| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Amit Kapila <amit(dot)kapila(at)huawei(dot)com>, PG Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Regarding Checkpoint Redo Record |
| Date: | 2012-01-04 18:00:06 |
| Message-ID: | CA+Tgmoa4GGiUFW+SvDhqXzGjN-xLcSpMJyXBONVt58tGDPOrcg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Jan 4, 2012 at 11:02 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On Wed, Jan 4, 2012 at 3:56 PM, Heikki Linnakangas
> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>> On 04.01.2012 08:42, Amit Kapila wrote:
>>>
>>> Why PostgreSQL needs to write WAL record for Checkpoint when it maintains
>>> same information in pg_control file?
>>
>>
>> I guess it wouldn't be strictly necessary...
>
> Apart from replicated standbys, which need that info for running restartpoints.
Yeah.
But, the OP makes me wonder: why can a standby only perform a
restartpoint where the master performed a checkpoint? It seems like a
standby ought to be able to create a restartpoint anywhere, just by
writing everything, flushing it to disk, and update pg_control. I
assume there's some reason that doesn't work, I just don't know what
it is...
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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