用 Docker 把 PostgreSQL 数据库从 9.4 升级到 9.5

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杯具是如何开始的

由于使用 Atlassian 产品的缘故，一直在服务器上跑着一个 PostgreSQL。之前在配置服务的时候，直接用的是 latest 标签的镜像，然后手贱运行了 docker pull postgres 升级了 Docker 镜像。然后……然后……服务器就挂了，跑不起来了（懵逼脸）。看了一下，原来最新的官方 PostgreSQL 已经是 9.5 了，而我当时 pull 下来的 latest 实际上是 9.4。这个事情教育我们，生产环境的镜像最好使用版本号 tag 而不要偷懒使用 latest。

既然杯具已经发生了，那么该解决的问题还是要解决的。看了一下，PostgreSQL 官方的升级建议是使用 pg_upgrade 来处理新旧数据库，但是有个棘手的问题，就是必须同时有 9.4 和 9.5 两个版本的 PostgreSQL，否则无法升级数据库。

准备工作

因为我是使用 -v 来映射目录的，所以不用 --volumes-from 的方式来加载 Volume。因此，简单处理一下目录，把所有的 containers 都先 stop 掉，然后把待升级的数据库目录改个名，同时新建一个同名目录用于保存升级后的数据。

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mv postgres postgres_old
mkdir postgres
chown 999.999 postgres
chmod 700 postgres

其中用户 999.999 对应的是 container 里面的用户 postgres:postgres。

接下来就是用新版本的 PostgreSQL 来初始化数据库，以便后续数据库升级：

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$ docker run --name="postgres_new" -v /path/to/postgres:/var/lib/postgresql/data -ti --rm postgres:9.5
The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.utf8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

fixing permissions on existing directory /var/lib/postgresql/data ... ok
creating subdirectories ... ok
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
selecting dynamic shared memory implementation ... posix
creating configuration files ... ok
creating template1 database in /var/lib/postgresql/data/base/1 ... ok
initializing pg_authid ... ok
initializing dependencies ... ok
creating system views ... ok
loading system objects' descriptions ... ok
creating collations ... ok
creating conversions ... ok
creating dictionaries ... ok
setting privileges on built-in objects ... ok
creating information schema ... ok
loading PL/pgSQL server-side language ... ok
vacuuming database template1 ... ok
copying template1 to template0 ... ok
copying template1 to postgres ... ok
syncing data to disk ... ok

WARNING: enabling "trust" authentication for local connections
You can change this by editing pg_hba.conf or using the option -A, or
--auth-local and --auth-host, the next time you run initdb.

Success. You can now start the database server using:

    pg_ctl -D /var/lib/postgresql/data -l logfile start

****************************************************
WARNING: No password has been set for the database.
         This will allow anyone with access to the
         Postgres port to access your database. In
         Docker's default configuration, this is
         effectively any other container on the same
         system.

         Use "-e POSTGRES_PASSWORD=password" to set
         it in "docker run".
****************************************************
waiting for server to start....LOG:  database system was shut down at 2016-08-14 15:49:36 UTC
LOG:  MultiXact member wraparound protections are now enabled
LOG:  database system is ready to accept connections
LOG:  autovacuum launcher started
 done
server started
ALTER ROLE


/docker-entrypoint.sh: ignoring /docker-entrypoint-initdb.d/*

LOG:  received fast shutdown request
LOG:  aborting any active transactions
waiting for server to shut down...LOG:  autovacuum launcher shutting down
.LOG:  shutting down
LOG:  database system is shut down
 done
server stopped

PostgreSQL init process complete; ready for start up.

LOG:  database system was shut down at 2016-08-14 15:49:40 UTC
LOG:  MultiXact member wraparound protections are now enabled
LOG:  database system is ready to accept connections
LOG:  autovacuum launcher started
^C
LOG:  received fast shutdown request
LOG:  aborting any active transactions
LOG:  autovacuum launcher shutting down
LOG:  shutting down
LOG:  database system is shut down

这样，我们就得到了一个新的 9.5 版本的初始化数据库。

升级数据库

首先从待升级的 container 获得 9.4 版本 PostgreSQL 的运行文件和共享文件：

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docker cp postgres_old:/usr/lib/postgresql/9.4 .
docker cp postgres_old:/usr/share/postgresql/9.4 9.4s

然后创建一个临时的 container 来升级数据库

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$ docker run --name="tmp" -v $(pwd)/9.4:/usr/lib/postgresql/9.4 -v $(pwd)/9.4s:/usr/share/postgresql/9.4 -v /path/to/postgres:/data/new -v /path/to/postgres_old:/data/old -ti --rm postgres:9.5 bash
  • /path/to/postgres 是新数据库的路径
  • /path/to/postgres_old 是 9.4 版本的旧数据库的路径

在 container 中运行 su - postgres 把用户切换成 postgres，然后运行如下命令来升级数据库：

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$ cd /tmp
$ /usr/lib/postgresql/9.5/bin/pg_upgrade -b /usr/lib/postgresql/9.4/bin -B /usr/lib/postgresql/9.5/bin -d /data/old -D /data/new
Performing Consistency Checks
-----------------------------
Checking cluster versions                                   ok
Checking database user is the install user                  ok
Checking database connection settings                       ok
Checking for prepared transactions                          ok
Checking for reg* system OID user data types                ok
Checking for contrib/isn with bigint-passing mismatch       ok
Creating dump of global objects                             ok
Creating dump of database schemas
                                                            ok
Checking for presence of required libraries                 ok
Checking database user is the install user                  ok
Checking for prepared transactions                          ok

If pg_upgrade fails after this point, you must re-initdb the
new cluster before continuing.

Performing Upgrade
------------------
Analyzing all rows in the new cluster                       ok
Freezing all rows on the new cluster                        ok
Deleting files from new pg_clog                             ok
Copying old pg_clog to new server                           ok
Setting next transaction ID and epoch for new cluster       ok
Deleting files from new pg_multixact/offsets                ok
Copying old pg_multixact/offsets to new server              ok
Deleting files from new pg_multixact/members                ok
Copying old pg_multixact/members to new server              ok
Setting next multixact ID and offset for new cluster        ok
Resetting WAL archives                                      ok
Setting frozenxid and minmxid counters in new cluster       ok
Restoring global objects in the new cluster                 ok
Restoring database schemas in the new cluster
                                                            ok
Copying user relation files
                                                            ok
Setting next OID for new cluster                            ok
Sync data directory to disk                                 ok
Creating script to analyze new cluster                      ok
Creating script to delete old cluster                       ok

Upgrade Complete
----------------
Optimizer statistics are not transferred by pg_upgrade so,
once you start the new server, consider running:
    ./analyze_new_cluster.sh

Running this script will delete the old cluster's data files:
    ./delete_old_cluster.sh

好了，经过上述几步，数据库就升级完毕了，接下来重启各种服务，完美！