Dbdelete

Utility: dbdelete.ec

Synopsis: This utility, was written to delete large numbers of rows while 
          using very few locks and avoiding long transaction problems.  The 
          performance of version 3 is on par with a dbaccess executed DELETE 
          statement while eliminating the problems with locks and transaction
          duration.  Versions 1&2 were too slow to be practical and version 1's
          source was overly complex, thus was born dbdelete.ec version 3.  Note 
          that in testing no throughput was gained from executing multiple
          copies of dbdelete with different WHERE clauses (unlike its
          progenitors ul.ec and dbcopy.ec).
        
Author(s): Art S. Kagel

Revision: 1.22

Features Version: 3.2

Version(s) supported: 7.xx, 8.xx, 9.xx

File(s): dbdelete.ec

Comments: Requires compilation by ESQL/C 7.xx or later.
 
Release Notes:
	Version 1.22 adds a new option, -q, which permits the user to specify a
	full SELECT statement to return ROWIDs or keys to select for deletion.
	If keys are returned then the -u option is required for -q to work
	properly (unexpected results may pursue you if you don't).

	Version 1.20 fixes a bug affecting 64bit compiles.  Thanks to Raja
	Nizad Ks for the feedback that led to this fix and for testing the
	patch.  Version 1.21 is cosmetic.

	Version 1.17 adds the -b CommitSize option and support for FET_BUF_SIZE
	environment variable to control transaction size.  Version 1.18
	increases the Features Versions to 3.2.  Version 1.19 fixes a typo.

	Version 1.16 removed some dead code and fixed the return type of
	usage(). 

	Version 1.14 makes the code safe to use with IDS 9.xx long object
	names.  Version 1.15 just updates the copyright statement.

	Version 1.13 adds a copyright message to the -V printout.  Not to
	worry, this is just a formality.  Use of this utility is still free.

	Version 1.12 fixed a missing break statement.

	OK, I give up.  Version 1.11 replaces itoa() for all systems with 
	sprintf().  The user support was no longer sensible for the few 
	cycles I gained on a handful of systems.

	Version 1.9 add #if defined()'s to better support compilation on AIX
	without GCC.  Version 1.10 uses the predefined _AIX rather than the
	standard __AIX__.
 
	Version 1.7 extends support for engines that do not support array
	fetch code.  Now builds the large IN clause anyway.  Version 1.8 is
	cosmetic only.

	Version 1.6 just improves portability.  The code uses itoa() to convert
	from integer to string, a function which is not universally available.
	There is now a #if near the top which uses numtos() on Sun systems 
	instead and if neither is available defines an inline function using 
	sprintf which you can enable by defining '-Dnoitoa' at compile time.

Notes:
        Delete by ROWID works by fetching a large number of matching rowids 
        (8191) and using them to build large delete statements with a WHERE
        rowid IN (...) clause.  The size of each of these delete statements 
        is controlled and limited by the -B option.  If the statement is too 
        large the time spent by the engine parsing and optimizing the large 
        statement reduces throughput.  On my testbed 2K was the best performer 
        overall and that is the default, YMMV so this is configurable!