| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | Anastasia Lubennikova <a(dot)lubennikova(at)postgrespro(dot)ru>, Andrey Borodin <amborodin(at)acm(dot)org>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Anastasia Lubennikova <lubennikovaav(at)gmail(dot)com> |
| Subject: | Re: WIP: Covering + unique indexes. |
| Date: | 2016-10-05 16:59:41 |
| Message-ID: | CA+TgmobfBMJE6H_L9rcw43h+MOE0nCScY_5n7cdWeE49BKTafw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Oct 5, 2016 at 9:04 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> Okay, but in that case I think we don't need to store including
> columns in non-leaf pages to get the exact ordering. As mentioned
> upthread, we can use truncated scan key to reach to leaf level and
> then use the complete key to find the exact location to store the key.
> This is only possible if there exists an opclass for columns that are
> covered as part of including clause. So, we can allow "order by" to
> use index scan only if the columns covered in included clause have
> opclass for btree.
But what if there are many pages full of keys that have the same
values for the non-INCLUDING columns?
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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