Re: wal_init_zero and wal_recycle

On Wed, May 27, 2020 at 7:09 PM Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On Wed, 27 May 2020 at 04:27, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote:
>>
>> Hi,
>>
>> The group of wal_init_zero and wal_recycle is WAL_SETTINGS in guc.c,
>> but their descriptions are located in "19.6. Replication"/"19.6.1. Sending
>> Servers" section. This seems a documentation bug. They should be located
>> in "19.5. Write Ahead Log"/"19.5.1. Settings". Thought?
>
>
> +1
>
> Why are there two settings for the same thing (COW support)?
> Would we really want to allow setting one but not the other?

In the long discussion[1] we decided to invent GUCs that tell you
precisely what they do, rather than trying to have a mysterious "COW
filesystem mode", given the apparent lack of COW filesystem expertise
in the thread (for example: claims, theories and data about ZFS were
presented, but do they also apply to BTRFS, APFS, ReFS, ...? I dunno,
and no one showed up with more information on that.)

[1] https://www.postgresql.org/message-id/flat/CACPQ5Fo00QR7LNAcd1ZjgoBi4y97%2BK760YABs0vQHH5dLdkkMA%40mail.gmail.com