pg_receivexlog Man page

PG_RECEIVEXLOG(1) PostgreSQL 9.5.5 Documentation PG_RECEIVEXLOG(1)

NAME

pg_receivexlog – stream transaction logs from a PostgreSQL server

SYNOPSIS

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 24.3, “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 20.2,
“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
Directory to write the output to.

This parameter is required.

–if-not-exists
Do not error out when –create-slot is specified and a slot with
the specified name already exists.

-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
Section 25.2.6, “Replication Slots”, in the documentation). 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 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
Flush the WAL data to disk immediately after it has been received.
Also send a status packet back to the server immediately after
flushing, regardless of –status-interval.

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
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 Section 31.1.1, “Connection Strings”, in the
documentation 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.

pg_receivexlog can perform one of the two following actions in order to
control physical replication slots:

–create-slot
Create a new physical replication slot with the name specified in
–slot, then exit.

–drop-slot
Drop the replication slot with the name specified in –slot, then
exit.

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.

ENVIRONMENT
This utility, like most other PostgreSQL utilities, uses the
environment variables supported by libpq (see Section 31.14,
“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

PostgreSQL 9.5.5 2016 PG_RECEIVEXLOG(1)