org.apache.lucene.index

## Interface TwoPhaseCommit

All Known Implementing Classes:
  IndexWriter

    public interface TwoPhaseCommit

An interface for implementations that support 2-phase commit. You can use `TwoPhaseCommitTool` to execute a 2-phase commit algorithm over several `TwoPhaseCommit`s.

WARNING: This API is experimental and might change in incompatible ways in the next release.

### Method Summary

All Methods Instance Methods Abstract Methods
`long` `commit()` The second phase of a 2-phase commit.
`long` `prepareCommit()` The first stage of a 2-phase commit.
`void` `rollback()` Discards any changes that have occurred since the last commit.

### Method Detail

#### prepareCommit

    long prepareCommit()
                throws IOException

The first stage of a 2-phase commit. Implementations should do as much work as possible in this method, but avoid actual committing changes. If the 2-phase commit fails, `rollback()` is called to discard all changes since last successful commit.

Throws:
  `IOException`

#### commit

    long commit()
         throws IOException

The second phase of a 2-phase commit. Implementations should ideally do very little work in this method (following `prepareCommit()`, and after it returns, the caller can assume that the changes were successfully committed to the underlying storage.

Throws:
  `IOException`

#### rollback

    void rollback()
           throws IOException

Discards any changes that have occurred since the last commit. In a 2-phase commit algorithm, where one of the objects failed to `commit()` or `prepareCommit()`, this method is used to roll all other objects back to their previous state.

Throws:
  `IOException`