Re: %lookup vs. chain

Mike Haston ** Data wrote:

I'm just noticing that as I spin through some large files that I'm chaining
out a million times (actually more) to a control file to check a flag.  In
the initial subroutine I'm setting up an array that I could easily store
this flag in.  I'm wondering what the opinion is as far as performance-wise
which is more efficient, doing the %lookup() on the array or chain to the
file?

Personally, I wouldn't worry about it unless you know for sure that
this is a particularly bad performance bottleneck in your
application. If performance improvement is a goal, test first to see
where the bottlenecks are, and concentrate on those areas.

If you do decide that this a bottleneck that needs addressing, be
sure to test any change you make. Sometimes, changing something with
the expectation that performance should improve may yield the
opposite effect. Performance tuning is sometimes tricky, and changes
may well have counter-intuitive results. (I know that well from my
own experience!)

The key aspects of performance tuning are test, test, test, and then
test some more.

(In general though, %LOOKUP on an ordered array should be faster
than a CHAIN. But be sure to put things into perspective. If only 5%
of the time is spent on that CHAIN, improving performance of that
step by, say, 60% will only yield a 3% improvement overall.)

Cheers!  Hans