On Fri, Jun 19, 2020 at 3:50 PM Srinivasa T N <seenutn@xxxxxxxxx> wrote: > > > > On Fri, Jun 19, 2020 at 3:09 PM Amul Sul <sulamul@xxxxxxxxx> wrote: >> >> On Fri, Jun 19, 2020 at 1:28 PM Srinivasa T N <seenutn@xxxxxxxxx> wrote: >> > >> > On Fri, Jun 19, 2020 at 12:34 PM Laurenz Albe <laurenz.albe@xxxxxxxxxxx> 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 <dgrowleyml@xxxxxxxxx> wrote: >> >> > > On Fri, 19 Jun 2020 at 17:42, Srinivasa T N <seenutn@xxxxxxxxx> 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
