2010-06-23 22:42 keltezéssel, Bruce Momjian írta:
Boszormenyi Zoltan wrote:

we improved ECPG quite a lot in 9.0 because we worked and
still working with an Informix to PostgreSQL migration project.

We came across a pretty big performance problem that can be seen in
every "naive" application that uses only FETCH 1, FETCH RELATIVE
or FETCH ABSOLUTE. These are almost the only FETCH variations
usable in Informix, i.e. it doesn't have the grammar for fetching N rows
at once. Instead, the Client SDK libraries do caching themselves
behind the scenes to reduce network turnaround time.
I assume our ecpg version supports>1 fetch values, even in Informix
mode.  Does it make sense to add lots of code to our ecpg then?

I think, yes, it does make sense. Because we are talking
about porting a whole lot of COBOL applications.
The ESQL/C or ECPG connector was already written
the Informix quirks in mind, so it fetches only one record
at a time passing it to the application. And similar performance
is expected from ECPG - which excpectation is not fulfilled
currently because libecpg doesn't do the same caching as
ESQL/C does.

And FYI, I haven't added a whole lot of code, most of the
code changes in the patch is execute.c refactoring.
ECPGdo() was split into several functions, the new parts
are still doing the same things.

I can make the test case much smaller, I only needed
to test crossing the readahead window boundary.
This would also make the patch much smaller.

And this readahead is not on by default, it's only activated
by "ecpg -r fetch_readahead".

Best regards,
Zoltán Böszörményi

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