Re: Renaming of pg_xlog and pg_clog

On 29 August 2016 at 14:30, Michael Paquier <michael(dot)paquier(at)gmail(dot)com> wrote:
> On Mon, Aug 29, 2016 at 2:36 PM, Craig Ringer
> <craig(dot)ringer(at)2ndquadrant(dot)com> wrote:
>> I don't care if it comes as part of some greater reorg or not but I'll be
>> really annoyed if scope creep lands up killing the original proposal to just
>> rename these dirs. I think that a simple rename should be done first. Then
>> if some greater reorg is to be done it can be done shortly after. The only
>> people that'll upset are folks tracking early 10.0 dev and they'll be aware
>> it's coming.
>
> Okay, so let's do it. Attached are two patches:
> - 0001 renames pg_clog to pg_trans. I have let clog.c with its current
> name, as well as its structures. That's the mechanical patch, the ony
> interesting part being in pg_upgrade.
> - 0002 renames pg_xlog to pg_wal.

Is there any expectation that a 10.0 pg_basebackup should work on a
9.x server, or fail to work gracefully? There doesn't look to be any
version specific handling of the rename there.

Otherwise looks good.

Doesn't upset 'make check' or the TAP recovery suite.

Works:

src/test/regress/tmp_check/data $ ls
base pg_commit_ts pg_hba.conf pg_logical pg_notify
pg_serial pg_stat pg_subtrans pg_trans PG_VERSION
postgresql.auto.conf postmaster.opts
global pg_dynshmem pg_ident.conf pg_multixact pg_replslot
pg_snapshots pg_stat_tmp pg_tblspc pg_twophase pg_wal
postgresql.conf

It leaves pg_xlogfilename etc with original names as it IMO should.
There's no need to break more than we have to and it's still the xlog.

The documentation on backup/restore might benefit from a note saying
that pg_wal was named pg_xlog prior to 10.0 so tools intended to work
on older versions should check PG_VERSION. Though in practice most
people who write new tools will target 10.0+ and people maintaining
older tools will know, so it's not a big deal.

I don't know if the renaming in XLogFileRead of XLOG_FROM_PG_XLOG =>
XLOG_FROM_PG_WAL is really necessary, but tend to think it's good
since that define explicitly refers to the directory name, not
transaction logs in general.

The patch does not update the translations. I wonder if it's worth
doing so to save translators the hassle by sed'ing the following
lines:

- errhint("The database server
will regularly poll the pg_xlog subdirectory to check for files placed
there.")));
+ errhint("The database server
will regularly poll the pg_wal subdirectory to check for files placed
there.")));

- (errmsg("could not open directory
\"%s\": %m", "pg_xlog")));
+ (errmsg("could not open directory
\"%s\": %m", "pg_wal")));

with

sed -i 's/\<pg_xlog\>/pg_wal/g' src/backend/po/*.po

?

src/backend/access/transam/README should probably have a note about the rename.

Looks like changes in pg_upgrade for clog are a bit more than the
mechanical changes elsewhere, but seem sensible to me. I haven't yet
done a test pg_upgrade run.

--
--
Craig Ringer http://www.2ndQuadrant.com/
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