# PostgreSQL参数学习：max_wal_senders

[作者 高健@博客园  luckyjackgao@gmail.com]

http://space.itpub.net/133735/viewspace-742081

http://www.postgresql.org/docs/9.3/static/app-pgbasebackup.html

The backup is made over a regular PostgreSQL connection, and uses the replication protocol. The connection must be made with a superuser or a user having REPLICATION permissions (see Section 20.2), and pg_hba.conf must explicitly permit the replication connection. The server must also be configured with max_wal_senders set high enough to leave at least one session available for the backup.

http://www.postgresql.org/docs/9.3/static/runtime-config-replication.html#GUC-MAX-WAL-SENDERS

max_wal_senders (integer)
Specifies the maximum number of concurrent connections from standby servers or streaming base backup clients (i.e., the maximum number of simultaneously running WAL sender processes). The default is zero, meaning replication is disabled. WAL sender processes count towards the total number of connections, so the parameter cannot be set higher than max_connections. This parameter can only be set at server start. wal_level must be set to archive or hot_standby to allow connections from standby servers.

pg_basebackup also counts against the total of receivers:
http://www.postgresql.org/docs/9.3/interactive/app-pgbasebackup.html

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