diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml index 5d7057daa1..e7d25184eb 100644 --- a/doc/src/sgml/high-availability.sgml +++ b/doc/src/sgml/high-availability.sgml @@ -1,4 +1,4 @@ - + High Availability, Load Balancing, and Replication @@ -523,8 +523,8 @@ protocol to make nodes agree on a serializable transactional order. archive_timeout parameter, which can be set as low as a few seconds. However such a low setting will substantially increase the bandwidth required for file shipping. - If you need a window of less than a minute or so, it is probably better - to consider record-based log shipping. + If you need a window of less than a minute or so, consider using + . @@ -762,19 +762,25 @@ if (!triggered) - PostgreSQL includes a simple streaming replication - mechanism, which allows the standby server to stay more up-to-date than - file-based log shipping. The standby connects to the primary - and the primary starts streaming WAL records from where the standby - left off, and continues streaming them as they are generated, without - waiting for the WAL file to be filled. So with streaming replication, - archive_timeout does not need to be changed to reduce - possible data loss. + Streaming replication allows a standby server to stay more up-to-date + than is possible with file-based log shipping. The standby connects + to the primary, which streams WAL records to the standby as they're + generated, without waiting for the WAL file to be filled. + + + + Streaming replication is asynchronous, so there is stilll a small delay + between committing a transaction in the primary and for the changes to + become visible in the standby. The delay is however much smaller than with + file-based log shipping, typically under one second assuming the standby + is powerful enough to keep up with the load. With streaming replication, + archive_timeout is not required to reduce the data loss + window. Streaming replication relies on file-based continuous archiving for - making the base backup and for allowing a standby to catch up if it is + making the base backup and for allowing the standby to catch up if it is disconnected from the primary for long enough for the primary to delete old WAL files still required by the standby. @@ -796,11 +802,10 @@ if (!triggered) Set up continuous archiving from the primary to a WAL archive located - in a directory on the standby server. Ensure that - , - and - - are set appropriately on the primary + in a directory on the standby server. In particular, set + and + + to archive WAL files in a location accessible from the standby (see ). @@ -808,7 +813,7 @@ if (!triggered) Set and authentication options - (see pg_hba.conf) so the standby server can connect to + (see pg_hba.conf) on the primary so that the standby server can connect to the replication pseudo-database on the primary server (see ).