PostgreSQL 10.0 preview 变化 - pg_xlog,pg_clog,pg_log目录更名为pg_wal,pg_xact,log
背景
10.0 把几个有一定“歧义”的目录更名了。它们分别为
pg_xlog, pg_clog, pg_log
更名为
pg_wal, pg_xact, log
分别对应WAL（write ahead log）日志，事务状态日志，日志。
省得有人误删其中的LOG目录中的文件。（还真有发生过）。
对应patch
Rename "pg_xlog" directory to "pg_wal".
author Robert Haas <rhaas@postgresql.org>
Thu, 20 Oct 2016 23:24:37 +0800 (11:24 -0400)
committer Robert Haas <rhaas@postgresql.org>
Thu, 20 Oct 2016 23:32:18 +0800 (11:32 -0400)
"xlog" is not a particularly clear abbreviation for "write-ahead log",
and it sometimes confuses users into believe that the contents of the
"pg_xlog" directory are not critical data, leading to unpleasant
consequences. So, rename the directory to "pg_wal".
This patch modifies pg_upgrade and pg_basebackup to understand both
the old and new directory layouts; the former is necessary given the
purpose of the tool, while the latter merely avoids an unnecessary
backward-compatibility break.
We may wish to consider renaming other programs, switches, and
functions which still use the old "xlog" naming to also refer to
"wal". However, that's still under discussion, so let's do just this
much for now.
Discussion: CAB7nPqTeC-8+zux8_-4ZD46V7YPwooeFxgndfsq5Rg8ibLVm1A@mail.gmail.com
Michael Paquier
Rename "pg_clog" directory to "pg_xact".
author Robert Haas <rhaas@postgresql.org>
Fri, 17 Mar 2017 21:46:58 +0800 (09:46 -0400)
committer Robert Haas <rhaas@postgresql.org>
Fri, 17 Mar 2017 21:48:38 +0800 (09:48 -0400)
Names containing the letters "log" sometimes confuse users into
believing that only non-critical data is present. It is hoped
this renaming will discourage ill-considered removals of transaction
status data.
Michael Paquier
Discussion: http://postgr.es/m/CA+Tgmoa9xFQyjRZupbdEFuwUerFTvC6HjZq1ud6GYragGDFFgA@mail.gmail.com
Change default of log_directory to 'log'
author Peter Eisentraut <peter_e@gmx.net>
Mon, 27 Mar 2017 22:34:33 +0800 (10:34 -0400)
committer Peter Eisentraut <peter_e@gmx.net>
Mon, 27 Mar 2017 22:34:33 +0800 (10:34 -0400)
The previous default 'pg_log' might have indicated by its "pg_" prefix
that it is an internal system directory. The new default is more in
line with the typical naming of directories with user-facing log files.
Together with the renaming of pg_clog and pg_xlog, this should clear up
that difference.
Author: Andreas Karlsson <andreas@proxel.se>
这个patch的讨论，详见邮件组，本文末尾URL。
PostgreSQL社区的作风非常严谨，一个patch可能在邮件组中讨论几个月甚至几年，根据大家的意见反复的修正，patch合并到master已经非常成熟，所以PostgreSQL的稳定性也是远近闻名的。
参考
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=f82ec32ac30ae7e3ec7c84067192535b2ff8ec0e
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=88e66d193fbaf756b3cc9bf94cad116aacbb355b
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=3371e4d9b12455fe1f8d1516d0bd915aab86be17