| From: | Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Stark <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
| Subject: | Re: Freeze avoidance of very large table. |
| Date: | 2015-07-13 14:48:02 |
| Message-ID: | CAD21AoA9KD-pQtcNdr7HFSf_droT_sWqSTgU4KKnVBUFbOVFNg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Jul 13, 2015 at 9:22 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2015-07-13 21:03:07 +0900, Sawada Masahiko wrote:
>> Even If we implement rewriting tool for vm into pg_upgrade, it will
>> take time as much as revacuum because it need whole scanning table.
>
> Why would it? Sure, you can only set allvisible and not the frozen bit,
> but that's fine. That way the cost for freezing can be paid over time.
>
> If we require terrabytes of data to be scanned, including possibly
> rewriting large portions due to freezing, before index only scans work
> and most vacuums act in a partial manner the migration to 9.6 will be a
> major pain for our users.
Ah, If we set all bit as not all-frozen, we don't need to whole table
scanning, only scan vm.
And I agree with this.
But please image the case where old cluster has table which is very
large, read-only and vacuum freeze is done.
In this case, the all-frozen bit of such table in new cluster will not
set, unless we do vacuum freeze again.
The information of all-frozen of such table is lacked.
Regards,
--
Masahiko Sawada
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