table of contents
- stretch 9.6.12-0+deb9u1
PG_RECEIVEXLOG(1) | PostgreSQL 9.6.12 Documentation | PG_RECEIVEXLOG(1) |
NAME¶
pg_receivexlog - stream transaction logs from a PostgreSQL serverSYNOPSIS¶
pg_receivexlog [option...]
DESCRIPTION¶
pg_receivexlog is used to stream the transaction log from a running PostgreSQL cluster. The transaction log is streamed using the streaming replication protocol, and is written to a local directory of files. This directory can be used as the archive location for doing a restore using point-in-time recovery (see Section 25.3, “Continuous Archiving and Point-in-Time Recovery (PITR)”, in the documentation).pg_receivexlog streams the transaction log in real time as it's being generated on the server, and does not wait for segments to complete like archive_command does. For this reason, it is not necessary to set archive_timeout when using pg_receivexlog.
Unlike the WAL receiver of a PostgreSQL standby server, pg_receivexlog by default flushes WAL data only when a WAL file is closed. The option --synchronous must be specified to flush WAL data in real time.
The transaction log is streamed 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 21.2, “Role Attributes”, in the documentation), and pg_hba.conf must 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 stream.
If the connection is lost, or if it cannot be initially established, with a non-fatal error, pg_receivexlog will retry the connection indefinitely, and reestablish streaming as soon as possible. To avoid this behavior, use the -n parameter.
OPTIONS¶
-D directory--directory=directory
This parameter is required.
--if-not-exists
-n
--no-loop
-s interval
--status-interval=interval
-S slotname
--slot=slotname
When the replication client of pg_receivexlog is configured on the server as a synchronous standby, then using a replication slot will report the flush position to the server, but only when a WAL file is closed. Therefore, that configuration will cause transactions on the primary to wait for a long time and effectively not work satisfactorily. The option --synchronous (see below) must be specified in addition to make this work correctly.
--synchronous
This option should be specified if the replication client of pg_receivexlog is configured on the server as a synchronous standby, to ensure that timely feedback is sent to the server.
-v
--verbose
The following command-line options control the database connection parameters.
-d connstr
--dbname=connstr
The option is called --dbname for consistency with other client applications, but because pg_receivexlog doesn't connect to any particular database in the cluster, database name in the connection string will be ignored.
-h host
--host=host
-p port
--port=port
-U username
--username=username
-w
--no-password
-W
--password
This option is never essential, since pg_receivexlog will automatically prompt for a password if the server demands password authentication. However, pg_receivexlog will waste a connection attempt finding out that the server wants a password. In some cases it is worth typing -W to avoid the extra connection attempt.
pg_receivexlog can perform one of the two following actions in order to control physical replication slots:
--create-slot
--drop-slot
Other options are also available:
-V
--version
-?
--help
ENVIRONMENT¶
This utility, like most other PostgreSQL utilities, uses the environment variables supported by libpq (see Section 32.14, “Environment Variables”, in the documentation).NOTES¶
When using pg_receivexlog instead of archive_command as the main WAL backup method, it is strongly recommended to use replication slots. Otherwise, the server is free to recycle or remove transaction log files before they are backed up, because it does not have any information, either from archive_command or the replication slots, about how far the WAL stream has been archived. Note, however, that a replication slot will fill up the server's disk space if the receiver does not keep up with fetching the WAL data.EXAMPLES¶
To stream the transaction log from the server at mydbserver and store it in the local directory /usr/local/pgsql/archive:$ pg_receivexlog -h mydbserver -D /usr/local/pgsql/archive
SEE ALSO¶
pg_basebackup(1)2019 | PostgreSQL 9.6.12 |