My recent project had some issues with hashing some 10 million numbers. To analyze the matter I wrote a small test program, see numberhash.c.
I wanted to know which influence the following factors play:
- hashing just numbers (no alphabetic characters)
- ASCII vs. EBCIDC
- choice of hash function
- load factor
- distribution of collisions
Recently I learned the hard way that IBM Enterprise COBOL compiler cannot generate 8-byte long POINTER variables, but only 4-byte pointers, meaning, that you cannot use more than 2GB in COBOL on a mainframe. I.e., you cannot make use of AMODE=64 with COBOL on the mainframe. You can run in AMODE=64, but you cannot exploit it. BTW, we have the year 2013. So, no big-data on mainframe with COBOL.
IBM Assembler and C/C++ can fully exploit AMODE=64, i.e., can use 8-byte long pointers.
Mainframe rehosting is about replacing the whole mainframe with one or multiple Linux boxes, or at times, move portions of the application landscape from the mainframe to Linux. Thereby you basically keep many of the hitherto used development- and runtime-environment, like COBOL, DB2, IMS, CICS, etc. The goal in mainframe rehosting is to dramatically reduce costs. If you are dauntless you can also move to Windows.
The point is that you do not rewrite your applications but rather just move your applications, i.e., you recompile your applications on new hardware. So all accumulated experiences with the software is fully preserved.
In 2008 I started writing a paper on mainframe rehosting, see Mainframe Rehosting.
During 2008-2011 the paper has been revised somewhat. The paper is in German.