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 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 21.2) 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
       (Control+C) or SIGTERM signal.

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
       -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.

           This option is called --dbname for consistency with other client applications, but
           because pg_receivewal doesn't connect to any particular database in the cluster, any
           database name included in the connection string will be ignored by the server.
           However, a database name supplied that way overrides the default database name
           (replication) for purposes of looking up the replication connection's password in
           ~/.pgpass. Similarly, middleware or proxies used in connecting to PostgreSQL might
           utilize the name for purposes such as connection routing.

       -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 or SIGTERM 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 32.15).

       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)