Thread: Re: Hot standbys now support exporting snapshots while creating a logical replication slot
Re: Hot standbys now support exporting snapshots while creating a logical replication slot
From
Kevin K Biju
Date:
Hi Fuiji,
I wasn't aware that support for exporting snapshots goes as far back as v10. The change looks good.
Thanks,
Kevin
On Fri, May 23, 2025 at 7:12 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
On 2025/05/22 20:53, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/17/logicaldecoding-explanation.html
> Description:
>
> Hi,
> I'm referring to this bit at the very end of the page: Creation of a
> snapshot is not always possible. In particular, it will fail when connected
> to a hot standby. Applications that do not require snapshot export may
> suppress it with the NOEXPORT_SNAPSHOT option.
> It's not clear what the intention of this is (is it referring only to
> physical replication slots?) but as it stands you can export snapshots while
> creating a logical replication slot. This should have been possible starting
> PG16, I've tested this on PG17.
The description "Creation of a snapshot is not always possible. In particular,
it will fail when connected to a hot standby." no longer seems accurate.
Since v10 (commit 6c2003f8a1b), exporting snapshots on a standby has been supported.
This description was accurate when the first patch [1] adding that description
was written, but I think we just overlooked updating it later.
> As an aside, I think NOEXPORT_SNAPSHOT is from the older syntax of
> CREATE_REPLICATION_SLOT and should be swapped with SNAPSHOT 'nothing'.
Yes, so how about the following change?
<para>
- Creation of a snapshot is not always possible. In particular, it will
- fail when connected to a hot standby. Applications that do not require
- snapshot export may suppress it with the <literal>NOEXPORT_SNAPSHOT</literal>
+ Applications that do not require
+ snapshot export may suppress it with the <literal>SNAPSHOT 'nothing'</literal>
option.
</para>
Regards,
[1] https://www.postgresql.org/message-id/CAMsr+YFjxv0T8Yi1Q=3tVdgViU2bm+fb_-XUbTfxHsnLDNSkzg@mail.gmail.com
Regards,
--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
Re: Hot standbys now support exporting snapshots while creating a logical replication slot
From
Fujii Masao
Date:
On 2025/05/23 23:46, Fujii Masao wrote: > > > On 2025/05/23 19:52, Kevin K Biju wrote: >> Hi Fuiji, >> >> I wasn't aware that support for exporting snapshots goes as far back as v10. The change looks good. > > Thanks for the review! > > I've prepared two patches: one for v15 and later, and another for v13 and v14. > Unless there are any objections, I'll go ahead and commit and back-patch the patch > to all supported branches. I've pushed the patch. Thanks! Regards, -- Fujii Masao NTT DATA Japan Corporation