===== 특징 =====
* java 만 지원.
* Two Phased Locking 지원
===== Two Phased Locking with Snapshot Isolation =====
* This model is referred to as MVLOCKS. It works the same way as normal 2PL as far as updates are concerned.
* SNAPSHOT ISOLATION is a multiversion concurrency strategy which uses the snapshot of the whole database at the time of the start of the transaction.
* In this model, readonly transactions use SNAPSHOT ISOLATION. While other sessions are busy changing the database, the readonly session sees a consistent view of the database and can access all the tables even when they are locked by other sessions during updates.
* There are many applications for this mode of operation. In heavily updated data sets, this mode allows uninterrupted read access to the data.
* 즉. select 하는 커넥션은, update하는 커넥션에 영향을 받지 않고, 스냅샷된 테이블을 쿼리한다.