Thread: Re: how to speed up 002_pg_upgrade.pl and 025_stream_regress.pl under valgrind

Tomas Vondra <tomas@vondra.me> writes:
> [ 002_pg_upgrade and 027_stream_regress are slow ]

> I don't have a great idea how to speed up these tests, unfortunately.
> But one of the problems is that all the TAP tests run serially - one
> after each other. Could we instead run them in parallel? The tests setup
> their "private" clusters anyway, right?

But there's parallelism within those two tests already, or I would
hope so at least.  If you run them in parallel then you are probably
causing 40 backends instead of 20 to be running at once (plus 40
valgrind instances).  Maybe you have a machine beefy enough to make
that useful, but I don't.

Really the way to fix those two tests would be to rewrite them to not
depend on the core regression tests.  The core tests do a lot of work
that's not especially useful for the purposes of those tests, and it's
not even clear that they are exercising all that we'd like to have
exercised for those purposes.  In the case of 002_pg_upgrade, all
we really need to do is create objects that will stress all of
pg_dump.  It's a little harder to scope out what we want to test for
027_stream_regress, but it's still clear that the core tests do a lot
of work that's not helpful.

            regards, tom lane

On 9/15/24 20:31, Tom Lane wrote:
> Tomas Vondra <tomas@vondra.me> writes:
>> [ 002_pg_upgrade and 027_stream_regress are slow ]
> 
>> I don't have a great idea how to speed up these tests, unfortunately.
>> But one of the problems is that all the TAP tests run serially - one
>> after each other. Could we instead run them in parallel? The tests setup
>> their "private" clusters anyway, right?
> 
> But there's parallelism within those two tests already, or I would
> hope so at least.  If you run them in parallel then you are probably
> causing 40 backends instead of 20 to be running at once (plus 40
> valgrind instances).  Maybe you have a machine beefy enough to make
> that useful, but I don't.
> 

I did look into that for both tests, albeit not very thoroughly, and
most of the time there were only 1-2 valgrind processes using CPU. The
stream_regress seems more aggressive, but even for that the CPU spikes
are short, and the machine could easily do something else in parallel.

I'll try to do better analysis and some charts to visualize this ...

> Really the way to fix those two tests would be to rewrite them to not
> depend on the core regression tests.  The core tests do a lot of work
> that's not especially useful for the purposes of those tests, and it's
> not even clear that they are exercising all that we'd like to have
> exercised for those purposes.  In the case of 002_pg_upgrade, all
> we really need to do is create objects that will stress all of
> pg_dump.  It's a little harder to scope out what we want to test for
> 027_stream_regress, but it's still clear that the core tests do a lot
> of work that's not helpful.
> 

Perhaps, but that's a lot of work and time, and tricky - it seems we
might easily remove some useful test, even if it's not the original
purpose of that particular script.


regards

-- 
Tomas Vondra

On Mon, Sep 16, 2024 at 6:31 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Really the way to fix those two tests would be to rewrite them to not
> depend on the core regression tests.  The core tests do a lot of work
> that's not especially useful for the purposes of those tests, and it's
> not even clear that they are exercising all that we'd like to have
> exercised for those purposes.  In the case of 002_pg_upgrade, all
> we really need to do is create objects that will stress all of
> pg_dump.  It's a little harder to scope out what we want to test for
> 027_stream_regress, but it's still clear that the core tests do a lot
> of work that's not helpful.

027_stream_regress wants to get test coverage for the _redo routines
and replay subsystem, so I've wondered about defining a
src/test/regress/redo_schedule that removes what can be removed
without reducing _redo coverage.  For example, join_hash.sql must eat
a *lot* of valgrind CPU cycles, and contributes nothing to redo
testing.

Thinking along the same lines, 002_pg_upgrade wants to create database
objects to dump, so I was thinking you could have a dump_schedule that
removes anything that doesn't leave objects behind.  But you might be
right that it'd be better to start from scratch for that with that
goal in mind, and arguably also for the other.

(An interesting archeological detail about the regression tests is
that they seem to derive from the Wisconsin benchmark, famous for
benchmark wars and Oracle lawyers[1].  It seems quaint now that 'tenk'
was a lot of tuples, but I guess that Ingres on a PDP 11, which caused
offence by running that benchmark 5x faster, ran in something like
128kB of memory[2], so I can only guess the buffer pool must have been
something like 8 buffers or not much more in total?)

[1] https://jimgray.azurewebsites.net/BenchmarkHandbook/chapter4.pdf
[2] https://www.seas.upenn.edu/~zives/cis650/papers/INGRES.PDF

Thomas Munro <thomas.munro@gmail.com> writes:
> (An interesting archeological detail about the regression tests is
> that they seem to derive from the Wisconsin benchmark, famous for
> benchmark wars and Oracle lawyers[1].

This is quite off-topic for the thread, but ... we actually had an
implementation of the Wisconsin benchmark in src/test/bench, which
we eventually removed (a05a4b478).  It does look like the modern
regression tests borrowed the definitions of "tenk1" and some related
tables from there, but I think it'd be a stretch to say the tests
descended from it.

            regards, tom lane