Thread: Misleading comment in tuplesort_set_bound
While digging into the incremental sort patch, I noticed in
tuplesort.c at the beginning of the function in $SUBJECT we have this
comment and assertion:
tuplesort_set_bound(Tuplesortstate *state, int64 bound)
{
/* Assert we're called before loading any tuples */
Assert(state->status == TSS_INITIAL);
But AFAICT from reading the code in puttuple_common the state remains
TSS_INITIAL while tuples are inserted (unless we reach a point where
we decide to transition it to TSS_BOUNDED or TSS_BUILDRUNS).
Therefore it's not true that the assertion guards against having
loaded any tuples; rather it guarantees that we remain in standard
memory quicksort mode.
Assuming my understanding is correct, I've attached a small patch to
update the comment to "Assert we're still in memory quicksort mode and
haven't transitioned to heap or tape mode".
Note: this also means the function header comment "Must be called
before inserting any tuples" is a condition that isn't actually
validated, but I think that's fine given it's not a new problem and
even more so since the same comment goes on to say that that's
probably not a strict requirement.
James Coleman
Attachment
James Coleman <jtc331@gmail.com> writes:
> While digging into the incremental sort patch, I noticed in
> tuplesort.c at the beginning of the function in $SUBJECT we have this
> comment and assertion:
> tuplesort_set_bound(Tuplesortstate *state, int64 bound)
> {
> /* Assert we're called before loading any tuples */
> Assert(state->status == TSS_INITIAL);
> But AFAICT from reading the code in puttuple_common the state remains
> TSS_INITIAL while tuples are inserted (unless we reach a point where
> we decide to transition it to TSS_BOUNDED or TSS_BUILDRUNS).
You missed the relevance of the next line:
Assert(state->memtupcount == 0);
I think the comment is fine as-is. Perhaps the code would be clearer
though, if we merged those two asserts into one?
/* Assert we're called before loading any tuples */
Assert(state->status == TSS_INITIAL &&
state->memtupcount == 0);
I'm not totally sure about the usefulness/relevance of the two
assertions following these, but they could likely do with their
own comment(s), because this one surely isn't covering them.
regards, tom lane
On 2019-Aug-26, Tom Lane wrote: > James Coleman <jtc331@gmail.com> writes: > I think the comment is fine as-is. Perhaps the code would be clearer > though, if we merged those two asserts into one? > > /* Assert we're called before loading any tuples */ > Assert(state->status == TSS_INITIAL && > state->memtupcount == 0); Makes sense to me. James, do you want to submit a new patch? > I'm not totally sure about the usefulness/relevance of the two > assertions following these, but they could likely do with their > own comment(s), because this one surely isn't covering them. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Yes, planning on it, just a bit behind right now so will likely be a few more days at least. On Thu, Sep 5, 2019 at 4:57 PM Alvaro Herrera from 2ndQuadrant <alvherre@alvh.no-ip.org> wrote: > > On 2019-Aug-26, Tom Lane wrote: > > > James Coleman <jtc331@gmail.com> writes: > > > I think the comment is fine as-is. Perhaps the code would be clearer > > though, if we merged those two asserts into one? > > > > /* Assert we're called before loading any tuples */ > > Assert(state->status == TSS_INITIAL && > > state->memtupcount == 0); > > Makes sense to me. James, do you want to submit a new patch? > > > I'm not totally sure about the usefulness/relevance of the two > > assertions following these, but they could likely do with their > > own comment(s), because this one surely isn't covering them. > > > -- > Álvaro Herrera https://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
On 2019-Sep-05, James Coleman wrote: > Yes, planning on it, just a bit behind right now so will likely be a > few more days at least. [ shrug ] It seemed to require no further work, so I just pushed Tom's proposed change. I added an empty line after the new combined assertion, which makes clearer (to me anyway) that the other assertions are unrelated. Thanks -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> [ shrug ] It seemed to require no further work, so I just pushed Tom's
> proposed change.
> I added an empty line after the new combined assertion, which makes
> clearer (to me anyway) that the other assertions are unrelated.
Actually, the thing I wanted to add was some actual comments for
those other assertions. But that requires a bit of research that
I hadn't made time for...
regards, tom lane