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A major transaction-processing feature, known as Transaction Dependent Creates/Deletes, supports the creation and deletion of Extended files under transaction control. For Standard files, the physical creation and deletion of files from disk is handled outside the scope of transaction control. In other words, Standard files do not support such operations as “aborting a create” or “rolling back a delete.”
If you are using ISAM to create the files with transaction control, Transaction Dependent Creates/Deletes are a best practice. (If you are using SQL to create the files with transaction control, this mode is automatically used.) The main benefit of this mode is helping automatic recovery to know which files should exist. When files are created without this mode, you may need to use SKIP_MISSING_FILES YES during recovery, which is discouraged except when specific error messages indicate it is necessary.
File creates and deletes may be part of a transaction and are subject to being undone in case of crashes, savepoint restores, and aborts. This is accomplished with the extended file mode ctTRANDEP. An Extended file with ctTRANDEP in its extended file mode is assumed to utilize transaction-dependent creates and deletes and must be created within a transaction. There is no special function call for transaction dependent creates or deletes.
If a different client attempts to open or create a file pending delete, DPND_ERR (643) is returned to signify that opens/creates must await the commit or abort of the delete.
To utilize a transaction-dependent delete with a file not created with ctTRANDEP, it will be necessary to update the file header to include the ctTRANDEP bit in the x8mode member of the extended header.
To support the rollback of a transaction-dependent file delete, which requires FairCom DB to maintain a copy of the old file after the delete is committed, use the ctRSTRDEL extended file mode. ctRSTRDEL automatically implies ctTRANDEP, but the reverse is not true. When only ctTRANDEP is used, the overhead of storing copies of an old file after its delete is committed is avoided.
A transaction-dependent create is only supported by the Xtd8 create routines, and requires an extended file mode with ctTRANDEP and/or ctRSTRDEL included. To perform a transaction-dependent create of a Standard FairCom DB file, call one of the create routines with ctNO_XHDRS and either ctTRANDEP or ctRSTRDEL included in the extended file mode. Including ctNO_XHDRS in the extended file mode causes the create routines to create a Standard file. If ctNO_XHDRS conflicts with other extended file mode bits, then the create will fail with XCRE_ERR (669).
To convert an existing Standard file to support transaction-dependent deletes, use calls of the form:
UpdateHeader(filno,ctTRANDEP,ctXFL_ONhdr);
or
UpdateHeader(filno,ctRSTRDEL,ctXFL_ONhdr);
However, these UpdateHeader() calls cannot convert a Standard file to an Extended file.
