PG_RECEIVEWAL(1) PostgreSQL 15.7 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 26.3).
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 and archive_library do. 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
user having REPLICATION permissions (see Section 22.2) or a superuser,
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.
The starting point of the write-ahead log streaming is calculated when
pg_receivewal starts:
1. First, scan the directory where the WAL segment files are written
and find the newest completed segment file, using as the starting
point the beginning of the next WAL segment file.
2. If a starting point cannot be calculated with the previous method,
and if a replication slot is used, an extra READ_REPLICATION_SLOT
command is issued to retrieve the slot's restart_lsn to use as the
starting point. This option is only available when streaming
write-ahead logs from PostgreSQL 15 and up.
3. If a starting point cannot be calculated with the previous method,
the latest WAL flush location is used as reported by the server
from an IDENTIFY_SYSTEM command.
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 27.2.6). 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
-Z method[:detail]
--compress=level
--compress=method[:detail]
Enables compression of write-ahead logs.
The compression method can be set to gzip, lz4 (if PostgreSQL was
compiled with --with-lz4) or none for no compression. A compression
detail string can optionally be specified. If the detail string is
an integer, it specifies the compression level. Otherwise, it
should be a comma-separated list of items, each of the form keyword
or keyword=value. Currently, the only supported keyword is level.
If no compression level is specified, the default compression level
will be used. If only a level is specified without mentioning an
algorithm, gzip compression will be used if the level is greater
than 0, and no compression will be used if the level is 0.
The suffix .gz will automatically be added to all filenames when
using gzip, and the suffix .lz4 is added when using lz4.
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; these will override any conflicting command line options.
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 34.15).
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 or archive_library
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 archive_library 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 15.7 2024 PG_RECEIVEWAL(1)
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