Re: how to sort a file in place?

On 23 Jan 2013 10:42, Dan Kimmel wrote:

What does RGZPFM actually accomplish. We know only two things.

1) it eliminates deleted records

2) it changes the RRN to match the order of the index given in
KEYFILE.

We don't know that it actually arranges the records of the table
in anything resembling sequential order, though it does give that
appearance when using DSPPFM.

While I normally would agree and argue similarly, that the
implementation may not match the effect, in this case the actual
implementation is unlikely to change. And being a LIC implementation
rather than an OS implementation detail, that is at least somewhat
irrelevant because user code both remains blissfully unaware and can not
incorrectly code dependency upon an implementation detail that might change.

I know that the physical order of data is arranged sequentially
within the data segments of the dataspace, and the segments of the
dataspaces are logically ordered sequentially regardless that they are
physically scattered on DASD.

I know that DSPPFM obtains the data using the arrival access path. I
for some time had /owned/ the code QNFBROWS that implements the feature.

We assume that it reorganizes data into some efficient structure.
We know this only because some sequential accesses have improved
performance. How that is actually accomplished probably has no
relationship to any kind of sequential organization of the physical
records.

I actually know rather than merely assume how the database always had
organized the data; I am lucky that way :-) but anyone with STRSST D/A/D
capability can dump a dataspace to see the effects. And just as the
RGZPFM help text suggests, the reorganization of the data [if requested,
beyond just compressing out deleted records] is accomplished by
physically sequencing\collating the rows to match the Access Path from
the KEYFILE specification. The LIC-implemented [i.e using the
ALWCANCEL(*NO) of RGZPFM] reorganize feature effectively copies all of
the data and creates new segments filled with the ordered data, and if
the request is not canceled then the existing dataspace is assigned that
new ordered collection of segments, and the LIC frees the storage by
destroying the old data segments.

I know that for sequential access method the database will generally
not fault database pages because retrieval via the arrival access path
knows the next segment in [logical] sequence to be paged without
faulting. So, the reorganized data enables better performance for
sequential access specifically because the data is actually arranged in
its physical ordering within and across logically ordered segments that
match the arrival sequence access path.

CRPence on Wednesday, January 23, 2013 12:30 PM wrote:

On 23 Jan 2013 07:23, Stone, Joel wrote:

I would like to sort WORKFILE1 in place, preferably using SQL.

Something to consider is "What is the reason for wanting to do
so?"; and having shared that, contributors might offer
alternatives.

Is this possible?

In effect, yes, but not with SQL. The RGZPFM CL command provides a
means to reorganize the physical data in a database physical file
member.

Physical order of data is inconsequential to the relational model;
i.e. where data is unordered sets. And so for SQL as a language to
provide data access for the RDBMS, there is effectively nothing
that the SQL provides to physically order the data within a TABLE.
Collation is an attribute of the request to extract data [the
run-time SELECT], rather than an attribute of the physical data.
That is because there can be many different possible collations for
the same set of data; most notably, DESCending vs ASCending, but
also according to data encoding and language\locale preferences,
and across any variety of expressions\columns.

Or must I create another table with SQL CREATE and then CPYF it
back to the original file.

That is one of a number of ways to effect a desired physical
order. But the value from doing so is limited, except for a static
TABLE and for the arrival sequence access method.

The above should say "sequential access method"... which is using the
"arrival sequence access path".

My preference is to use the RGZPFM with the KEYFILE parameter
naming an access path that defines my desired collation.