Re: %lookup on a Data Structure Array

Hi, Kurt:

Loading the entire file into one or more arrays will incur the overhead
of loading the entire file for each job that needs to search the array,
and this increases the virtual storage used by each and every job that
needs to access this file.

So, before you decide to load all records of this file into an array and
search using a binary search, consider the following alternatives:

#1. issue SETOBJACC to load the entire *FILE into a dedicated memory
pool; sized based on the size of the file; this will speed up access for
all jobs using this file, without any coding changes to the programs
using the *FILE.

#2. create a "server" job that loads the array, and communicates with
requester jobs via data queues. Instead of loading every record into
the array, start out with an empty array, or load just one record. When
a client program sends a message to the request data queue, requesting a
"look-up", the server job first looks in the local "cache" (the array),
and if not found, it then chains out to the file, and adds that record
to the "cache" array, so any subsequent look-ups for that record will be
faster, before returning the results via a results data queue (one per
client). Typically each client sends the name of its results data queue
as part of the request message. The server job will need to maintain a
counter of how many records are in the array, for use on the %lookup BIF.

#3. create a user index, and load the data into the user index, and use
the MI builtin function _FNDINXEN to do the look-up. This should be
faster than database I/O, but you will have to incur the overhead to
initially load the user index. Note that you can do this just once, and
use an insert, update and delete trigger attached to the file to
maintain the *USRIDX whenever the corresponding file is changed. All
users or jobs can then share this one *USRIDX object.

_Performance trade-offs_
On average, how many records or rows of this *FILE would be accessed by
any given job or interactive user session, in a given day? What
percentage of the total file?

Hope that helps,

Mark S. Waterbury