Re: path toward faster partition pruning

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: Dilip Kumar <dilipbalaut(at)gmail(dot)com>
Cc: Rajkumar Raghuwanshi <rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com>, Beena Emerson <memissemerson(at)gmail(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: path toward faster partition pruning
Date: 2017-10-31 08:43:51
Message-ID: fb89b3b2-d42c-48ad-64c5-b0292e1ad0d0@lab.ntt.co.jp
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Thanks Dilip for reviewing.

On 2017/10/31 1:50, Dilip Kumar wrote:
> On Mon, Oct 30, 2017 at 12:20 PM, Amit Langote
> <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> On 2017/10/30 14:55, Amit Langote wrote:
>>> Fixed in the attached updated patch, along with a new test in 0001 to
>>> cover this case. Also, made a few tweaks to 0003 and 0005 (moved some
>>> code from the former to the latter) around the handling of ScalarArrayOpExprs.
>>
>> Sorry, I'd forgotten to include some changes.
>>
>> In the previous versions, RT index of the table needed to be passed to
>> partition.c, which I realized is no longer needed, so I removed that
>> requirement from the interface. As a result, patches 0002 and 0003 have
>> changed in this version.
>
> Some Minor comments:
>
> + * get_rel_partitions
> + * Return the list of partitions of rel that pass the clauses mentioned
> + * rel->baserestrictinfo
> + *
> + * Returned list contains the AppendRelInfos of chosen partitions.
> + */
> +static List *
> +get_append_rel_partitions(PlannerInfo *root,
>
> Function name in function header is not correct.

Fixed.

> + !DatumGetBool(((Const *) clause)->constvalue))
> + {
> + *constfalse = true;
> + continue;
>
> DatumGetBool will return true if the first byte of constvalue is
> nonzero otherwise
> false. IIUC, this is not the intention here. Or I am missing something?

This coding pattern is in use in quite a few places; see for example in
restriction_is_constant_false() and many others like
relation_excluded_by_constraints(), negate_clause(), etc.

If a RestrictInfo is marked pseudoconstant=true, then the clause therein
must be a Const with constvalue computing to 0 if the clause is false, so
that DatumGetBool(constvalue) returns boolean false and non-zero otherwise.

> + * clauses in this function ourselves, for example, having both a > 1 and
> + * a = 0 the list
>
> a = 0 the list -> a = 0 in the list

Right, fixed.

>
> +static bool
> +partkey_datum_from_expr(const Expr *expr, Datum *value)
> +{
> + /*
> + * Add more expression types here as needed to support higher-level
> + * code.
> + */
> + switch (nodeTag(expr))
> + {
> + case T_Const:
> + *value = ((Const *) expr)->constvalue;
> + return true;
>
> I think for evaluating other expressions (e.g. T_Param) we will have
> to pass ExprContext to this function.

That's right.

> Or we can do something cleaner
> because if we want to access the ExprContext inside
> partkey_datum_from_expr then we may need to pass it to
> "get_partitions_from_clauses" which is a common function for optimizer
> and executor.

Yeah, I've thought about that a little. Since nothing else but the
planner calls it now and the planner doesn't itself have its hands on the
ExprContext that would be necessary for computing something like Params, I
left it out of the interface for now. That said, I *am* actually thinking
about some interface changes that would be necessary for some other
unrelated functionality/optimizations that callers like the run-time
pruning code would expect of get_partitions_from_clauses(). We can design
the interface extension such that the aforementioned ExprContext is passed
together.

Attached updated version of the patches addressing some of your comments
above and fixing a bug that Rajkumar reported [1]. As mentioned there,
I'm including here a patch (the 0005 of the attached) to tweak the default
range partition constraint to be explicit about null values that it might
contain. So, there are 6 patches now and what used to be patch 0005 in
the previous set is patch 0006 in this version of the set.

Thanks,
Amit

[1]
https://www.postgresql.org/message-id/cd5a2d2e-0957-042c-40c2-06033fe0abf2@lab.ntt.co.jp

Attachment Content-Type Size
0001-Add-new-tests-for-partition-pruning-v9.patch text/plain 47.2 KB
0002-Planner-side-changes-for-partition-pruning-v9.patch text/plain 37.3 KB
0003-Implement-get_partitions_from_clauses-v9.patch text/plain 33.5 KB
0004-Some-interface-changes-for-partition_bound_-cmp-bsea-v9.patch text/plain 10.1 KB
0005-Tweak-default-range-partition-s-constraint-a-little-v9.patch text/plain 2.9 KB
0006-Implement-get_partitions_for_keys-v9.patch text/plain 21.4 KB

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