Horton

Re: [HACKERS] Runtime Partition Pruning

Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>

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From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
To: Andy Fan <zhihui.fan1213@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Beena Emerson <memissemerson@gmail.com>, Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>, amul sul <sulamul@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Dilip Kumar <dilipbalaut@gmail.com>, Amit Langote <amitlangote09@gmail.com>, David Rowley <dgrowleyml@gmail.com>
Date: 2020-10-12T09:47:50Z
Lists: pgsql-hackers 
On Mon, Oct 12, 2020 at 7:59 AM Andy Fan <zhihui.fan1213@gmail.com> wrote:

>
> Sorry for the late reply!  Suppose we have partition defined like this:
> p
> - p1
> - p2
>
> When you talk about "the statistics from the partitioned table", do you
> mean the statistics from p or p1/p2?   I just confirmed there is no statistics
> for p (at least pg_class.reltuples = -1),  so I think you are talking about
> p1/p2.

I am talking about p when I say statistics from the partitioned table.
I see that pg_statistic row from p is well populated.
pg_class.reltuples = -1 indicates that the heap doesn't have any rows.
set_rel_size() sets the number of rows in the partitioned table based
on the rows in individual unpruned partitions.

>
> Here we are talking about partkey = $1 or  partkey = RunTimeValue.
> so even the value can hit 1 partition only,  but since we don't know
> the exact value, so we treat all the partition equally.  so looks
> nothing wrong with partition level estimation.  However when we cost
> the Append path, we need know just one of them can be hit,  then
> we need do something there.  Both AppendPath->rows/total_cost
> should be adjusted (That doesn't happen now).

I think in this case we can safely assume that only one partition will
remain so normalize costs considering that only one partition will
survive.

-- 
Best Wishes,
Ashutosh Bapat

Commits

  1. Initialize ExprStates once in run-time partition pruning

  2. Add bms_prev_member function

  3. Support partition pruning at execution time

  4. Document partprune.c a little better

  5. Fix crash in pg_replication_slot_advance

  6. Add parallel-aware hash joins.

  7. Fix typo.

  8. Allow --with-bonjour to work with non-macOS implementations of Bonjour.

  9. Mention need for --no-inc-recursive in rsync command