Re: CHGPF

[CRPence <CRPbottle@xxxxxxxxx>]

James Lampert wrote:
> Hmm. I don't recall ever hearing of a CHGPF command before. Yet our
> V4R4 development box appears to have one.
>
> Does it really allow one to restructure a PF without having to go 
> through the old turkey-trot of renaming it, compiling the new
> version, and copying the records over? Are there any limitations,
> compared with doing it the old-fashioned way?
>
> And when did IBM slip it in without our noticing?

  CHGPF is what it was since S/38, plus some more; to change attributes 
of both the physical file itself [e.g. MAXMBRS()] and for the members 
that exist or are added, their attributes acquired from the file [e.g. 
SIZE()].

  It is the specific invocation CHGPF SRCFILE() which is /like/ an SQL 
ALTER.  The CHGPF SRCFILE() does the rename, create from source, data 
copy, owner change, grant with reference, journal to the new file, 
recreate logicals to refer to the new physical, LF owner change, LF 
grant with reference, journal new access path, and then delete the old 
files.  The copy process allows transfer of some existing access paths 
[index objects] from the old files to the new files versus rebuild which 
is typically one of the longest portions of the manual process, and when 
resource limitations require it, the copy is done in /chunks/ to remove 
the requirement to have two full copies of data on the system.

  The limitations are fewer than manual, but a review of the DSPDBR 
RCDFMT(*ALL) of the PF should be done to know what LF will change, and 
that the exception of that list from DSPDBR RCDFMT(*NONE) represents 
those LF that will not change; the manual method results, will depend on 
the DDS and/or methods used for creating the LF.

  Re reference to V4: I would recommend to avoid ALTER on any releases 
no longer supported, and especially to *never* alter to add a column to 
a file that was created on V5R# and saved back to V4R#.  Actually that 
may not be the VRM boundary of concern; it is whatever release boundary, 
for which database file record format conversions took place, since the 
ALTER capability was added.

Regards, Chuck