postgresql/doc/src/sgml/ref/pg_receivewal.sgml

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<!--
doc/src/sgml/ref/pg_receivewal.sgml
PostgreSQL documentation
-->
<refentry id="app-pgreceivewal">
<indexterm zone="app-pgreceivewal">
<primary>pg_receivewal</primary>
</indexterm>
<refmeta>
<refentrytitle><application>pg_receivewal</application></refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo>Application</refmiscinfo>
</refmeta>
<refnamediv>
<refname>pg_receivewal</refname>
<refpurpose>stream write-ahead logs from a <productname>PostgreSQL</productname> server</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>pg_receivewal</command>
<arg rep="repeat"><replaceable>option</replaceable></arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<application>pg_receivewal</application> is used to stream the write-ahead log
from a running <productname>PostgreSQL</productname> 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
<xref linkend="continuous-archiving"/>).
</para>
<para>
<application>pg_receivewal</application> 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 <xref linkend="guc-archive-command"/> and
<xref linkend="guc-archive-library"/> do.
For this reason, it is not necessary to set
<xref linkend="guc-archive-timeout"/> when using
<application>pg_receivewal</application>.
</para>
<para>
Unlike the WAL receiver of a PostgreSQL standby server, <application>pg_receivewal</application>
by default flushes WAL data only when a WAL file is closed.
The option <option>--synchronous</option> must be specified to flush WAL data
in real time. Since <application>pg_receivewal</application> does not
apply WAL, you should not allow it to become a synchronous standby when
<xref linkend="guc-synchronous-commit"/> equals
<literal>remote_apply</literal>. 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 <xref linkend="guc-synchronous-standby-names"/>, or specify
<varname>application_name</varname> for
<application>pg_receivewal</application> that does not match it, or
change the value of <varname>synchronous_commit</varname> to
something other than <literal>remote_apply</literal>.
</para>
<para>
The write-ahead log is streamed over a regular
<productname>PostgreSQL</productname> connection and uses the replication
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protocol. The connection must be made with a user having
<literal>REPLICATION</literal> permissions (see
<xref linkend="role-attributes"/>) or a superuser, and
<filename>pg_hba.conf</filename> must permit the replication connection.
The server must also be configured with
<xref linkend="guc-max-wal-senders"/> set high enough to leave at least
one session available for the stream.
</para>
<para>
The starting point of the write-ahead log streaming is calculated when
<application>pg_receivewal</application> starts:
<orderedlist>
<listitem>
<para>
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.
</para>
</listitem>
<listitem>
<para>
If a starting point cannot be calculated with the previous method,
and if a replication slot is used, an extra
<command>READ_REPLICATION_SLOT</command> command is issued to retrieve
the slot's <literal>restart_lsn</literal> to use as the starting point.
This option is only available when streaming write-ahead logs from
<productname>PostgreSQL</productname> 15 and up.
</para>
</listitem>
<listitem>
<para>
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 <literal>IDENTIFY_SYSTEM</literal> command.
</para>
</listitem>
</orderedlist>
</para>
<para>
If the connection is lost, or if it cannot be initially established,
with a non-fatal error, <application>pg_receivewal</application> will
retry the connection indefinitely, and reestablish streaming as soon
as possible. To avoid this behavior, use the <literal>-n</literal>
parameter.
</para>
<para>
In the absence of fatal errors, <application>pg_receivewal</application>
will run until terminated by the <systemitem>SIGINT</systemitem>
(<keycombo action="simul"><keycap>Control</keycap><keycap>C</keycap></keycombo>)
or <systemitem>SIGTERM</systemitem> signal.
</para>
</refsect1>
<refsect1>
<title>Options</title>
<variablelist>
<varlistentry>
<term><option>-D <replaceable class="parameter">directory</replaceable></option></term>
<term><option>--directory=<replaceable class="parameter">directory</replaceable></option></term>
<listitem>
<para>
Directory to write the output to.
</para>
<para>
This parameter is required.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-E <replaceable>lsn</replaceable></option></term>
<term><option>--endpos=<replaceable>lsn</replaceable></option></term>
<listitem>
<para>
Automatically stop replication and exit with normal exit status 0 when
receiving reaches the specified LSN.
</para>
<para>
If there is a record with LSN exactly equal to <replaceable>lsn</replaceable>,
the record will be processed.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--if-not-exists</option></term>
<listitem>
<para>
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Do not error out when <option>--create-slot</option> is specified
and a slot with the specified name already exists.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-n</option></term>
<term><option>--no-loop</option></term>
<listitem>
<para>
Don't loop on connection errors. Instead, exit right away with
an error.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--no-sync</option></term>
<listitem>
<para>
This option causes <command>pg_receivewal</command> 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.
</para>
<para>
This option is incompatible with <literal>--synchronous</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-s <replaceable class="parameter">interval</replaceable></option></term>
<term><option>--status-interval=<replaceable class="parameter">interval</replaceable></option></term>
<listitem>
<para>
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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-S <replaceable>slotname</replaceable></option></term>
<term><option>--slot=<replaceable class="parameter">slotname</replaceable></option></term>
<listitem>
<para>
Require <application>pg_receivewal</application> to use an existing
replication slot (see <xref linkend="streaming-replication-slots"/>).
When this option is used, <application>pg_receivewal</application> 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.
</para>
<para>
When the replication client
of <application>pg_receivewal</application> 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 <literal>--synchronous</literal> (see
below) must be specified in addition to make this work correctly.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--synchronous</option></term>
<listitem>
<para>
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 <literal>--status-interval</literal>.
</para>
<para>
This option should be specified if the replication client
of <application>pg_receivewal</application> is configured on the
server as a synchronous standby, to ensure that timely feedback is
sent to the server.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-v</option></term>
<term><option>--verbose</option></term>
<listitem>
<para>
Enables verbose mode.
</para>
</listitem>
</varlistentry>
Rework compression options of pg_receivewal pg_receivewal includes since cada1af the option --compress, to allow the compression of WAL segments using gzip, with a value of 0 (the default) meaning that no compression can be used. This commit introduces a new option, called --compression-method, able to use as values "none", the default, and "gzip", to make things more extensible. The case of --compress=0 becomes fuzzy with this option layer, so we have made the choice to make pg_receivewal return an error when using "none" and a non-zero compression level, meaning that the authorized values of --compress are now [1,9] instead of [0,9]. Not specifying --compress with "gzip" as compression method makes pg_receivewal use the default of zlib instead (Z_DEFAULT_COMPRESSION). The code in charge of finding the streaming start LSN when scanning the existing archives is refactored and made more extensible. While on it, rename "compression" to "compression_level" in walmethods.c, to reduce the confusion with the introduction of the compression method, even if the tar method used by pg_basebackup does not rely on the compression method (yet, at least), but just on the compression level (this area could be improved more, actually). This is in preparation for an upcoming patch that adds LZ4 support to pg_receivewal. Author: Georgios Kokolatos Reviewed-by: Michael Paquier, Jian Guo, Magnus Hagander, Dilip Kumar, Robert Haas Discussion: https://postgr.es/m/ZCm1J5vfyQ2E6dYvXz8si39HQ2gwxSZ3IpYaVgYa3lUwY88SLapx9EEnOf5uEwrddhx2twG7zYKjVeuP5MwZXCNPybtsGouDsAD1o2L_I5E=@pm.me
2021-11-04 03:10:31 +01:00
<varlistentry>
<term><option>-Z <replaceable class="parameter">level</replaceable></option></term>
<term><option>-Z <replaceable class="parameter">method</replaceable>[:<replaceable>detail</replaceable>]</option></term>
<term><option>--compress=<replaceable class="parameter">level</replaceable></option></term>
<term><option>--compress=<replaceable class="parameter">method</replaceable>[:<replaceable>detail</replaceable>]</option></term>
Rework compression options of pg_receivewal pg_receivewal includes since cada1af the option --compress, to allow the compression of WAL segments using gzip, with a value of 0 (the default) meaning that no compression can be used. This commit introduces a new option, called --compression-method, able to use as values "none", the default, and "gzip", to make things more extensible. The case of --compress=0 becomes fuzzy with this option layer, so we have made the choice to make pg_receivewal return an error when using "none" and a non-zero compression level, meaning that the authorized values of --compress are now [1,9] instead of [0,9]. Not specifying --compress with "gzip" as compression method makes pg_receivewal use the default of zlib instead (Z_DEFAULT_COMPRESSION). The code in charge of finding the streaming start LSN when scanning the existing archives is refactored and made more extensible. While on it, rename "compression" to "compression_level" in walmethods.c, to reduce the confusion with the introduction of the compression method, even if the tar method used by pg_basebackup does not rely on the compression method (yet, at least), but just on the compression level (this area could be improved more, actually). This is in preparation for an upcoming patch that adds LZ4 support to pg_receivewal. Author: Georgios Kokolatos Reviewed-by: Michael Paquier, Jian Guo, Magnus Hagander, Dilip Kumar, Robert Haas Discussion: https://postgr.es/m/ZCm1J5vfyQ2E6dYvXz8si39HQ2gwxSZ3IpYaVgYa3lUwY88SLapx9EEnOf5uEwrddhx2twG7zYKjVeuP5MwZXCNPybtsGouDsAD1o2L_I5E=@pm.me
2021-11-04 03:10:31 +01:00
<listitem>
<para>
Enables compression of write-ahead logs.
Rework compression options of pg_receivewal pg_receivewal includes since cada1af the option --compress, to allow the compression of WAL segments using gzip, with a value of 0 (the default) meaning that no compression can be used. This commit introduces a new option, called --compression-method, able to use as values "none", the default, and "gzip", to make things more extensible. The case of --compress=0 becomes fuzzy with this option layer, so we have made the choice to make pg_receivewal return an error when using "none" and a non-zero compression level, meaning that the authorized values of --compress are now [1,9] instead of [0,9]. Not specifying --compress with "gzip" as compression method makes pg_receivewal use the default of zlib instead (Z_DEFAULT_COMPRESSION). The code in charge of finding the streaming start LSN when scanning the existing archives is refactored and made more extensible. While on it, rename "compression" to "compression_level" in walmethods.c, to reduce the confusion with the introduction of the compression method, even if the tar method used by pg_basebackup does not rely on the compression method (yet, at least), but just on the compression level (this area could be improved more, actually). This is in preparation for an upcoming patch that adds LZ4 support to pg_receivewal. Author: Georgios Kokolatos Reviewed-by: Michael Paquier, Jian Guo, Magnus Hagander, Dilip Kumar, Robert Haas Discussion: https://postgr.es/m/ZCm1J5vfyQ2E6dYvXz8si39HQ2gwxSZ3IpYaVgYa3lUwY88SLapx9EEnOf5uEwrddhx2twG7zYKjVeuP5MwZXCNPybtsGouDsAD1o2L_I5E=@pm.me
2021-11-04 03:10:31 +01:00
</para>
<para>
The compression method can be set to <literal>gzip</literal>,
<literal>lz4</literal> (if <productname>PostgreSQL</productname>
was compiled with <option>--with-lz4</option>) or
<literal>none</literal> 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 <literal>keyword</literal> or <literal>keyword=value</literal>.
Currently, the only supported keyword is <literal>level</literal>.
Rework compression options of pg_receivewal pg_receivewal includes since cada1af the option --compress, to allow the compression of WAL segments using gzip, with a value of 0 (the default) meaning that no compression can be used. This commit introduces a new option, called --compression-method, able to use as values "none", the default, and "gzip", to make things more extensible. The case of --compress=0 becomes fuzzy with this option layer, so we have made the choice to make pg_receivewal return an error when using "none" and a non-zero compression level, meaning that the authorized values of --compress are now [1,9] instead of [0,9]. Not specifying --compress with "gzip" as compression method makes pg_receivewal use the default of zlib instead (Z_DEFAULT_COMPRESSION). The code in charge of finding the streaming start LSN when scanning the existing archives is refactored and made more extensible. While on it, rename "compression" to "compression_level" in walmethods.c, to reduce the confusion with the introduction of the compression method, even if the tar method used by pg_basebackup does not rely on the compression method (yet, at least), but just on the compression level (this area could be improved more, actually). This is in preparation for an upcoming patch that adds LZ4 support to pg_receivewal. Author: Georgios Kokolatos Reviewed-by: Michael Paquier, Jian Guo, Magnus Hagander, Dilip Kumar, Robert Haas Discussion: https://postgr.es/m/ZCm1J5vfyQ2E6dYvXz8si39HQ2gwxSZ3IpYaVgYa3lUwY88SLapx9EEnOf5uEwrddhx2twG7zYKjVeuP5MwZXCNPybtsGouDsAD1o2L_I5E=@pm.me
2021-11-04 03:10:31 +01:00
</para>
<para>
If no compression level is specified, the default compression level
will be used. If only a level is specified without mentioning an
algorithm, <literal>gzip</literal> compression will be used if the
level is greater than 0, and no compression will be used if the level
is 0.
Rework compression options of pg_receivewal pg_receivewal includes since cada1af the option --compress, to allow the compression of WAL segments using gzip, with a value of 0 (the default) meaning that no compression can be used. This commit introduces a new option, called --compression-method, able to use as values "none", the default, and "gzip", to make things more extensible. The case of --compress=0 becomes fuzzy with this option layer, so we have made the choice to make pg_receivewal return an error when using "none" and a non-zero compression level, meaning that the authorized values of --compress are now [1,9] instead of [0,9]. Not specifying --compress with "gzip" as compression method makes pg_receivewal use the default of zlib instead (Z_DEFAULT_COMPRESSION). The code in charge of finding the streaming start LSN when scanning the existing archives is refactored and made more extensible. While on it, rename "compression" to "compression_level" in walmethods.c, to reduce the confusion with the introduction of the compression method, even if the tar method used by pg_basebackup does not rely on the compression method (yet, at least), but just on the compression level (this area could be improved more, actually). This is in preparation for an upcoming patch that adds LZ4 support to pg_receivewal. Author: Georgios Kokolatos Reviewed-by: Michael Paquier, Jian Guo, Magnus Hagander, Dilip Kumar, Robert Haas Discussion: https://postgr.es/m/ZCm1J5vfyQ2E6dYvXz8si39HQ2gwxSZ3IpYaVgYa3lUwY88SLapx9EEnOf5uEwrddhx2twG7zYKjVeuP5MwZXCNPybtsGouDsAD1o2L_I5E=@pm.me
2021-11-04 03:10:31 +01:00
</para>
<para>
The suffix <filename>.gz</filename> will automatically be added to
all filenames when using <literal>gzip</literal>, and the suffix
<filename>.lz4</filename> is added when using <literal>lz4</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
The following command-line options control the database connection parameters.
<variablelist>
<varlistentry>
<term><option>-d <replaceable class="parameter">connstr</replaceable></option></term>
<term><option>--dbname=<replaceable class="parameter">connstr</replaceable></option></term>
<listitem>
<para>
Specifies parameters used to connect to the server, as a <link
linkend="libpq-connstring">connection string</link>; these
will override any conflicting command line options.
</para>
<para>
The option is called <literal>--dbname</literal> for consistency with other
client applications, but because <application>pg_receivewal</application>
doesn't connect to any particular database in the cluster, database
name in the connection string will be ignored.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-h <replaceable class="parameter">host</replaceable></option></term>
<term><option>--host=<replaceable class="parameter">host</replaceable></option></term>
<listitem>
<para>
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 <envar>PGHOST</envar> environment variable, if set,
else a Unix domain socket connection is attempted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-p <replaceable class="parameter">port</replaceable></option></term>
<term><option>--port=<replaceable class="parameter">port</replaceable></option></term>
<listitem>
<para>
Specifies the TCP port or local Unix domain socket file
extension on which the server is listening for connections.
Defaults to the <envar>PGPORT</envar> environment variable, if
set, or a compiled-in default.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-U <replaceable>username</replaceable></option></term>
<term><option>--username=<replaceable class="parameter">username</replaceable></option></term>
<listitem>
<para>
User name to connect as.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-w</option></term>
<term><option>--no-password</option></term>
<listitem>
<para>
Never issue a password prompt. If the server requires
password authentication and a password is not available by
other means such as a <filename>.pgpass</filename> 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-W</option></term>
<term><option>--password</option></term>
<listitem>
<para>
Force <application>pg_receivewal</application> to prompt for a
password before connecting to a database.
</para>
<para>
This option is never essential, since
<application>pg_receivewal</application> will automatically prompt
for a password if the server demands password authentication.
However, <application>pg_receivewal</application> will waste a
connection attempt finding out that the server wants a password.
In some cases it is worth typing <option>-W</option> to avoid the extra
connection attempt.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
<application>pg_receivewal</application> can perform one of the two
following actions in order to control physical replication slots:
<variablelist>
<varlistentry>
<term><option>--create-slot</option></term>
<listitem>
<para>
Create a new physical replication slot with the name specified in
<option>--slot</option>, then exit.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--drop-slot</option></term>
<listitem>
<para>
Drop the replication slot with the name specified in
<option>--slot</option>, then exit.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
Other options are also available:
<variablelist>
<varlistentry>
<term><option>-V</option></term>
<term><option>--version</option></term>
<listitem>
<para>
Print the <application>pg_receivewal</application> version and exit.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-?</option></term>
<term><option>--help</option></term>
<listitem>
<para>
Show help about <application>pg_receivewal</application> command line
arguments, and exit.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1>
<title>Exit Status</title>
<para>
<application>pg_receivewal</application> will exit with status 0 when
terminated by the <systemitem>SIGINT</systemitem> or
<systemitem>SIGTERM</systemitem> 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.
</para>
</refsect1>
<refsect1>
<title>Environment</title>
<para>
This utility, like most other <productname>PostgreSQL</productname> utilities,
uses the environment variables supported by <application>libpq</application>
(see <xref linkend="libpq-envars"/>).
</para>
Unified logging system for command-line programs This unifies the various ad hoc logging (message printing, error printing) systems used throughout the command-line programs. Features: - Program name is automatically prefixed. - Message string does not end with newline. This removes a common source of inconsistencies and omissions. - Additionally, a final newline is automatically stripped, simplifying use of PQerrorMessage() etc., another common source of mistakes. - I converted error message strings to use %m where possible. - As a result of the above several points, more translatable message strings can be shared between different components and between frontends and backend, without gratuitous punctuation or whitespace differences. - There is support for setting a "log level". This is not meant to be user-facing, but can be used internally to implement debug or verbose modes. - Lazy argument evaluation, so no significant overhead if logging at some level is disabled. - Some color in the messages, similar to gcc and clang. Set PG_COLOR=auto to try it out. Some colors are predefined, but can be customized by setting PG_COLORS. - Common files (common/, fe_utils/, etc.) can handle logging much more simply by just using one API without worrying too much about the context of the calling program, requiring callbacks, or having to pass "progname" around everywhere. - Some programs called setvbuf() to make sure that stderr is unbuffered, even on Windows. But not all programs did that. This is now done centrally. Soft goals: - Reduces vertical space use and visual complexity of error reporting in the source code. - Encourages more deliberate classification of messages. For example, in some cases it wasn't clear without analyzing the surrounding code whether a message was meant as an error or just an info. - Concepts and terms are vaguely aligned with popular logging frameworks such as log4j and Python logging. This is all just about printing stuff out. Nothing affects program flow (e.g., fatal exits). The uses are just too varied to do that. Some existing code had wrappers that do some kind of print-and-exit, and I adapted those. I tried to keep the output mostly the same, but there is a lot of historical baggage to unwind and special cases to consider, and I might not always have succeeded. One significant change is that pg_rewind used to write all error messages to stdout. That is now changed to stderr. Reviewed-by: Donald Dong <xdong@csumb.edu> Reviewed-by: Arthur Zakirov <a.zakirov@postgrespro.ru> Discussion: https://www.postgresql.org/message-id/flat/6a609b43-4f57-7348-6480-bd022f924310@2ndquadrant.com
2019-04-01 14:24:37 +02:00
<para>
The environment variable <envar>PG_COLOR</envar> specifies whether to use
color in diagnostic messages. Possible values are
<literal>always</literal>, <literal>auto</literal> and
Unified logging system for command-line programs This unifies the various ad hoc logging (message printing, error printing) systems used throughout the command-line programs. Features: - Program name is automatically prefixed. - Message string does not end with newline. This removes a common source of inconsistencies and omissions. - Additionally, a final newline is automatically stripped, simplifying use of PQerrorMessage() etc., another common source of mistakes. - I converted error message strings to use %m where possible. - As a result of the above several points, more translatable message strings can be shared between different components and between frontends and backend, without gratuitous punctuation or whitespace differences. - There is support for setting a "log level". This is not meant to be user-facing, but can be used internally to implement debug or verbose modes. - Lazy argument evaluation, so no significant overhead if logging at some level is disabled. - Some color in the messages, similar to gcc and clang. Set PG_COLOR=auto to try it out. Some colors are predefined, but can be customized by setting PG_COLORS. - Common files (common/, fe_utils/, etc.) can handle logging much more simply by just using one API without worrying too much about the context of the calling program, requiring callbacks, or having to pass "progname" around everywhere. - Some programs called setvbuf() to make sure that stderr is unbuffered, even on Windows. But not all programs did that. This is now done centrally. Soft goals: - Reduces vertical space use and visual complexity of error reporting in the source code. - Encourages more deliberate classification of messages. For example, in some cases it wasn't clear without analyzing the surrounding code whether a message was meant as an error or just an info. - Concepts and terms are vaguely aligned with popular logging frameworks such as log4j and Python logging. This is all just about printing stuff out. Nothing affects program flow (e.g., fatal exits). The uses are just too varied to do that. Some existing code had wrappers that do some kind of print-and-exit, and I adapted those. I tried to keep the output mostly the same, but there is a lot of historical baggage to unwind and special cases to consider, and I might not always have succeeded. One significant change is that pg_rewind used to write all error messages to stdout. That is now changed to stderr. Reviewed-by: Donald Dong <xdong@csumb.edu> Reviewed-by: Arthur Zakirov <a.zakirov@postgrespro.ru> Discussion: https://www.postgresql.org/message-id/flat/6a609b43-4f57-7348-6480-bd022f924310@2ndquadrant.com
2019-04-01 14:24:37 +02:00
<literal>never</literal>.
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
When using <application>pg_receivewal</application> instead of
<xref linkend="guc-archive-command"/> or
<xref linkend="guc-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 <xref linkend="guc-archive-command"/> or
<xref linkend="guc-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.
</para>
<para>
<application>pg_receivewal</application> will preserve group permissions on
the received WAL files if group permissions are enabled on the source
cluster.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
To stream the write-ahead log from the server at
<literal>mydbserver</literal> and store it in the local directory
<filename>/usr/local/pgsql/archive</filename>:
<screen>
<prompt>$</prompt> <userinput>pg_receivewal -h mydbserver -D /usr/local/pgsql/archive</userinput>
</screen></para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="app-pgbasebackup"/></member>
</simplelist>
</refsect1>
</refentry>