Обсуждение: printf ordering issues?

While using printf to do some good old fashioned print debugging, I
noticed that it seemed like my printf statements in the executor were
sometimes not getting printed to the log at all, and sometimes getting
printed out *before* the ones I have in the planner.

Upon further investigation I realized instead that the output from the
executor is getting flushed on the *subsequent* query.

Is there some kind of weird behavior that most hackers already know
about and I'm missing?

(Also I realize I can use elog(LOG...), but I'm still curious.)

Thanks,
James Coleman

James Coleman <jtc331@gmail.com> writes:
> While using printf to do some good old fashioned print debugging, I
> noticed that it seemed like my printf statements in the executor were
> sometimes not getting printed to the log at all, and sometimes getting
> printed out *before* the ones I have in the planner.

> Upon further investigation I realized instead that the output from the
> executor is getting flushed on the *subsequent* query.

> Is there some kind of weird behavior that most hackers already know
> about and I'm missing?

stdout is usually fully buffered, stderr usually is only line-buffered,
so if you print to stdout you need a lot of fflush'es to keep it in
sync with error/log messages (which go through stderr).  Personally
I've developed the habit of just making quick-log logging patches
print to stderr instead ...

            regards, tom lane