pg_receivexlog — stream transaction logs from a PostgreSQL™ server
pg_receivexlog
[option
...]
pg_receivexlog is used to stream 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 the section called “Continuous Archiving and Point-in-Time Recovery (PITR)”).
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.
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
the section called “Role Attributes”), 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 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.
-D directory
, --directory=directory
Directory to write the output to.
This parameter is required.
-n
, --no-loop
Don't loop on connection errors. Instead, exit right away with an error.
-s interval
, --status-interval=interval
Specifies the number of seconds between status packets sent back to the server. This allows for easier monitoring of the progress from server. A value of zero disables the periodic status updates completely, although an update will still be sent when requested by the server, to avoid timeout disconnect. The default value is 10 seconds.
-S slotname
, --slot=slotname
Require pg_receivexlog to use an existing replication slot (see the section called “Replication Slots”). When this option is used, pg_receivexlog will report a flush position to the server, indicating when each segment has been synchronized to disk so that the server can remove that segment if it is not otherwise needed. When using this parameter, it is important to make sure that pg_receivexlog cannot become the synchronous standby through an incautious setting of synchronous_standby_names; it does not flush data frequently enough for this to work correctly.
-v
, --verbose
Enables verbose mode.
The following command-line options control the database connection parameters.
-d connstr
, --dbname=connstr
Specifies parameters used to connect to the server, as a connection string. See the section called “Connection Strings” for more information.
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
Specifies the host name of the machine on which the server is
running. If the value begins with a slash, it is used as the
directory for the Unix domain socket. The default is taken
from the PGHOST
environment variable, if set,
else a Unix domain socket connection is attempted.
-p port
, --port=port
Specifies the TCP port or local Unix domain socket file
extension on which the server is listening for connections.
Defaults to the PGPORT
environment variable, if
set, or a compiled-in default.
-U username
, --username=username
User name to connect as.
-w
, --no-password
Never issue a password prompt. If the server requires
password authentication and a password is not available by
other means such as a .pgpass
file, the
connection attempt will fail. This option can be useful in
batch jobs and scripts where no user is present to enter a
password.
-W
, --password
Force pg_receivexlog to prompt for a password before connecting to a database.
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.
Other options are also available:
-V
, --version
Print the pg_receivexlog version and exit.
-?
, --help
Show help about pg_receivexlog command line arguments, and exit.
This utility, like most other PostgreSQL™ utilities, uses the environment variables supported by libpq (see the section called “Environment Variables”).
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.