Re: path toward faster partition pruning

From: David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>
To: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
Cc: Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Rajkumar Raghuwanshi <rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com>, Beena Emerson <memissemerson(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: path toward faster partition pruning
Date: 2017-11-07 02:14:51
Message-ID: CAKJS1f_EW9EvjSfvF3V4KWTN0F8C24oT3M97OXtb+FvLw2bWPA@mail.gmail.com
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On 7 November 2017 at 01:52, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
> Thanks. I'll look over it all again starting my Tuesday morning. (UTC+13)

I have a little more review to share:

1. Missing "in" in comment. Should be "mentioned in"

* get_append_rel_partitions
* Return the list of partitions of rel that pass the clauses mentioned
* rel->baserestrictinfo

2. Variable should be declared in inner scope with the following fragment:

void
set_basic_child_rel_properties(PlannerInfo *root,
RelOptInfo *rel,
RelOptInfo *childrel,
AppendRelInfo *appinfo)
{
AttrNumber attno;

if (rel->part_scheme)
{

which makes the code the same as where you moved it from.

3. Normally lfirst() is assigned to a variable at the start of a
foreach() loop. You have code which does not follow this.

foreach(lc, clauses)
{
Expr *clause;
int i;

if (IsA(lfirst(lc), RestrictInfo))
{
RestrictInfo *rinfo = lfirst(lc);

You could assign this to a Node * since the type is unknown to you at
the start of the loop.

4.
/*
* Useless if what we're thinking of as a constant is actually
* a Var coming from this relation.
*/
if (bms_is_member(rel->relid, constrelids))
continue;

should this be moved to just above the op_strict() test? This one seems cheaper.

5. Typo "paritions": /* No clauses to prune paritions, so scan all
partitions. */

But thinking about it more the comment should something more along the
lines of /* No useful clauses for partition pruning. Scan all
partitions. */

The key difference is that there might be clauses, just without Consts.

Actually, the more I look at get_append_rel_partitions() I think it
would be better if you re-shaped that if/else if test so that it only
performs the loop over the partindexes if it's been set.

I ended up with the attached version of the function after moving
things around a little bit.

I'm still reviewing but thought I'd share this part so far.

--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

Attachment Content-Type Size
get_append_rel_partitions.c text/x-csrc 2.0 KB

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