| 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>, Anastasia Lubennikova <lubennikovaav(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Rahila Syed <rahilasyed(dot)90(at)gmail(dot)com> |
| Subject: | Re: Parallel Index Scans |
| Date: | 2017-02-14 17:48:08 |
| Message-ID: | CA+TgmoZxdAT72VAG90A-RKOFLLCOwL9xEbz-aOOhM4VhjmBxzw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Feb 13, 2017 at 9:04 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> I think the comment at that place is not as clear as it should be. So
> how about changing it as below:
>
> Existing comment:
> --------------------------
> /*
> * For parallel scans, get the last page scanned as it is quite
> * possible that by the time we try to fetch previous page, other
> * worker has also decided to scan that previous page. So we
> * can't rely on _bt_walk_left call.
> */
>
> Modified comment:
> --------------------------
> /*
> * For parallel scans, it is quite possible that by the time we try to fetch
> * the previous page, another worker has also decided to scan that
> * previous page. So to avoid that we need to get the last page scanned
> * from shared scan descriptor before calling _bt_walk_left.
> */
That sounds way better.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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