Re: range_agg

On Tue, Dec 8, 2020 at 3:00 AM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> On 2020-Dec-08, Alexander Korotkov wrote:
>
> > I also found a problem in multirange types naming logic.  Consider the
> > following example.
> >
> > create type a_multirange AS (x float, y float);
> > create type a as range(subtype=text, collation="C");
> > create table tbl (x __a_multirange);
> > drop type a_multirange;
> >
> > If you dump this database, the dump couldn't be restored.  The
> > multirange type is named __a_multirange, because the type named
> > a_multirange already exists.  However, it might appear that
> > a_multirange type is already deleted.  When the dump is restored, a
> > multirange type is named a_multirange, and the corresponding table
> > fails to be created.  The same thing doesn't happen with arrays,
> > because arrays are not referenced in dumps by their internal names.
> >
> > I think we probably should add an option to specify multirange type
> > names while creating a range type.  Then dump can contain exact type
> > names used in the database, and restore wouldn't have a names
> > collision.
>
> Hmm, good point.  I agree that a dump must preserve the name, since once
> created it is user-visible.  I had not noticed this problem, but it's
> obvious in retrospect.
>
> > In general, I wonder if we can make the binary format of multiranges
> > more efficient.  It seems that every function involving multiranges
> > from multirange_deserialize().  I think we can make functions like
> > multirange_contains_elem() much more efficient.  Multirange is
> > basically an array of ranges.  So we can pack it as follows.
> > 1. Typeid and rangecount
> > 2. Tightly packed array of flags (1-byte for each range)
> > 3. Array of indexes of boundaries (4-byte for each range).  Or even
> > better we can combine offsets and lengths to be compression-friendly
> > like jsonb JEntry's do.
> > 4. Boundary values
> > Using this format, we can implement multirange_contains_elem(),
> > multirange_contains_range() without deserialization and using binary
> > search.  That would be much more efficient.  What do you think?
>
> I also agree.  I spent some time staring at the I/O code a couple of
> months back but was unable to focus on it for long enough.  I don't know
> JEntry's format, but I do remember that the storage format for JSONB was
> widely discussed back then; it seems wise to apply similar logic or at
> least similar reasoning.

Thank you for your feedback!

I'd like to publish my revision of the patch.  So Paul could start
from it.  The changes I made are minor
1. Add missing types to typedefs.list
2. Run pg_indent run over the changed files and some other formatting changes
3. Reorder the regression tests to evade the error spotted by
commitfest.cputube.org

I'm switching this patch to WOA.

------
Regards,
Alexander Korotkov