Re: Adding support for Default partition in partitioning

Hi,

On Mon, Jun 19, 2017 at 12:34 PM, Amit Langote <
Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:

> On 2017/06/16 14:16, Ashutosh Bapat wrote:
> > On Fri, Jun 16, 2017 at 12:48 AM, Robert Haas <robertmhaas(at)gmail(dot)com>
> wrote:
> >> On Thu, Jun 15, 2017 at 12:54 PM, Ashutosh Bapat
> >> <ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
> >>> Some more comments on the latest set of patches.
> >> or looking up the OID in the
> >> relcache multiple times.
> >
> > I am not able to understand this in the context of default partition.
> > After that nobody else is going to change its partitions and their
> > bounds (since both of those require heap_open on parent which would be
> > stuck on the lock we hold.). So, we have to check only once if the
> > table has a default partition. If it doesn't, it's not going to
> > acquire one unless we release the lock on the parent i.e at the end of
> > transaction. If it has one, it's not going to get dropped till the end
> > of the transaction for the same reason. I don't see where we are
> > looking up OIDs multiple times.
>
> Without heap_opening the parent, the only way is to look up parentOid's
> children in pg_inherits and for each child looking up its pg_class tuple
> in the syscache to see if its relpartbound indicates that it's a default
> partition. That seems like it won't be inexpensive either.
>
> It would be nice if could get that information (that is - is a given
> relation being heap_drop_with_catalog'd a partition of the parent that
> happens to have default partition) in less number of steps than that.
> Having that information in relcache is one way, but as mentioned, that
> turns out be expensive.
>
> Has anyone considered the idea of putting the default partition OID in the
> pg_partitioned_table catalog? Looking the above information up would
> amount to one syscache lookup. Default partition seems to be special
> enough object to receive a place in the pg_partitioned_table tuple of the
> parent. Thoughts?
>

I liked this suggestion. Having an entry in pg_partitioned_table would avoid
both expensive methods, i.e. 1. opening the parent or 2. lookup for
each of the children first in pg_inherits and then its corresponding entry
in
pg_class.
Unless anybody has any other suggestions/comments here, I am going to
implement this suggestion.

Thanks,
Jeevan Ladhe