Re: On partitioning

On Sat, Dec 6, 2014 at 3:06 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> Sure, I don't feel we should not provide anyway to take dump
> for individual partition but not at level of independent table.
> May be something like --table <table_name>
> --partition <partition_name>.
>
> In general, I think we should try to avoid exposing that partitions are
> individual tables as that might hinder any future enhancement in that
> area (example if we someone finds a different and better way to
> arrange the partition data, then due to the currently exposed syntax,
> we might feel blocked).

I guess I'm in disagreement with you - and, perhaps - the majority on
this point. I think that ship has already sailed: partitions ARE
tables. We can try to make it less necessary for users to ever look
at those tables as separate objects, and I think that's a good idea.
But trying to go from a system where partitions are tables, which is
what we have today, to a system where they are not seems like a bad
idea to me. If we make a major break from how things work today,
we're going to end up having to reimplement stuff that already works.

Besides, I haven't really seen anyone propose something that sounds
like a credible alternative. If we could make partition objects
things that the storage layer needs to know about but the query
planner doesn't need to understand, that'd be maybe worth considering.
But I don't see any way that that's remotely feasible. There are lots
of places that we assume that a heap consists of blocks number 0 up
through N: CTID pointers, index-to-heap pointers, nodeSeqScan, bits
and pieces of the way index vacuuming is handled, which in turn bleeds
into Hot Standby. You can't just decide that now block numbers are
going to be replaced by some more complex structure, or even that
they're now going to be nonlinear, without breaking a huge amount of
stuff.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company