _hdfsFileName ) + ", Restore from path: " + cacheFilePathAndName ) ; if ( _data != null ) throw new CacheException ( cacheFilePathAndName + " : Cannot restore on top of existing in-memory data." ) ; try { _data = readBlobFromCache ( cacheFilePathAndName ) ; } catch ( IOException e ) { throw new CacheException ( cacheFilePathAndName + " : Restore failed." , e ) ; } if ( _data == null ) throw new CacheException ( cacheFilePathAndName + " : Restore failed." ) ; if ( LOG . isTraceEnabled ( ) ) LOG . trace ( "Restoring matrix - COMPLETED ... " + ( System . currentTimeMillis ( ) - begin ) + " msec." ) ; }
target:  Low-level cache I/O method that physically restores the data blob to main memory. Must be defined by a subclass, never called by users.