At 11:07 AM 10/6/1999 -0700, Stan Sieler wrote:
>Jerry writes:
>
>> The other suggestion I would like to offer is it is actually better to
>> load the file at the same time it is initially created, vs creating/saving
>> the file and then loading it.
>
>Absolutely, if not quite for the reason Jerry mentions:
>
>> If it is built/loaded during the same
>> open, NMKSAM will leave some ventilation space within its structures at
>> certain iterations.
>
>I'm not sure that it leaves ventilation holes.  The real reason it's
>faster is that the initial creation is done before the file is
>attached to the transaction manager (XM).  This means the XM overhead
>is bypassed.  If you create the file and then fill it later, the
>updates go through XM.

Yep, I'd forgotten about this attribute of the initial loading of KSAM/iX.
However, the ventilation that is also done is important to NMKSAM files
which will have a lot of new data added to them.  This ventilation feature
applies only to NMKSAM files where the ;REUSE option is specified during the
file's initial loading at creation.  It was done to aid in the search for
open entries when adding entries to the file. This is because with the
;REUSE option, KSAM begins its search for an opening at the beginning of
the data area.  While this is assisted by checking a counter at each data
block, the process still serially searches for an opening. This is why the
performance NMKSAM and even IMAGE w/b-trees will be impacted after a lot of
new data has been added, and one of the reasons why performance will many
times improve after the NMKSAM/b-tree indexes have been re-built, providing
the replacement KSAM file is loaded as the same time it is built (which is
how DBUTIL approaches the adding/re-building of indexes).

So there you have it....2 excellent reasons to load data into a NMKsam file
at the same time its created vs. building an empty file and then re-opening
it to add data.


/jf
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