Re: PG 13 release notes, first draft

On Tue, May 12, 2020 at 01:09:08PM +0900, Kyotaro Horiguchi wrote:
> > > commit c6b9204
> > > Author: Noah Misch <noah(at)leadboat(dot)com>
> > > AuthorDate: Sat Apr 4 12:25:34 2020 -0700
> > > Commit: Noah Misch <noah(at)leadboat(dot)com>
> > > CommitDate: Sat Apr 4 12:25:34 2020 -0700
> > >
> > > Skip WAL for new relfilenodes, under wal_level=minimal.
> > >
> > > Until now, only selected bulk operations (e.g. COPY) did this. If a
> > > given relfilenode received both a WAL-skipping COPY and a WAL-logged
> > > operation (e.g. INSERT), recovery could lose tuples from the COPY. See
> > > src/backend/access/transam/README section "Skipping WAL for New
> > > RelFileNode" for the new coding rules. Maintainers of table access
> > > methods should examine that section.
> >
> > OK, so how do we want to document this? Do I mention in the text below
> > the WAL skipping item that this fixes a bug where a mix of simultaneous
> > COPY and INSERT into a table could lose rows during crash recovery, or
> > create a new item?
>
> FWIW, as dicussed upthread, I suppose that the API change is not going
> to be in relnotes.
>
> something like this?
>
> - Fix bug of WAL-skipping optimiazation
>
> Previously a trasaction doing both of COPY and a WAL-logged operations
> like INSERT while wal_level=minimal can lead to loss of COPY'ed rows
> through crash recovery. Also this fix extends the WAL-skipping
> optimiazation to all kinds of bulk insert operations.

Uh, that kind of mixes the bug fix and the feature in a way that it is
hard to understand. How about this?

Allow skipping of WAL for new tables and indexes if wal_level is
'minimal' (Kyotaro Horiguchi)

Relations larger than wal_skip_threshold will have their files
fsync'ed rather than writing their WAL records. Previously this
was done only for COPY operations, but the implementation had a
bug that could cause data loss during crash recovery.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com

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