printf ordering issues?

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