PostgreSQL中的升级，如果针对小版本的升级，比如9.6.1升级到9.6.2(当前的最新版本)，只需要用9.6.2版本的软件替换9.6.1版本的软件即可，不需要做额外的操作，因为整个大版本是相互兼容的，内部存储形式也是兼容的。但如果涉及到跨大版本升级比如9.4.11升级到9.6.2，这种直接替换软件就不行了，因为跨版本的内部存储形式发生了变化。
官方给了三种升级的方式来解决跨版本升级：
pg_dumpall
pg_upgrade
通过复制
pg_dumpall是一种把数据从旧版本逻辑导出，再导入新版本的方法，就是一个导出导入的过程。
通过复制的方式是创建一个高版本的从库，等数据同步完后主变备，备变主，达到升级的目的。
再一种是通过pg_upgrade命令的升级方式，它是一种快速升级的方法，通过创建新的系统表并使用旧的用户表的方式进行升级。它又分为两种方式：原地升级和非原地升级，原地升级需要指定--link参数。
下面介绍一下使用pg_upgrade做升级的大体步骤：
示例是从9.4.11升级到9.6.2。
1、安装新版本软件
新版本的软件需要保证与旧版本的软件在配置上兼容，pg_upgrade会在升级前检查pg_controldata，确保所有的设置是兼容的。
2、用新版本初始化一个新的数据库
[postgres@rhel7 ~]$ /opt/pgsql-9.6.2/bin/initdb -D /pgdata-new/
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.UTF-8".
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 /pgdata-new ... ok
creating subdirectories ... ok
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
selecting dynamic shared memory implementation ... posix
creating configuration files ... ok
running bootstrap script ... ok
performing post-bootstrap initialization ... 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:
/opt/pgsql-9.6.2/bin/pg_ctl -D /pgdata-new/ -l logfile start3、设置pg_hba.conf，保证pg_upgrade通过连接新旧两个库
4、停止旧库
#创建测试表
[postgres@rhel7 ~]$ psql
psql (9.4.11)
Type "help" for help.
^
postgres=# create table zx (id int);
CREATE TABLE
postgres=# \d
List of relations
Schema | Name | Type | Owner
--------+------+-------+----------
public | zx | table | postgres
(1 row)
postgres=# insert into zx values(1);
INSERT 0 1
postgres=# select * from zx;
id
----
1
(1 row)
#停止旧库
[postgres@rhel7 ~]$ /opt/pgsql-9.4/bin/pg_ctl stop -D /usr/local/pgsql/data/
waiting for server to shut down.... done
server stopped5、使用pg_upgrade执行升级
[postgres@rhel7 ~]$ /opt/pgsql-9.6.2/bin/pg_upgrade -d /usr/local/pgsql/data/ -D /pgdata-new/ -b /opt/pgsql-9.4/bin/ -B /opt/pgsql-9.6.2/bin/
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
Checking for roles starting with 'pg_' 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介绍下使用的参数-b指定旧版本软件的bin目录-B指定新版本软件的bin目录，-d指定旧版本对应的数据目录，-D指定新版本对应的数据目录。
6、启动新版本数据库并做检查
[postgres@rhel7 ~]$ /opt/pgsql-9.6.2/bin/pg_ctl start -D /pgdata-new/ -l logfile
server starting
[postgres@rhel7 ~]$ psql
psql (9.6.2)
Type "help" for help.
postgres=# \d
List of relations
Schema | Name | Type | Owner
--------+------+-------+----------
public | zx | table | postgres
(1 row)
postgres=# select * from zx;
id
----
1
(1 row)7、恢复配置文件如pg_hba.conf、postgresql.conf等
8、收集统计信息
由于升级过程中不会把统计信息传到新库系统表中，需要重新收集统计信息。pg_upgrade的最给出了收集统计信息的脚本：
[postgres@rhel7 ~]$ ./analyze_new_cluster.sh
This script will generate minimal optimizer statistics rapidly
so your system is usable, and then gather statistics twice more
with increasing accuracy. When it is done, your system will
have the default level of optimizer statistics.
If you have used ALTER TABLE to modify the statistics target for
any tables, you might want to remove them and restore them after
running this script because they will delay fast statistics generation.
If you would like default statistics as quickly as possible, cancel
this script and run:
"/opt/pgsql-9.6.2/bin/vacuumdb" --all --analyze-only
vacuumdb: processing database "postgres": Generating minimal optimizer statistics (1 target)
vacuumdb: processing database "template1": Generating minimal optimizer statistics (1 target)
vacuumdb: processing database "postgres": Generating medium optimizer statistics (10 targets)
vacuumdb: processing database "template1": Generating medium optimizer statistics (10 targets)
vacuumdb: processing database "postgres": Generating default (full) optimizer statistics
vacuumdb: processing database "template1": Generating default (full) optimizer statistics
Done9、升级成功后删除旧版本软件和数据。
官方文档：https://www.postgresql.org/docs/9.6/static/pgupgrade.html
https://www.postgresql.org/docs/9.6/static/upgrading.html
