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The FairCom transaction processing logic offers three modes of operation:
Transaction processing is covered in detail in Data Integrity.
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No transaction control
With no transaction control defined for a data file, the read/write access to the file will be very quick. However, no guarantee for data integrity will be available through atomicity or automatic recovery.
ctPREIMG
If just the ctPREIMG file mode is used, the database access will still be fast, and some data integrity will be provided through atomicity. With atomicity only, changes can be made on an all-or-nothing basis, but no automatic recovery is provided.
ctTRNLOG
If your application files have been setup with the ctTRNLOG file mode, all benefits of transaction processing are available to you, including atomicity and automatic recovery. Automatic recovery is only available with ctTRNLOG, because ctTRNLOG is the only mode where all changes to the database are written immediately to transaction logs. The presence of this transaction log, (history of changes to the files), allows the Server to guarantee the integrity of these files in case of a catastrophic event, such as a power failure. Recovering files without a ctTRNLOG file mode from a catastrophic event entails rebuilding the files.
Note: File rebuilding cannot recover data that was not flushed to disk prior to the catastrophic event.
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SUPPRESS_LOG_FLUSH
Full transaction processing offers the best possible data integrity, but at the expense of performance. Using SUPPRESS_LOG_FLUSH reduces overhead with transaction processing log flushes, at the expense of the automatic recovery. This keyword would only be used with the PREIMAGE_DUMP keyword described below.
PREIMAGE_DUMP
Although automatic recovery is not available to ctPREIMG files, it is possible to perform periodic dynamic backups. By using PREIMAGE_DUMP, it is possible to promote ctPREIMG files to full ctTRNLOG files during the dynamic dump process. The promotion to a ctTRNLOG file means that a full transaction log is maintained during the dump process. This process guarantees that any changes made to the files during the backup are saved in these specially maintained transaction logs. The ability to dynamically backup user data files minimizes the loss of the automatic recovery feature with this mode.
