一、环境
CentOS7下8核的cpu，数据库的配置是initdb后默认的：
$ cat /etc/redhat-release
CentOS Linux release 7.0.1406 (Core)
$ uname -a
Linux zhaopin-2-203 3.10.0-123.el7.x86_64 #1 SMP Mon Jun 30 12:09:22 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$ cat /proc/cpuinfo | grep processor | wc -l
8
$ psql --version
psql (PostgreSQL) 9.4.5
$ psql -U postgres -d test
psql (9.4.5)
Type "help" for help.
test=# \dt+
List of relations
Schema | Name | Type | Owner | Size | Description
--------+-------+-------+----------+--------+-------------
public | test1 | table | postgres | 275 MB |
public | test2 | table | postgres | 275 MB |
public | test3 | table | postgres | 275 MB |
public | test4 | table | postgres | 275 MB |
public | test5 | table | postgres | 275 MB |
public | test6 | table | postgres | 275 MB |
public | test7 | table | postgres | 275 MB |
public | test8 | table | postgres | 275 MB |
(8 rows)
test=# \q二、参数
1. pg_dump
$ pg_dump --help
pg_dump dumps a database as a text file or to other formats.
Usage:
pg_dump [OPTION]... [DBNAME]
General options:
-f, --file=FILENAME output file or directory name
-F, --format=c|d|t|p output file format (custom, directory, tar,
plain text (default))
-j, --jobs=NUM use this many parallel jobs to dump
-v, --verbose verbose mode
-V, --version output version information, then exit
-Z, --compress=0-9 compression level for compressed formats
--lock-wait-timeout=TIMEOUT fail after waiting TIMEOUT for a table lock
-?, --help show this help, then exit
Options controlling the output content:
-a, --data-only dump only the data, not the schema
-b, --blobs include large objects in dump
-c, --clean clean (drop) database objects before recreating
-C, --create include commands to create database in dump
-E, --encoding=ENCODING dump the data in encoding ENCODING
-n, --schema=SCHEMA dump the named schema(s) only
-N, --exclude-schema=SCHEMA do NOT dump the named schema(s)
-o, --oids include OIDs in dump
-O, --no-owner skip restoration of object ownership in
plain-text format
-s, --schema-only dump only the schema, no data
-S, --superuser=NAME superuser user name to use in plain-text format
-t, --table=TABLE dump the named table(s) only
-T, --exclude-table=TABLE do NOT dump the named table(s)
-x, --no-privileges do not dump privileges (grant/revoke)
--binary-upgrade for use by upgrade utilities only
--column-inserts dump data as INSERT commands with column names
--disable-dollar-quoting disable dollar quoting, use SQL standard quoting
--disable-triggers disable triggers during data-only restore
--exclude-table-data=TABLE do NOT dump data for the named table(s)
--if-exists use IF EXISTS when dropping objects
--inserts dump data as INSERT commands, rather than COPY
--no-security-labels do not dump security label assignments
--no-synchronized-snapshots do not use synchronized snapshots in parallel jobs
--no-tablespaces do not dump tablespace assignments
--no-unlogged-table-data do not dump unlogged table data
--quote-all-identifiers quote all identifiers, even if not key words
--section=SECTION dump named section (pre-data, data, or post-data)
--serializable-deferrable wait until the dump can run without anomalies
--use-set-session-authorization
use SET SESSION AUTHORIZATION commands instead of
ALTER OWNER commands to set ownership
Connection options:
-d, --dbname=DBNAME database to dump
-h, --host=HOSTNAME database server host or socket directory
-p, --port=PORT database server port number
-U, --username=NAME connect as specified database user
-w, --no-password never prompt for password
-W, --password force password prompt (should happen automatically)
--role=ROLENAME do SET ROLE before dump
If no database name is supplied, then the PGDATABASE environment
variable value is used.
Report bugs to <pgsql-bugs@postgresql.org>.2. pg_restore
$ pg_restore --help
pg_restore restores a PostgreSQL database from an archive created by pg_dump.
Usage:
pg_restore [OPTION]... [FILE]
General options:
-d, --dbname=NAME connect to database name
-f, --file=FILENAME output file name
-F, --format=c|d|t backup file format (should be automatic)
-l, --list print summarized TOC of the archive
-v, --verbose verbose mode
-V, --version output version information, then exit
-?, --help show this help, then exit
Options controlling the restore:
-a, --data-only restore only the data, no schema
-c, --clean clean (drop) database objects before recreating
-C, --create create the target database
-e, --exit-on-error exit on error, default is to continue
-I, --index=NAME restore named index
-j, --jobs=NUM use this many parallel jobs to restore
-L, --use-list=FILENAME use table of contents from this file for
selecting/ordering output
-n, --schema=NAME restore only objects in this schema
-O, --no-owner skip restoration of object ownership
-P, --function=NAME(args) restore named function
-s, --schema-only restore only the schema, no data
-S, --superuser=NAME superuser user name to use for disabling triggers
-t, --table=NAME restore named table
-T, --trigger=NAME restore named trigger
-x, --no-privileges skip restoration of access privileges (grant/revoke)
-1, --single-transaction restore as a single transaction
--disable-triggers disable triggers during data-only restore
--if-exists use IF EXISTS when dropping objects
--no-data-for-failed-tables do not restore data of tables that could not be
created
--no-security-labels do not restore security labels
--no-tablespaces do not restore tablespace assignments
--section=SECTION restore named section (pre-data, data, or post-data)
--use-set-session-authorization
use SET SESSION AUTHORIZATION commands instead of
ALTER OWNER commands to set ownership
Connection options:
-h, --host=HOSTNAME database server host or socket directory
-p, --port=PORT database server port number
-U, --username=NAME connect as specified database user
-w, --no-password never prompt for password
-W, --password force password prompt (should happen automatically)
--role=ROLENAME do SET ROLE before restore
The options -I, -n, -P, -t, -T, and --section can be combined and specified
multiple times to select multiple objects.
If no input file name is supplied, then standard input is used.
Report bugs to <pgsql-bugs@postgresql.org>.可以看到pg_dump和pg_restore都有-j, --jobs=NUM参数，可以使用多线程并行。这个功能是从9.3开始支持的，具体相见release note：http://www.postgresql.org/docs/9.4/interactive/release-9-3.html
三、pg_dump备份数据对比
1. 单线程
$ rm -fr test; mkdir -p test; date '+%F %T'; pg_dump -U postgres -d test -F d -f test; date '+%F %T'
2015-11-05 17:10:04
2015-11-05 17:10:44
$ ps aux | grep pg_dump | grep -v grep
wenhang+ 50634 116 0.0 118424 2996 pts/1 R+ 17:10 0:02 pg_dump -U postgres -d test -F d -f test这条命令的意思是先删除test文件夹；再创建test文件夹；打印当前时间；使用pg_dump备份数据库到test目录，-F d是指定备份格式是目录；再打印当前时间。这两个时间差就是备份需要的时间1分40秒。
2. 多线程
$ rm -fr test; mkdir -p test; date '+%F %T'; pg_dump -U postgres -d test -j 8 -F d -f test; date '+%F %T'
2015-11-05 17:09:00
2015-11-05 17:09:14
$ ps aux | grep pg_dump | grep -v grep
wenhang+ 50546 0.0 0.0 118100 2668 pts/1 S+ 17:09 0:00 pg_dump -U postgres -d test -j 8 -F d -f test
wenhang+ 50548 85.9 0.0 120516 4136 pts/1 R+ 17:09 0:15 pg_dump -U postgres -d test -j 8 -F d -f test
wenhang+ 50549 84.8 0.0 120516 4200 pts/1 R+ 17:09 0:15 pg_dump -U postgres -d test -j 8 -F d -f test
wenhang+ 50550 86.3 0.0 120516 4264 pts/1 R+ 17:09 0:15 pg_dump -U postgres -d test -j 8 -F d -f test
wenhang+ 50551 84.8 0.0 120516 4324 pts/1 R+ 17:09 0:15 pg_dump -U postgres -d test -j 8 -F d -f test
wenhang+ 50552 87.3 0.0 120516 4344 pts/1 R+ 17:09 0:15 pg_dump -U postgres -d test -j 8 -F d -f test
wenhang+ 50553 86.8 0.0 121992 5820 pts/1 R+ 17:09 0:15 pg_dump -U postgres -d test -j 8 -F d -f test
wenhang+ 50554 86.5 0.0 120516 4392 pts/1 R+ 17:09 0:15 pg_dump -U postgres -d test -j 8 -F d -f test
wenhang+ 50556 85.7 0.0 120516 4208 pts/1 R+ 17:09 0:15 pg_dump -U postgres -d test -j 8 -F d -f test这里加了-j 8参数，使用8线程并行，只用了14秒，可见相差了很多倍。
使用目录格式备份的原因是并行备份只支持目录格式，否则会出现如下错误：
pg_dump: parallel backup only supported by the directory format四、pg_restore恢复数据对比
1. 单线程
$ psql -U postgres -c 'drop database if exists test;'; psql -U postgres -c 'create database test;'; date '+%F %T'; pg_restore -U postgres -d test -F d test ; date '+%F %T'
DROP DATABASE
CREATE DATABASE
2015-11-05 17:11:36
2015-11-05 17:13:20
$ ps aux | grep pg_restore | grep -v grep
wenhang+ 50758 26.0 0.0 116740 1200 pts/1 S+ 17:11 0:00 pg_restore -U postgres -d test -F d test这条命令的意思是先删除数据库test；再创建数据库test；打印当前时间；从test目录恢复数据库test；-F d是指定恢复格式是目录；再打印当前时间。这两个时间差就是恢复需要的时间差1分44秒。
2. 多线程
$ psql -U postgres -c 'drop database if exists test;'; psql -U postgres -c 'create database test;'; date '+%F %T'; pg_restore -U postgres -d test -j 8 -F d test ; date '+%F %T'
DROP DATABASE
CREATE DATABASE
2015-11-05 17:26:22
2015-11-05 17:26:56
$ ps aux | grep pg_restore | grep -v grep
wenhang+ 53848 0.0 0.0 116600 1264 pts/1 S+ 17:26 0:00 pg_restore -U postgres -d test -j 8 -F d test
wenhang+ 53850 11.7 0.0 116744 976 pts/1 S+ 17:26 0:02 pg_restore -U postgres -d test -j 8 -F d test
wenhang+ 53851 11.9 0.0 116744 976 pts/1 S+ 17:26 0:02 pg_restore -U postgres -d test -j 8 -F d test
wenhang+ 53852 12.1 0.0 116744 976 pts/1 S+ 17:26 0:02 pg_restore -U postgres -d test -j 8 -F d test
wenhang+ 53853 12.2 0.0 116744 976 pts/1 S+ 17:26 0:02 pg_restore -U postgres -d test -j 8 -F d test
wenhang+ 53854 12.0 0.0 116744 976 pts/1 S+ 17:26 0:02 pg_restore -U postgres -d test -j 8 -F d test
wenhang+ 53855 12.6 0.0 116744 976 pts/1 S+ 17:26 0:02 pg_restore -U postgres -d test -j 8 -F d test
wenhang+ 53857 11.6 0.0 116744 976 pts/1 S+ 17:26 0:02 pg_restore -U postgres -d test -j 8 -F d test
wenhang+ 53858 12.2 0.0 116744 976 pts/1 S+ 17:26 0:02 pg_restore -U postgres -d test -j 8 -F d test可见多线程恢复也快了不少，如果io更快的话，这个提升会更明显
来源：oschina
链接：https://my.oschina.net/u/2426299/blog/526611