On 1/11/21 12:36 AM, Tom Lane wrote:
=?utf-8?B?0JPQvtC70YPQsdC10LLQsCDQr9C90LA=?= <ish...@yandex.ru> writes:
Hello, I've found in source code that there is a function
satisfies_hash_partition(oid, modulus, remainder, column_values[]) which allows
to check if the certain column value will be placed in the certain partition.
I' d like to know if there is an opportunity not to check the certain partition
but to define which partition will be the certain column value placed in.
If you want to control what goes where, use list partitioning (or,
perhaps, range partitioning). Hash is only suitable if you do not
care which partition any particular row goes to.
Personally, I think hash partitioning is mostly academic, precisely
because of that. If the partitioning doesn't line up with application
requirements, you give up too much of the benefit of using partitions.
In non-MBCC systems, hash partitioning minimizes lock conflicts because the
writes aren't all going into the same page. OLTP systems can use this
feature to distribute writes across pages; some also allow for "mixed
pages", where records from multiple tables get written to the same page.
(This then means that one DIO is used to read a parent and all it's child
records. Naturally, range reports are *very* slow, but sometimes OLTP
performance is paramount.)
--
Angular momentum makes the world go 'round.
