Обсуждение: Passing CopyMultiInsertInfo structure to CopyMultiInsertInfoNextFreeSlot()

On Mon, 13 May 2019 at 23:20, Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
> In the latest PostgreSQL code, I could see that we are passing CopyMultiInsertInfo structure to
CopyMultiInsertInfoNextFreeSlot()although it is not being used anywhere in that function. Could you please let me know
ifit has been done intentionally or it is just an overlook that needs to be corrected. AFAIU,
CopyMultiInsertInfoNextFreeSlot()is just intended to return the next free slot available in the multi insert buffer and
wealready have that buffer stored in ResultRelInfo structure which is also being passed to that function so not sure
whatcould be the purpose of passing CopyMultiInsertInfo structure as well. Please let me know if i am missing something
here.Thank you. 

There's likely no good reason for that. The attached removes it.

--
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

On Mon, May 13, 2019 at 08:17:49PM +0530, Ashutosh Sharma wrote:
> Thanks for the confirmation David. The patch looks good to me.

It looks to me that it can be a matter a consistency with the other
APIs dealing with multi-inserts in COPY.  For now I have added an open
item on that.
--
Michael

On Tue, 14 May 2019 at 13:00, Michael Paquier <michael@paquier.xyz> wrote:
>
> On Mon, May 13, 2019 at 08:17:49PM +0530, Ashutosh Sharma wrote:
> > Thanks for the confirmation David. The patch looks good to me.
>
> It looks to me that it can be a matter a consistency with the other
> APIs dealing with multi-inserts in COPY.  For now I have added an open
> item on that.

When I wrote the code I admit that I was probably wearing my
object-orientated programming hat. I had in mind that the whole
function series would have made a good class.  Passing the
CopyMultiInsertInfo was sort of the non-OOP equivalent to having
this/Me/self available, as it would be for any instance method of a
class.  Back to reality, this isn't OOP, so I was wearing the wrong
hat.  I think the unused parameter should likely be removed.  It's
probably not doing a great deal of harm since the function is static
inline and the compiler should be producing any code for the unused
param, but for the sake of preventing confusion, it should be removed.
Ashutosh had to ask about it, so it wasn't immediately clear what the
purpose of it was. Since there's none, be gone with it, I say.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

On Tue, May 14, 2019 at 01:19:30PM +1200, David Rowley wrote:
> When I wrote the code I admit that I was probably wearing my
> object-orientated programming hat. I had in mind that the whole
> function series would have made a good class.  Passing the
> CopyMultiInsertInfo was sort of the non-OOP equivalent to having
> this/Me/self available, as it would be for any instance method of a
> class.  Back to reality, this isn't OOP, so I was wearing the wrong
> hat.  I think the unused parameter should likely be removed.  It's
> probably not doing a great deal of harm since the function is static
> inline and the compiler should be producing any code for the unused
> param, but for the sake of preventing confusion, it should be removed.
> Ashutosh had to ask about it, so it wasn't immediately clear what the
> purpose of it was. Since there's none, be gone with it, I say.

Sounds fair to me.  This has been introduced by 86b8504, so let's see
what's Andres take.
--
Michael

On 2019-May-14, Michael Paquier wrote:

> On Tue, May 14, 2019 at 01:19:30PM +1200, David Rowley wrote:
> > When I wrote the code I admit that I was probably wearing my
> > object-orientated programming hat. I had in mind that the whole
> > function series would have made a good class.  Passing the
> > CopyMultiInsertInfo was sort of the non-OOP equivalent to having
> > this/Me/self available, as it would be for any instance method of a
> > class.  Back to reality, this isn't OOP, so I was wearing the wrong
> > hat.  I think the unused parameter should likely be removed.  It's
> > probably not doing a great deal of harm since the function is static
> > inline and the compiler should be producing any code for the unused
> > param, but for the sake of preventing confusion, it should be removed.
> > Ashutosh had to ask about it, so it wasn't immediately clear what the
> > purpose of it was. Since there's none, be gone with it, I say.
> 
> Sounds fair to me.  This has been introduced by 86b8504, so let's see
> what's Andres take.

If this were up to me, I'd leave the function signature alone, and just add
    (void) miinfo;        /* unused parameter */
to the function code.  It seems perfectly reasonable to have that
function argument, and a little weird not to have it.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

On 2019-05-17 11:09:41 +0530, Ashutosh Sharma wrote:
> On Fri, May 17, 2019 at 3:10 AM Alvaro Herrera <alvherre@2ndquadrant.com>
> wrote:
> 
> > On 2019-May-14, Michael Paquier wrote:
> >
> > > On Tue, May 14, 2019 at 01:19:30PM +1200, David Rowley wrote:
> > > > When I wrote the code I admit that I was probably wearing my
> > > > object-orientated programming hat. I had in mind that the whole
> > > > function series would have made a good class.  Passing the
> > > > CopyMultiInsertInfo was sort of the non-OOP equivalent to having
> > > > this/Me/self available, as it would be for any instance method of a
> > > > class.  Back to reality, this isn't OOP, so I was wearing the wrong
> > > > hat.  I think the unused parameter should likely be removed.  It's
> > > > probably not doing a great deal of harm since the function is static
> > > > inline and the compiler should be producing any code for the unused
> > > > param, but for the sake of preventing confusion, it should be removed.
> > > > Ashutosh had to ask about it, so it wasn't immediately clear what the
> > > > purpose of it was. Since there's none, be gone with it, I say.
> > >
> > > Sounds fair to me.  This has been introduced by 86b8504, so let's see
> > > what's Andres take.
> >
> > If this were up to me, I'd leave the function signature alone, and just add
> >         (void) miinfo;          /* unused parameter */
> > to the function code.  It seems perfectly reasonable to have that
> > function argument, and a little weird not to have it.

I'd do that, or simply nothing. We've plenty of unused args, so I don't
see much point in these kind of "unused parameter" warning suppressions
in isolated places.


> I think, we should only do that if at all there is any circumstances under
> which 'miinfo' might be used otherwise it would good to remove it unless
> there is some specific reason for having it.

It seems like it could entirely be reasonable to e.g. reuse slots across
partitions, which'd require CopyMultiInsertInfo to be around.

Also, from a consistency point, it seems the caller doesn't need to know
whether all the necessary information is in the ResultRelInfo and not in
CopyMultiInsertInfo for *some* of the CopyMultiInsertInfo functions.

Greetings,

Andres Freund

Hi,

On 2019-05-18 06:14:15 +0530, Ashutosh Sharma wrote:
> On Sat, May 18, 2019 at 1:34 AM Andres Freund <andres@anarazel.de> wrote:
> Considering that we can have MAX_BUFFERED_TUPLES slots in each multi-insert
> buffer and we do flush the buffer after MAX_BUFFERED_TUPLES tuples have
> been stored, it seems unlikely that we would ever come across a situation
> where one partition would need to reuse the slot of another partition.

I don't think this is right. Obviously it'd not be without a bit more
changes, but we definitely *should* try to reuse slots from other
partitions (including the root partition if compatible). Creating them
isn't that cheap, compared to putting slots onto a freelist for a wihle.


> Also, from a consistency point, it seems the caller doesn't need to know
> > whether all the necessary information is in the ResultRelInfo and not in
> > CopyMultiInsertInfo for *some* of the CopyMultiInsertInfo functions.
> >
> >
> I actually feel that the function name itself is not correct here, it
> appears to be confusing and inconsistent considering the kind of work that
> it is doing. I think, the function name should have been CopyMultiInsert
> *Buffer*NextFreeSlot() instead of CopyMultiInsert*Info*NextFreeSlot(). What
> do you think, Andres, David, Alvaro ?

Unless somebody else presses back hard against doing so *soon*, I'm
going to close this open issue. I don't think it's worth spending
further time arguing about a few characters.

Greetings,

Andres Freund

On Sat, 18 May 2019 at 12:49, Andres Freund <andres@anarazel.de> wrote:
>
> On 2019-05-18 06:14:15 +0530, Ashutosh Sharma wrote:
> > I actually feel that the function name itself is not correct here, it
> > appears to be confusing and inconsistent considering the kind of work that
> > it is doing. I think, the function name should have been CopyMultiInsert
> > *Buffer*NextFreeSlot() instead of CopyMultiInsert*Info*NextFreeSlot(). What
> > do you think, Andres, David, Alvaro ?
>
> Unless somebody else presses back hard against doing so *soon*, I'm
> going to close this open issue. I don't think it's worth spending
> further time arguing about a few characters.

I'd say if we're not going to bother removing the unused param that
there's not much point in renaming the function. The proposed name
might make sense if the function was:

static inline TupleTableSlot *
CopyMultiInsertBufferNextFreeSlot(CopyMultiInsertBuffer *buffer, Relation rel)

then that might be worth a commit, but giving it that name without
changing the signature to that does not seem like an improvement to
me.

I'm personally about +0.1 for making the above change, which is well
below my threshold for shouting and screaming.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

David Rowley <david.rowley@2ndquadrant.com> writes:
> On Sat, 18 May 2019 at 12:49, Andres Freund <andres@anarazel.de> wrote:
>> Unless somebody else presses back hard against doing so *soon*, I'm
>> going to close this open issue. I don't think it's worth spending
>> further time arguing about a few characters.

> I'd say if we're not going to bother removing the unused param that
> there's not much point in renaming the function.

FWIW, I'm on the side of "we shouldn't change this".  There's lots of
unused parameters in PG functions, and in most of those cases the API
is reasonable as it stands.

            regards, tom lane