| From: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
|---|---|
| To: | Peter Geoghegan <pg(at)bowt(dot)ie>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Andrey Borodin <x4mmm(at)yandex-team(dot)ru>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Darafei Komяpa Praliaskouski <me(at)komzpa(dot)net>, Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Yet another fast GiST build |
| Date: | 2021-01-17 22:52:12 |
| Message-ID: | 5678c114-c298-ac70-8fba-8bd5c87b048a@iki.fi |
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| Lists: | pgsql-hackers |
On 18/01/2021 00:35, Peter Geoghegan wrote:
> On Sun, Jan 17, 2021 at 12:50 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I noticed that gist_page_items() thinks it can hold inter_call_data->rel
>> open across a series of calls. That's completely unsafe: the executor
>> might not run the call series to completion (see LIMIT), resulting in
>> relcache leak complaints.
Fixed, thanks! I changed it to return a tuplestore.
> It also has the potential to run into big problems should the user
> input a raw page image with an regclass-argument-incompatible tuple
> descriptor. Maybe that's okay (this is a tool for experts), but it
> certainly is a consideration.
I'm not sure I understand. It's true that the raw page image can contain
data from a different index, or any garbage really. And the function
will behave badly if you do that. That's an accepted risk with
pageinspect functions, that's why they're superuser-only, although some
of them are more tolerant of corrupt pages than others. The
gist_page_items_bytea() variant doesn't try to parse the key data and is
less likely to crash on bad input.
- Heikki
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