| From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
|---|---|
| To: | Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Advance xmin aggressively on Read Commit isolation level |
| Date: | 2020-11-06 08:53:45 |
| Message-ID: | CA+hUKGLMY8h5ZWHBgsTY8ECG2vFWtCHCdQrra_X+WwKiSV-ZGQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Nov 6, 2020 at 9:48 PM Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> wrote:
> I have 2 ideas about this. One is in the Read Committed level, we can advance xmin
> aggressively. suppose it started at t1, and complete a query at t2. the xmin should
> be t1 currently. Can we advance the xmin to t2 since it is read committed level,
> The data older than t2 will never be used? Another one is can we force to clean
> up the old tuples which are older than xxx? If users want to access that,
> we can just raise errors. Oracle uses this strategy and the error code is
> ORA-01555.
Hi Andy,
For the second idea, we have old_snapshot_threshold which does exactly
that since 9.6. There have been some questions about whether it works
correctly, though: see https://commitfest.postgresql.org/30/2682/ if
you would like to help look into that :-)
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