package com.netflix.astyanax; import com.netflix.astyanax.connectionpool.exceptions.WalException; /** * Base interface for a write ahead log. The purpose of the WAL is to provide * atomicity and durability when writing to Cassandra. Before writing to * cassandra a record is written to the WAL which is assumed to stable storage * able to survive from a crash or hardware failure. After a crash the system * will inspect the WAL for records and replay them. If a record is successfully * written to cassandra it will be removed from the WAL. * * @author elandau * */ public interface WriteAheadLog { /** * Add an entry to WAL before it is sent to Cassandra. * * @param batch * @return */ WriteAheadEntry createEntry() throws WalException; /** * Remove an entry from the WAL after it was successfully written to * cassandra * * @param entry */ void removeEntry(WriteAheadEntry entry); /** * Read the next entry to retry from the wall. Call remove if successful or * retryEntry if unable to write to cassandra. * * @return */ WriteAheadEntry readNextEntry(); /** * Retry an entry retrieved by calling getNextEntry(); * * @param entry */ void retryEntry(WriteAheadEntry entry); }