| pg_receivewal(1) - phpMan
PG_RECEIVEWAL(1) PostgreSQL 12.3 Documentation PG_RECEIVEWAL(1)
NAME
pg_receivewal - stream write-ahead logs from a PostgreSQL server
SYNOPSIS
pg_receivewal [option...]
DESCRIPTION
pg_receivewal is used to stream the write-ahead log from a running PostgreSQL cluster. The
write-ahead 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).
pg_receivewal streams the write-ahead 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_receivewal.
Unlike the WAL receiver of a PostgreSQL standby server, pg_receivewal 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. Since pg_receivewal does not apply WAL, you should not allow
it to become a synchronous standby when synchronous_commit equals remote_apply. If it
does, it will appear to be a standby that never catches up, and will cause transaction
commits to block. To avoid this, you should either configure an appropriate value for
synchronous_standby_names, or specify application_name for pg_receivewal that does not
match it, or change the value of synchronous_commit to something other than remote_apply.
The write-ahead 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), 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_receivewal will retry the connection indefinitely, and reestablish streaming as
soon as possible. To avoid this behavior, use the -n parameter.
In the absence of fatal errors, pg_receivewal will run until terminated by the SIGINT
signal (Control+C).
OPTIONS
-D directory
--directory=directory
Directory to write the output to.
This parameter is required.
-E lsn
--endpos=lsn
Automatically stop replication and exit with normal exit status 0 when receiving
reaches the specified LSN.
If there is a record with LSN exactly equal to lsn, the record will be processed.
--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.
--no-sync
This option causes pg_receivewal to not force WAL data to be flushed to disk. This is
faster, but means that a subsequent operating system crash can leave the WAL segments
corrupt. Generally, this option is useful for testing but should not be used when
doing WAL archiving on a production deployment.
This option is incompatible with --synchronous.
-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_receivewal to use an existing replication slot (see Section 26.2.6). When
this option is used, pg_receivewal 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_receivewal 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_receivewal is
configured on the server as a synchronous standby, to ensure that timely feedback is
sent to the server.
-v
--verbose
Enables verbose mode.
-Z level
--compress=level
Enables gzip compression of write-ahead logs, and specifies the compression level (0
through 9, 0 being no compression and 9 being best compression). The suffix .gz will
automatically be added to all filenames.
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 33.1.1 for more information.
The option is called --dbname for consistency with other client applications, but
because pg_receivewal 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_receivewal to prompt for a password before connecting to a database.
This option is never essential, since pg_receivewal will automatically prompt for a
password if the server demands password authentication. However, pg_receivewal 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_receivewal 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_receivewal version and exit.
-?
--help
Show help about pg_receivewal command line arguments, and exit.
EXIT STATUS
pg_receivewal will exit with status 0 when terminated by the SIGINT signal. (That is the
normal way to end it. Hence it is not an error.) For fatal errors or other signals, the
exit status will be nonzero.
ENVIRONMENT
This utility, like most other PostgreSQL utilities, uses the environment variables
supported by libpq (see Section 33.14).
The environment variable PG_COLOR specifies whether to use color in diagnostic messages.
Possible values are always, auto and never.
NOTES
When using pg_receivewal 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 write-ahead 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.
pg_receivewal will preserve group permissions on the received WAL files if group
permissions are enabled on the source cluster.
EXAMPLES
To stream the write-ahead log from the server at mydbserver and store it in the local
directory /usr/local/pgsql/archive:
$ pg_receivewal -h mydbserver -D /usr/local/pgsql/archive
SEE ALSO
pg_basebackup(1)
PostgreSQL 12.3 2020 PG_RECEIVEWAL(1)
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