* implement materialized view
* modify code according to jihoonson's comments
* modify code according to jihoonson's comments - 2
* add documentation about materialized view
* use new HadoopTuningConfig in pr 5583
* add minDataLag and fix optimizer bug
* correct value of DEFAULT_MIN_DATA_LAG_MS
* modify code according to jihoonson's comments - 3
* use the boolean expression instead of if-else