On Fri, Jun 19, 2020, 5:45 PM Amul Sul <sula...@gmail.com> wrote: > On Fri, Jun 19, 2020 at 3:50 PM Srinivasa T N <seen...@gmail.com> wrote: > > > > > > > > On Fri, Jun 19, 2020 at 3:09 PM Amul Sul <sula...@gmail.com> wrote: > >> > >> On Fri, Jun 19, 2020 at 1:28 PM Srinivasa T N <seen...@gmail.com> > wrote: > >> > > >> > On Fri, Jun 19, 2020 at 12:34 PM Laurenz Albe < > laurenz.a...@cybertec.at> wrote: > >> >> > >> >> On Fri, 2020-06-19 at 12:12 +0530, Srinivasa T N wrote: > >> >> > On Fri, Jun 19, 2020 at 11:44 AM David Rowley < > dgrowle...@gmail.com> wrote: > >> >> > > On Fri, 19 Jun 2020 at 17:42, Srinivasa T N <seen...@gmail.com> > wrote: > >> >> > > > After seeing the below, I feel partitioning is not working > properly or it maybe case that my understanding is wrong. Can somebody > explain me what is happening? > >> >> > > > >> >> > > It's your understanding that's not correct. The value of is > passed > >> >> > > through a hash function and the partition is selected based > partition > >> >> > > matching the remainder value after dividing the return value of > the > >> >> > > hash function by the largest modulus of any partition. > >> >> > > > >> >> > > That might surprise you, but how would you select which > partition a > >> >> > > varchar value should go into if you didn't use a hash function. > >> >> > > > >> >> > > David > >> >> > > >> >> > How can I see the output of hash function that is used internally? > >> >> > >> >> In the case of "integer", the hash function is > "pg_catalog"."hashint4". > >> >> > >> >> Yours, > >> >> Laurenz Albe > >> >> -- > >> >> Cybertec | https://www.cybertec-postgresql.com > >> >> > >> > I guess output formatting is wrong, any help? > >> > > >> > postgres=# select pg_catalog.hashint4(7); > >> > hashint4 > >> > ------------ > >> > -978793473 > >> > (1 row) > >> > > >> Instead of direct hash function, the easiest way to use > >> satisfies_hash_partition() what is used in defining hash > >> partitioning constraint. > >> > >> You can see the partition constraint by description partition table i.e. > >> use \d+ busbar_version5. > >> > >> Regards, > >> Amul > > > > > > Sorry, I did not get you. > > > > My current \d+ is > > > > postgres=# \d+ busbar_version6; > > Table "test.busbar_version6" > > Column | Type | Collation | Nullable | Default | Storage | Stats > target | > > Description > > > ----------+---------+-----------+----------+---------+---------+--------------+- > > ------------ > > objectid | integer | | | | plain | > | > > ver_id | integer | | | | plain | > | > > Partition of: busbar_version FOR VALUES WITH (modulus 10, remainder 6) > > Partition constraint: satisfies_hash_partition('16397'::oid, 10, 6, > ver_id) > > Access method: heap > > > By executing "SELECT satisfies_hash_partition('16397'::oid, 10, 6, > <VALUE>) " > will tell you whether <VALUE> fits in the partition having modulus 10 and > remainder 6 or not. > > Regards, > Amul >
OK.. Thanks. BTW, is it possible to have a custom hash function instead of predefined hash function? Regards, Seenu. >
