Re: ALTER INDEX .. SET STATISTICS ... behaviour

From: Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: ALTER INDEX .. SET STATISTICS ... behaviour
Date: 2017-08-30 12:26:36
Message-ID: CAPpHfdv4PvsvF85mugD6oL+y_VcXpdzUb8VikX6YyrST-hdnow@mail.gmail.com
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On Thu, Jun 1, 2017 at 4:10 PM, Alexander Korotkov <
a(dot)korotkov(at)postgrespro(dot)ru> wrote:

> On Wed, May 31, 2017 at 7:18 PM, Alexander Korotkov <
> a(dot)korotkov(at)postgrespro(dot)ru> wrote:
>
>> On Wed, May 31, 2017 at 6:53 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>
>>> Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> writes:
>>> > I've discovered that PostgreSQL is able to run following kind of
>>> queries in
>>> > order to change statistic-gathering target for an indexed expression.
>>>
>>> > ALTER INDEX index_name ALTER COLUMN expr SET STATISTICS stat_target;
>>>
>>> > It's been previously discussed in [1].
>>>
>>> > I think this should be fixed not just in docs. This is why I've
>>> started
>>> > thread in pgsql-hackers. For me usage of internal column names "expr",
>>> > "expr1", "expr2" etc. looks weird. And I think we should replace it
>>> with a
>>> > better syntax. What do you think about these options?
>>>
>>> > ALTER INDEX index_name ALTER EXPRESSION 0 SET STATISTICS stat_target;
>>> --
>>> > Refer expression by its number
>>> > ALTER INDEX index_name ALTER EXPRESSION (x + y) SET STATISTICS
>>> stat_target;
>>> > -- Refer expression by its definition
>>>
>>> Don't like either of those particularly, but what about just targeting
>>> a column by column number, independently of whether it's an expression?
>>>
>>> ALTER INDEX myindex ALTER COLUMN 4 SET STATISTICS 1000;
>>>
>>
>> I completely agree with that.
>> If no objections, I will write a patch for that.
>>
>
> Please, find it in attached patch.
>
> I decided to forbid referencing columns by numbers for tables, because
> those numbers could contain gaps. Also, I forbid altering statistics
> target for non-expression index columns, because it has no effect.
>

Patch rebased to current master is attached.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Attachment Content-Type Size
alter-index-statistics-2.patch application/octet-stream 17.2 KB

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