• Durability - Once a transaction has been committed, the resultant changes are not lost regardless of the circumstances, such as system failure.
ALTIBASE HDB guarantees reliable transactional processing by implementing a database server that satisfies all ACID requirements.
Durability means that after a transaction has been committed, the committed transaction must be guaranteed, even if a database failure occurs before the changed data are physically written to a disk.
ALTIBASE HDB provides durability with a combination of checkpointing and transaction logging.
ALTIBASE HDB adheres to WAL (write-ahead logging) protocol. Based on WAL protocol, before overwriting an object with "uncommitted" updates, ALTIBASE HDB writes the log records related to such updates to disk storage for UNDO operations. And similarly, before committing an update to a database object, it writes the log records related to such an update to the log on disk storage for REDO operations.
Durability & Performance
In ALTIBASE HDB transaction durability has a significant influence on the processing performance. Especially on the memory-based side of the database which can potentially exhibit performance up to 20 times faster than the disk-based side of the database, guaranteeing transaction durability has a much bigger impact on performance. This is due the fact that based on the WAL protocol, in order for a ALTIBASE HDB to provide complete transaction durability, it has to write logs for all database updates to a log file on disk therefore introducing additional disk I/O activity which can degrade the performance.
Relaxed Durability (Level 2)
When using ALTIBASE HDB Relaxed durability setting, on a system or a database crash, recovery point is the last checkpoint. This level is suitable for use in business environments in which database durability is not critical, but fast processing of transactions is required. Businesses that can tolerate a certain level of data loss may want to take advantage of this level for high performance transactions.
Enhanced Durability (Level 3)
When using ALTIBASE HDB Enhanced durability setting, on database crash there is no data loss, and the recovery point is the last point where OS syncs kernel buffer to disk. In other words, even if the database crashes, durability is still ensured by the OS. This level is suitable for environments characterized by low rates of failures such as OS crashes, hardware faults and power outages. Businesses that can tolerate a certain level of data loss may want to take advantage of this level. This is the default setting for ALTIBASE HDB.
Strict Durability (Level 5)
When using ALTIBASE HDB Strict durability setting, since each transaction committed only when written to disk, there will be no data loss with either system or database crash, This level is suitable for use in business environments in which data durability is more important than faster performance. Businesses that cannot tolerate any kinds of data loss should use this level.