On Mon, Jan 23, 2023 at 01:44:28PM -0800, Nathan Bossart wrote: > On Mon, Jan 23, 2023 at 11:44:57AM +0900, Michael Paquier wrote: > I updated the documentation as you suggested, and I renamed basic_archive > to basic_wal_module.
Thanks. The renaming of basic_archive to basic_wal_module looked
fine, so applied.
While looking at the docs, I found a bit confusing that the main
section of the WAL modules included the full description for the
archive modules, so I have moved that into the sect2 dedicated to the
archive modules instead, as of the attached. 0004 has been updated in
consequence, with details about the recovery bits within its own
sect2.
>> (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
>> - errmsg("must specify restore_command when standby mode is not
>> enabled")));
>> + errmsg("must specify restore_command or a restore_library that defines
>> "
>> + "a restore callback when standby mode is not enabled")));
>> This is long. Shouldn't this be split into an errdetail() to list all
>> the options at hand?
>
> Should the errmsg() be something like "recovery parameters misconfigured"?
Hmm. Here is an idea:
- errmsg: "must specify restore option when standby mode is not enabled"
- errdetail: "Either restore_command or restore_library need to be
specified."
>> - if (XLogArchiveLibrary[0] != '\0' && XLogArchiveCommand[0] != '\0')
>> - ereport(ERROR,
>> - (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
>> - errmsg("both archive_command and archive_library set"),
>> - errdetail("Only one of archive_command, archive_library may
>> be set.")));
>> + CheckMutuallyExclusiveGUCs(XLogArchiveLibrary, "archive_library",
>> + XLogArchiveCommand, "archive_command");
>>
>> The introduction of this routine could be a patch on its own, as it
>> impacts the archiving path.
>
> I moved this to a separate patch.
While pondering about that, I found a bit sad that this only works for
string GUCs, while it could be possible to do the same kind of checks
for the other GUC types with a more generic routine? Not enum,
obviously, but int, float, bool and real, with the a failure if both
GUCs are set to non-default values? Also, and I may be missing
something here, do we really need to pass the value of the parameters
to check? Wouldn't it be enough to check for the case where both
parameters are set to their non-default values after reloading?
>> - Startup reloading, as of StartupRereadConfig(). This code could
>> involve a WAL receiver restart depending on a change in the slot
>> change or in primary_conninfo, and force at the same time an ERROR
>> because of conflicting recovery library and command configuration.
>> This one should be safe because pendingWalRcvRestart would just be
>> considered later on by the startup process itself while waiting for
>> WAL to become available. Still this could deserve a comment? Even if
>> there is a misconfiguration, a reload on a standby would enforce a
>> FATAL in the startup process, taking down the whole server.
>
> Do you think the parameter checks should go before the WAL receiver restart
> logic?
Yeah, switching the order makes the logic more robust IMO.
>> - Checkpointer initialization, as of CheckpointerMain(). A
>> configuration failure in this code path, aka server startup, causes
>> the server to loop infinitely on FATAL with the misconfiguration
>> showing up all the time.. This is a problem.
>
> Perhaps this is a reason to move the parameter check in CheckpointerMain()
> to after the sigsetjmp() block. This should avoid full server restarts.
> Only the checkpointer process would loop with the ERROR.
The loop part is annoying.. I've never been a fan of adding this
cross-value checks for the archiver modules in the first place, and it
would make things much simpler in the checkpointer if we need to think
about that as we want these values to be reloadable. Perhaps this
could just be an exception where we just give priority on one over the
other archive_cleanup_command? The startup process has a well-defined
sequence after a failure, while the checkpointer is designed to remain
robust.
>> - Last comes the checkpointer GUC reloading, as of
>> HandleCheckpointerInterrupts(), with a second problem. This
>> introduces a failure path where ConfigReloadPending is processed at
>> the same time as ShutdownRequestPending based on the way it is coded,
>> interacting with what would be a normal shutdown in some cases? And
>> actually, if you enforce a misconfiguration on reload, the
>> checkpointer reports an error but it does not enforce a process
>> restart, hence it keeps around the new, incorrect, configuration while
>> waiting for a new checkpoint to happen once restore_library and
>> archive_cleanup_command are set. This could lead to surprises, IMO.
>> Upgrading to a FATAL in this code path triggers an infinite loop, like
>> the startup path.
>
> If we move the parameter check in CheckpointerMain() as described above,
> the checkpointer should be unable to proceed with an incorrect
> configuration. For the normal shutdown part, do you think the
> ShutdownRequestPending block should be moved to before the
> ConfigReloadPending block in HandleCheckpointerInterrupts()?
I would not touch this order. This could influence the setup a
shutdown checkpoint relies on, for one.
>> If the archive_cleanup_command ballback of a restore library triggers
>> a FATAL, it seems to me that it would continuously trigger a server
>> restart, actually. Perhaps that's something to document, in
>> comparison to the safe fallbacks of the shell command where we don't
>> force an ERROR to give priority to the stability of the checkpointer.
>
> I'm not sure it's worth documenting that ereport(FATAL, ...) in the
> checkpointer process will cause a server restart. In most cases, an
> extension author would use ERROR, which, if we make the aforementioned
> changes, would at most cause the checkpointer to effectively restart. This
> is similar to archive modules where an ERROR causes only the archiver
> process to restart. Also, we document that recovery libraries are loaded
> in the startup and checkpointer processes, so IMO it should be relatively
> apparent that doing something like FATAL or proc_exit() is bad.
Okay. Fine by me. This could always be amended later, as required.
+ if (recoveryRestoreCommand[0] == '\0')
+ RecoveryContext.restore_cb = NULL;
+ if (archiveCleanupCommand[0] == '\0')
+ RecoveryContext.archive_cleanup_cb = NULL;
+ if (recoveryEndCommand[0] == '\0')
+ RecoveryContext.recovery_end_cb = NULL;
Could it be cleaner to put this knowledge directly in shell_restore.c
with a fast-exit path after entering each callback? It does not
strike me as a good thing to sprinkle more than necessary the
knowledge about the commands.
Another question that popped in my mind: could it be better to have
two different shutdown callbacks for the checkpointer and the startup
process? Having some tests for both, like shell_archive.c, would be
nice, actually.
--
Michael
From 7d4425744e2bc96418d6ef85c9408bed9e91aa9b Mon Sep 17 00:00:00 2001
From: Michael Paquier <mich...@paquier.xyz>
Date: Wed, 25 Jan 2023 15:39:23 +0900
Subject: [PATCH v11 1/3] doc: Refactor the chapter related to archive modules
to be WAL modules
Archive modules are now a subsection of this more generic section, and
recovery modules would be a second subsection of it.
---
doc/src/sgml/archive-modules.sgml | 136 --------------------------
doc/src/sgml/backup.sgml | 2 +-
doc/src/sgml/basic-wal-module.sgml | 2 +-
doc/src/sgml/config.sgml | 2 +-
doc/src/sgml/filelist.sgml | 2 +-
doc/src/sgml/postgres.sgml | 2 +-
doc/src/sgml/system-views.sgml | 2 +-
doc/src/sgml/wal-modules.sgml | 149 +++++++++++++++++++++++++++++
8 files changed, 155 insertions(+), 142 deletions(-)
delete mode 100644 doc/src/sgml/archive-modules.sgml
create mode 100644 doc/src/sgml/wal-modules.sgml
diff --git a/doc/src/sgml/archive-modules.sgml b/doc/src/sgml/archive-modules.sgml
deleted file mode 100644
index 1a32006e2c..0000000000
--- a/doc/src/sgml/archive-modules.sgml
+++ /dev/null
@@ -1,136 +0,0 @@
-<!-- doc/src/sgml/archive-modules.sgml -->
-
-<chapter id="archive-modules">
- <title>Archive Modules</title>
- <indexterm zone="archive-modules">
- <primary>Archive Modules</primary>
- </indexterm>
-
- <para>
- PostgreSQL provides infrastructure to create custom modules for continuous
- archiving (see <xref linkend="continuous-archiving"/>). While archiving via
- a shell command (i.e., <xref linkend="guc-archive-command"/>) is much
- simpler, a custom archive module will often be considerably more robust and
- performant.
- </para>
-
- <para>
- When a custom <xref linkend="guc-archive-library"/> is configured, PostgreSQL
- will submit completed WAL files to the module, and the server will avoid
- recycling or removing these WAL files until the module indicates that the files
- were successfully archived. It is ultimately up to the module to decide what
- to do with each WAL file, but many recommendations are listed at
- <xref linkend="backup-archiving-wal"/>.
- </para>
-
- <para>
- Archiving modules must at least consist of an initialization function (see
- <xref linkend="archive-module-init"/>) and the required callbacks (see
- <xref linkend="archive-module-callbacks"/>). However, archive modules are
- also permitted to do much more (e.g., declare GUCs and register background
- workers).
- </para>
-
- <para>
- The <filename>contrib/basic_wal_module</filename> module contains a working
- example, which demonstrates some useful techniques.
- </para>
-
- <sect1 id="archive-module-init">
- <title>Initialization Functions</title>
- <indexterm zone="archive-module-init">
- <primary>_PG_archive_module_init</primary>
- </indexterm>
- <para>
- An archive library is loaded by dynamically loading a shared library with the
- <xref linkend="guc-archive-library"/>'s name as the library base name. The
- normal library search path is used to locate the library. To provide the
- required archive module callbacks and to indicate that the library is
- actually an archive module, it needs to provide a function named
- <function>_PG_archive_module_init</function>. This function is passed a
- struct that needs to be filled with the callback function pointers for
- individual actions.
-
-<programlisting>
-typedef struct ArchiveModuleCallbacks
-{
- ArchiveCheckConfiguredCB check_configured_cb;
- ArchiveFileCB archive_file_cb;
- ArchiveShutdownCB shutdown_cb;
-} ArchiveModuleCallbacks;
-typedef void (*ArchiveModuleInit) (struct ArchiveModuleCallbacks *cb);
-</programlisting>
-
- Only the <function>archive_file_cb</function> callback is required. The
- others are optional.
- </para>
- </sect1>
-
- <sect1 id="archive-module-callbacks">
- <title>Archive Module Callbacks</title>
- <para>
- The archive callbacks define the actual archiving behavior of the module.
- The server will call them as required to process each individual WAL file.
- </para>
-
- <sect2 id="archive-module-check">
- <title>Check Callback</title>
- <para>
- The <function>check_configured_cb</function> callback is called to determine
- whether the module is fully configured and ready to accept WAL files (e.g.,
- its configuration parameters are set to valid values). If no
- <function>check_configured_cb</function> is defined, the server always
- assumes the module is configured.
-
-<programlisting>
-typedef bool (*ArchiveCheckConfiguredCB) (void);
-</programlisting>
-
- If <literal>true</literal> is returned, the server will proceed with
- archiving the file by calling the <function>archive_file_cb</function>
- callback. If <literal>false</literal> is returned, archiving will not
- proceed, and the archiver will emit the following message to the server log:
-<screen>
-WARNING: archive_mode enabled, yet archiving is not configured
-</screen>
- In the latter case, the server will periodically call this function, and
- archiving will proceed only when it returns <literal>true</literal>.
- </para>
- </sect2>
-
- <sect2 id="archive-module-archive">
- <title>Archive Callback</title>
- <para>
- The <function>archive_file_cb</function> callback is called to archive a
- single WAL file.
-
-<programlisting>
-typedef bool (*ArchiveFileCB) (const char *file, const char *path);
-</programlisting>
-
- If <literal>true</literal> is returned, the server proceeds as if the file
- was successfully archived, which may include recycling or removing the
- original WAL file. If <literal>false</literal> is returned, the server will
- keep the original WAL file and retry archiving later.
- <replaceable>file</replaceable> will contain just the file name of the WAL
- file to archive, while <replaceable>path</replaceable> contains the full
- path of the WAL file (including the file name).
- </para>
- </sect2>
-
- <sect2 id="archive-module-shutdown">
- <title>Shutdown Callback</title>
- <para>
- The <function>shutdown_cb</function> callback is called when the archiver
- process exits (e.g., after an error) or the value of
- <xref linkend="guc-archive-library"/> changes. If no
- <function>shutdown_cb</function> is defined, no special action is taken in
- these situations.
-
-<programlisting>
-typedef void (*ArchiveShutdownCB) (void);
-</programlisting>
- </para>
- </sect2>
- </sect1>
-</chapter>
diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml
index be05a33205..12d9bb3f81 100644
--- a/doc/src/sgml/backup.sgml
+++ b/doc/src/sgml/backup.sgml
@@ -660,7 +660,7 @@ test ! -f /mnt/server/archivedir/00000001000000A900000065 && cp pg_wal/0
than writing a shell command. However, archive modules can be more
performant than archiving via shell, and they will have access to many
useful server resources. For more information about archive modules, see
- <xref linkend="archive-modules"/>.
+ <xref linkend="wal-modules"/>.
</para>
<para>
diff --git a/doc/src/sgml/basic-wal-module.sgml b/doc/src/sgml/basic-wal-module.sgml
index c418b01eb8..f972566374 100644
--- a/doc/src/sgml/basic-wal-module.sgml
+++ b/doc/src/sgml/basic-wal-module.sgml
@@ -12,7 +12,7 @@
This module copies completed WAL segment files to the specified directory.
This may not be especially useful, but it can serve as a starting point for
developing your own archive module. For more information about archive
- modules, see <xref linkend="archive-modules"/>.
+ modules, see <xref linkend="wal-modules"/>.
</para>
<para>
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index f985afc009..bba24bdcb8 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3666,7 +3666,7 @@ include_dir 'conf.d'
shared library is used for archiving. The WAL archiver process is
restarted by the postmaster when this parameter changes. For more
information, see <xref linkend="backup-archiving-wal"/> and
- <xref linkend="archive-modules"/>.
+ <xref linkend="wal-modules"/>.
</para>
<para>
This parameter can only be set in the
diff --git a/doc/src/sgml/filelist.sgml b/doc/src/sgml/filelist.sgml
index 2d36c34ce8..31b4dc8fba 100644
--- a/doc/src/sgml/filelist.sgml
+++ b/doc/src/sgml/filelist.sgml
@@ -100,7 +100,7 @@
<!ENTITY custom-scan SYSTEM "custom-scan.sgml">
<!ENTITY logicaldecoding SYSTEM "logicaldecoding.sgml">
<!ENTITY replication-origins SYSTEM "replication-origins.sgml">
-<!ENTITY archive-modules SYSTEM "archive-modules.sgml">
+<!ENTITY wal-modules SYSTEM "wal-modules.sgml">
<!ENTITY protocol SYSTEM "protocol.sgml">
<!ENTITY sources SYSTEM "sources.sgml">
<!ENTITY storage SYSTEM "storage.sgml">
diff --git a/doc/src/sgml/postgres.sgml b/doc/src/sgml/postgres.sgml
index 2e271862fc..817e774155 100644
--- a/doc/src/sgml/postgres.sgml
+++ b/doc/src/sgml/postgres.sgml
@@ -233,7 +233,7 @@ break is not needed in a wider output rendering.
&bgworker;
&logicaldecoding;
&replication-origins;
- &archive-modules;
+ &wal-modules;
</part>
diff --git a/doc/src/sgml/system-views.sgml b/doc/src/sgml/system-views.sgml
index 7c8fc3f654..e93e733051 100644
--- a/doc/src/sgml/system-views.sgml
+++ b/doc/src/sgml/system-views.sgml
@@ -3351,7 +3351,7 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
<xref linkend="guc-shared-preload-libraries"/>,
a call to a C function in the extension, or the
<link linkend="sql-load"><command>LOAD</command></link> command).
- For example, since <link linkend="archive-modules">archive modules</link>
+ For example, since <link linkend="wal-modules">archive modules</link>
are normally loaded only by the archiver process not regular sessions,
this view will not display any customized options defined by such modules
unless special action is taken to load them into the backend process
diff --git a/doc/src/sgml/wal-modules.sgml b/doc/src/sgml/wal-modules.sgml
new file mode 100644
index 0000000000..283bba782d
--- /dev/null
+++ b/doc/src/sgml/wal-modules.sgml
@@ -0,0 +1,149 @@
+<!-- doc/src/sgml/wal-modules.sgml -->
+
+<chapter id="wal-modules">
+ <title>Write-Ahead Log Modules</title>
+ <indexterm zone="wal-modules">
+ <primary>Write-Ahead Log Modules</primary>
+ </indexterm>
+
+ <para>
+ This chapter provides general information about writing WAL modules, related
+ to the manipulation of WAL segments by the backend.
+ </para>
+
+ <sect1 id="archive-modules">
+ <title>Archive Modules</title>
+ <indexterm zone="archive-modules">
+ <primary>Archive Modules</primary>
+ </indexterm>
+
+ <para>
+ PostgreSQL provides infrastructure to create custom modules for continuous
+ archiving (see <xref linkend="continuous-archiving"/>). While archiving via
+ a shell command (i.e., <xref linkend="guc-archive-command"/>) is much
+ simpler, a custom WAL module will often be considerably more robust and
+ performant.
+ </para>
+
+ <para>
+ When a custom <xref linkend="guc-archive-library"/> is configured, PostgreSQL
+ will submit completed WAL files to the module, and the server will avoid
+ recycling or removing these WAL files until the module indicates that the
+ files were successfully archived. It is ultimately up to the module to
+ decide what to do with each WAL file, but many recommendations are listed at
+ <xref linkend="backup-archiving-wal"/>.
+ </para>
+
+ <para>
+ Archiving modules must at least consist of an initialization function (see
+ <xref linkend="archive-module-init"/>) and the required callbacks (see
+ <xref linkend="archive-module-callbacks"/>). However, archive modules are
+ also permitted to do much more (e.g., declare GUCs and register background
+ workers).
+ </para>
+
+ <para>
+ The <filename>contrib/basic_archive</filename> module contains a working
+ example, which demonstrates some useful techniques.
+ </para>
+
+ <sect2 id="archive-module-init">
+ <title>Initialization Functions</title>
+ <indexterm zone="archive-module-init">
+ <primary>_PG_archive_module_init</primary>
+ </indexterm>
+ <para>
+ An archive library is loaded by dynamically loading a shared library with
+ the <xref linkend="guc-archive-library"/>'s name as the library base name.
+ The normal library search path is used to locate the library. To provide
+ the required archive module callbacks and to indicate that the library is
+ actually an archive module, it needs to provide a function named
+ <function>_PG_archive_module_init</function>. This function is passed a
+ struct that needs to be filled with the callback function pointers for
+ individual actions.
+
+<programlisting>
+typedef struct ArchiveModuleCallbacks
+{
+ ArchiveCheckConfiguredCB check_configured_cb;
+ ArchiveFileCB archive_file_cb;
+ ArchiveShutdownCB shutdown_cb;
+} ArchiveModuleCallbacks;
+typedef void (*ArchiveModuleInit) (struct ArchiveModuleCallbacks *cb);
+</programlisting>
+
+ Only the <function>archive_file_cb</function> callback is required. The
+ others are optional.
+ </para>
+ </sect2>
+
+ <sect2 id="archive-module-callbacks">
+ <title>Archive Module Callbacks</title>
+ <para>
+ The archive callbacks define the actual archiving behavior of the module.
+ The server will call them as required to process each individual WAL file.
+ </para>
+
+ <sect3 id="archive-module-check">
+ <title>Check Callback</title>
+ <para>
+ The <function>check_configured_cb</function> callback is called to
+ determine whether the module is fully configured and ready to accept WAL
+ files (e.g., its configuration parameters are set to valid values). If no
+ <function>check_configured_cb</function> is defined, the server always
+ assumes the module is configured.
+
+<programlisting>
+typedef bool (*ArchiveCheckConfiguredCB) (void);
+</programlisting>
+
+ If <literal>true</literal> is returned, the server will proceed with
+ archiving the file by calling the <function>archive_file_cb</function>
+ callback. If <literal>false</literal> is returned, archiving will not
+ proceed, and the archiver will emit the following message to the server
+ log:
+<screen>
+WARNING: archive_mode enabled, yet archiving is not configured
+</screen>
+ In the latter case, the server will periodically call this function, and
+ archiving will proceed only when it returns <literal>true</literal>.
+ </para>
+ </sect3>
+
+ <sect3 id="archive-module-archive">
+ <title>Archive Callback</title>
+ <para>
+ The <function>archive_file_cb</function> callback is called to archive a
+ single WAL file.
+
+<programlisting>
+typedef bool (*ArchiveFileCB) (const char *file, const char *path);
+</programlisting>
+
+ If <literal>true</literal> is returned, the server proceeds as if the file
+ was successfully archived, which may include recycling or removing the
+ original WAL file. If <literal>false</literal> is returned, the server
+ will keep the original WAL file and retry archiving later.
+ <replaceable>file</replaceable> will contain just the file name of the WAL
+ file to archive, while <replaceable>path</replaceable> contains the full
+ path of the WAL file (including the file name).
+ </para>
+ </sect3>
+
+ <sect3 id="archive-module-shutdown">
+ <title>Shutdown Callback</title>
+ <para>
+ The <function>shutdown_cb</function> callback is called when the archiver
+ process exits (e.g., after an error) or the value of
+ <xref linkend="guc-archive-library"/> changes. If no
+ <function>shutdown_cb</function> is defined, no special action is taken in
+ these situations.
+
+<programlisting>
+typedef void (*ArchiveShutdownCB) (void);
+</programlisting>
+ </para>
+ </sect3>
+ </sect2>
+ </sect1>
+</chapter>
--
2.39.0
From f6caa58074a6dd66c57f2e8a1ff36e9fbe6530b9 Mon Sep 17 00:00:00 2001
From: Michael Paquier <mich...@paquier.xyz>
Date: Wed, 25 Jan 2023 15:54:35 +0900
Subject: [PATCH v11 2/3] introduce routine for checking mutually exclusive
parameters
---
src/include/utils/guc.h | 2 ++
src/backend/postmaster/pgarch.c | 7 ++-----
src/backend/utils/misc/guc.c | 18 ++++++++++++++++++
3 files changed, 22 insertions(+), 5 deletions(-)
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index ba89d013e6..d7785785c2 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -372,6 +372,8 @@ extern int NewGUCNestLevel(void);
extern void AtEOXact_GUC(bool isCommit, int nestLevel);
extern void BeginReportingGUCOptions(void);
extern void ReportChangedGUCOptions(void);
+extern void CheckMutuallyExclusiveGUCs(const char *p1val, const char *p1name,
+ const char *p2val, const char *p2name);
extern void ParseLongOption(const char *string, char **name, char **value);
extern const char *get_config_unit_name(int flags);
extern bool parse_int(const char *value, int *result, int flags,
diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index 8ecdb9ca23..8e91f2d70f 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -831,11 +831,8 @@ LoadArchiveLibrary(void)
{
ArchiveModuleInit archive_init;
- if (XLogArchiveLibrary[0] != '\0' && XLogArchiveCommand[0] != '\0')
- ereport(ERROR,
- (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
- errmsg("both archive_command and archive_library set"),
- errdetail("Only one of archive_command, archive_library may be set.")));
+ CheckMutuallyExclusiveGUCs(XLogArchiveLibrary, "archive_library",
+ XLogArchiveCommand, "archive_command");
memset(&ArchiveContext, 0, sizeof(ArchiveModuleCallbacks));
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index d52069f446..e63515d624 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2558,6 +2558,24 @@ ReportChangedGUCOptions(void)
}
}
+/*
+ * Check if two GUCs are mutually set. Works only when comparing two
+ * string GUCs.
+ *
+ * ERROR if both parameters are set.
+ */
+void
+CheckMutuallyExclusiveGUCs(const char *p1val, const char *p1name,
+ const char *p2val, const char *p2name)
+{
+ if (p1val[0] != '\0' && p2val[0] != '\0')
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("cannot set both %s and %s", p1name, p2name),
+ errdetail("Only one of %s or %s may be set.",
+ p1name, p2name)));
+}
+
/*
* ReportGUCOption: if appropriate, transmit option value to frontend
*
--
2.39.0
From 52407882dee0751807f528bc785925a49e88749d Mon Sep 17 00:00:00 2001
From: Michael Paquier <mich...@paquier.xyz>
Date: Wed, 25 Jan 2023 16:27:43 +0900
Subject: [PATCH v11 3/3] introduce restore_library
---
src/include/access/xlog_internal.h | 1 +
src/include/access/xlogarchive.h | 44 ++++-
src/include/access/xlogrecovery.h | 1 +
src/backend/access/transam/shell_restore.c | 21 ++-
src/backend/access/transam/xlog.c | 12 +-
src/backend/access/transam/xlogarchive.c | 70 ++++++-
src/backend/access/transam/xlogrecovery.c | 26 ++-
src/backend/postmaster/checkpointer.c | 26 +++
src/backend/postmaster/startup.c | 23 ++-
src/backend/utils/misc/guc_tables.c | 10 +
src/backend/utils/misc/postgresql.conf.sample | 1 +
doc/src/sgml/backup.sgml | 43 ++++-
doc/src/sgml/basic-wal-module.sgml | 33 ++--
doc/src/sgml/config.sgml | 53 +++++-
doc/src/sgml/high-availability.sgml | 23 ++-
doc/src/sgml/wal-modules.sgml | 171 +++++++++++++++++-
contrib/basic_wal_module/Makefile | 2 +
contrib/basic_wal_module/basic_wal_module.c | 69 ++++++-
contrib/basic_wal_module/meson.build | 5 +
contrib/basic_wal_module/t/001_restore.pl | 44 +++++
20 files changed, 615 insertions(+), 63 deletions(-)
create mode 100644 contrib/basic_wal_module/t/001_restore.pl
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 59fc7bc105..756f0898b5 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -400,5 +400,6 @@ extern PGDLLIMPORT bool ArchiveRecoveryRequested;
extern PGDLLIMPORT bool InArchiveRecovery;
extern PGDLLIMPORT bool StandbyMode;
extern PGDLLIMPORT char *recoveryRestoreCommand;
+extern PGDLLIMPORT char *restoreLibrary;
#endif /* XLOG_INTERNAL_H */
diff --git a/src/include/access/xlogarchive.h b/src/include/access/xlogarchive.h
index 299304703e..71c9b88165 100644
--- a/src/include/access/xlogarchive.h
+++ b/src/include/access/xlogarchive.h
@@ -30,9 +30,45 @@ extern bool XLogArchiveIsReady(const char *xlog);
extern bool XLogArchiveIsReadyOrDone(const char *xlog);
extern void XLogArchiveCleanup(const char *xlog);
-extern bool shell_restore(const char *file, const char *path,
- const char *lastRestartPointFileName);
-extern void shell_archive_cleanup(const char *lastRestartPointFileName);
-extern void shell_recovery_end(const char *lastRestartPointFileName);
+/*
+ * Recovery module callbacks
+ *
+ * These callback functions should be defined by recovery libraries and
+ * returned via _PG_recovery_module_init(). For more information about the
+ * purpose of each callback, refer to the recovery modules documentation.
+ */
+typedef bool (*RecoveryRestoreCB) (const char *file, const char *path,
+ const char *lastRestartPointFileName);
+typedef void (*RecoveryArchiveCleanupCB) (const char *lastRestartPointFileName);
+typedef void (*RecoveryEndCB) (const char *lastRestartPointFileName);
+typedef void (*RecoveryShutdownCB) (void);
+
+typedef struct RecoveryModuleCallbacks
+{
+ RecoveryRestoreCB restore_cb;
+ RecoveryArchiveCleanupCB archive_cleanup_cb;
+ RecoveryEndCB recovery_end_cb;
+ RecoveryShutdownCB shutdown_cb;
+} RecoveryModuleCallbacks;
+
+extern RecoveryModuleCallbacks RecoveryContext;
+
+/*
+ * Type of the shared library symbol _PG_recovery_module_init that is looked up
+ * when loading a recovery library.
+ */
+typedef void (*RecoveryModuleInit) (RecoveryModuleCallbacks *cb);
+
+extern PGDLLEXPORT void _PG_recovery_module_init(RecoveryModuleCallbacks *cb);
+
+extern void LoadRecoveryCallbacks(void);
+extern void call_recovery_module_shutdown_cb(int code, Datum arg);
+
+/*
+ * Since the logic for recovery via a shell command is in the core server and
+ * does not need to be loaded via a shared library, it has a special
+ * initialization function.
+ */
+extern void shell_restore_init(RecoveryModuleCallbacks *cb);
#endif /* XLOG_ARCHIVE_H */
diff --git a/src/include/access/xlogrecovery.h b/src/include/access/xlogrecovery.h
index 47c29350f5..35d1d09374 100644
--- a/src/include/access/xlogrecovery.h
+++ b/src/include/access/xlogrecovery.h
@@ -55,6 +55,7 @@ extern PGDLLIMPORT int recovery_min_apply_delay;
extern PGDLLIMPORT char *PrimaryConnInfo;
extern PGDLLIMPORT char *PrimarySlotName;
extern PGDLLIMPORT char *recoveryRestoreCommand;
+extern PGDLLIMPORT char *restoreLibrary;
extern PGDLLIMPORT char *recoveryEndCommand;
extern PGDLLIMPORT char *archiveCleanupCommand;
diff --git a/src/backend/access/transam/shell_restore.c b/src/backend/access/transam/shell_restore.c
index 8458209f49..dfd409905c 100644
--- a/src/backend/access/transam/shell_restore.c
+++ b/src/backend/access/transam/shell_restore.c
@@ -4,7 +4,8 @@
* Recovery functions for a user-specified shell command.
*
* These recovery functions use a user-specified shell command (e.g. based
- * on the GUC restore_command).
+ * on the GUC restore_command). It is used as the default, but other
+ * modules may define their own recovery logic.
*
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
@@ -24,6 +25,10 @@
#include "storage/ipc.h"
#include "utils/wait_event.h"
+static bool shell_restore(const char *file, const char *path,
+ const char *lastRestartPointFileName);
+static void shell_archive_cleanup(const char *lastRestartPointFileName);
+static void shell_recovery_end(const char *lastRestartPointFileName);
static bool ExecuteRecoveryCommand(const char *command,
const char *commandName,
bool failOnSignal,
@@ -31,6 +36,16 @@ static bool ExecuteRecoveryCommand(const char *command,
uint32 wait_event_info,
int fail_elevel);
+void
+shell_restore_init(RecoveryModuleCallbacks *cb)
+{
+ AssertVariableIsOfType(&shell_restore_init, RecoveryModuleInit);
+
+ cb->restore_cb = shell_restore;
+ cb->archive_cleanup_cb = shell_archive_cleanup;
+ cb->recovery_end_cb = shell_recovery_end;
+}
+
/*
* Attempt to execute a shell-based restore command.
*
@@ -88,7 +103,7 @@ shell_restore(const char *file, const char *path,
/*
* Attempt to execute a shell-based archive cleanup command.
*/
-void
+static void
shell_archive_cleanup(const char *lastRestartPointFileName)
{
char *cmd;
@@ -104,7 +119,7 @@ shell_archive_cleanup(const char *lastRestartPointFileName)
/*
* Attempt to execute a shell-based end-of-recovery command.
*/
-void
+static void
shell_recovery_end(const char *lastRestartPointFileName)
{
char *cmd;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index fb4c860bde..47f7d2fcc1 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -4887,14 +4887,14 @@ CleanupAfterArchiveRecovery(TimeLineID EndOfLogTLI, XLogRecPtr EndOfLog,
TimeLineID newTLI)
{
/*
- * Execute the recovery_end_command, if any.
+ * Execute the recovery-end callback, if any.
*/
- if (recoveryEndCommand && strcmp(recoveryEndCommand, "") != 0)
+ if (RecoveryContext.recovery_end_cb)
{
char lastRestartPointFname[MAXFNAMELEN];
GetOldestRestartPointFileName(lastRestartPointFname);
- shell_recovery_end(lastRestartPointFname);
+ RecoveryContext.recovery_end_cb(lastRestartPointFname);
}
/*
@@ -7309,14 +7309,14 @@ CreateRestartPoint(int flags)
timestamptz_to_str(xtime)) : 0));
/*
- * Finally, execute archive_cleanup_command, if any.
+ * Execute the archive-cleanup callback, if any.
*/
- if (archiveCleanupCommand && strcmp(archiveCleanupCommand, "") != 0)
+ if (RecoveryContext.archive_cleanup_cb)
{
char lastRestartPointFname[MAXFNAMELEN];
GetOldestRestartPointFileName(lastRestartPointFname);
- shell_archive_cleanup(lastRestartPointFname);
+ RecoveryContext.archive_cleanup_cb(lastRestartPointFname);
}
return true;
diff --git a/src/backend/access/transam/xlogarchive.c b/src/backend/access/transam/xlogarchive.c
index 4b89addf97..4af5689c25 100644
--- a/src/backend/access/transam/xlogarchive.c
+++ b/src/backend/access/transam/xlogarchive.c
@@ -22,6 +22,8 @@
#include "access/xlog.h"
#include "access/xlog_internal.h"
#include "access/xlogarchive.h"
+#include "access/xlogrecovery.h"
+#include "fmgr.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/startup.h"
@@ -31,6 +33,11 @@
#include "storage/ipc.h"
#include "storage/lwlock.h"
+/*
+ * Global context for recovery-related callbacks.
+ */
+RecoveryModuleCallbacks RecoveryContext;
+
/*
* Attempt to retrieve the specified file from off-line archival storage.
* If successful, fill "path" with its complete path (note that this will be
@@ -70,7 +77,7 @@ RestoreArchivedFile(char *path, const char *xlogfname,
goto not_available;
/* In standby mode, restore_command might not be supplied */
- if (recoveryRestoreCommand == NULL || strcmp(recoveryRestoreCommand, "") == 0)
+ if (RecoveryContext.restore_cb == NULL)
goto not_available;
/*
@@ -148,14 +155,15 @@ RestoreArchivedFile(char *path, const char *xlogfname,
XLogFileName(lastRestartPointFname, 0, 0L, wal_segment_size);
/*
- * Check signals before restore command and reset afterwards.
+ * Check signals before restore callback and reset afterwards.
*/
PreRestoreCommand();
/*
* Copy xlog from archival storage to XLOGDIR
*/
- ret = shell_restore(xlogfname, xlogpath, lastRestartPointFname);
+ ret = RecoveryContext.restore_cb(xlogfname, xlogpath,
+ lastRestartPointFname);
PostRestoreCommand();
@@ -602,3 +610,59 @@ XLogArchiveCleanup(const char *xlog)
unlink(archiveStatusPath);
/* should we complain about failure? */
}
+
+/*
+ * Loads all the recovery callbacks into our global RecoveryContext. The
+ * caller is responsible for validating the combination of library/command
+ * parameters that are set (e.g., restore_command and restore_library cannot
+ * both be set).
+ */
+void
+LoadRecoveryCallbacks(void)
+{
+ RecoveryModuleInit init;
+
+ /*
+ * If the shell command is enabled, use our special initialization
+ * function. Otherwise, load the library and call its
+ * _PG_recovery_module_init().
+ */
+ if (restoreLibrary[0] == '\0')
+ init = shell_restore_init;
+ else
+ init = (RecoveryModuleInit)
+ load_external_function(restoreLibrary, "_PG_recovery_module_init",
+ false, NULL);
+
+ if (init == NULL)
+ ereport(ERROR,
+ (errmsg("recovery modules have to define the symbol "
+ "_PG_recovery_module_init")));
+
+ memset(&RecoveryContext, 0, sizeof(RecoveryModuleCallbacks));
+ (*init) (&RecoveryContext);
+
+ /*
+ * If using shell commands, remove callbacks for any commands that are not
+ * set.
+ */
+ if (restoreLibrary[0] == '\0')
+ {
+ if (recoveryRestoreCommand[0] == '\0')
+ RecoveryContext.restore_cb = NULL;
+ if (archiveCleanupCommand[0] == '\0')
+ RecoveryContext.archive_cleanup_cb = NULL;
+ if (recoveryEndCommand[0] == '\0')
+ RecoveryContext.recovery_end_cb = NULL;
+ }
+}
+
+/*
+ * Call the shutdown callback of the loaded recovery module, if defined.
+ */
+void
+call_recovery_module_shutdown_cb(int code, Datum arg)
+{
+ if (RecoveryContext.shutdown_cb)
+ RecoveryContext.shutdown_cb();
+}
diff --git a/src/backend/access/transam/xlogrecovery.c b/src/backend/access/transam/xlogrecovery.c
index 2a5352f879..04f94e4d53 100644
--- a/src/backend/access/transam/xlogrecovery.c
+++ b/src/backend/access/transam/xlogrecovery.c
@@ -80,6 +80,7 @@ const struct config_enum_entry recovery_target_action_options[] = {
/* options formerly taken from recovery.conf for archive recovery */
char *recoveryRestoreCommand = NULL;
+char *restoreLibrary = NULL;
char *recoveryEndCommand = NULL;
char *archiveCleanupCommand = NULL;
RecoveryTargetType recoveryTarget = RECOVERY_TARGET_UNSET;
@@ -1053,24 +1054,37 @@ validateRecoveryParameters(void)
if (!ArchiveRecoveryRequested)
return;
+ /*
+ * Check for invalid combinations of the command/library parameters and
+ * load the callbacks.
+ */
+ CheckMutuallyExclusiveGUCs(restoreLibrary, "restore_library",
+ recoveryRestoreCommand, "restore_command");
+ CheckMutuallyExclusiveGUCs(restoreLibrary, "restore_library",
+ recoveryEndCommand, "recovery_end_command");
+ before_shmem_exit(call_recovery_module_shutdown_cb, 0);
+ LoadRecoveryCallbacks();
+
/*
* Check for compulsory parameters
*/
if (StandbyModeRequested)
{
if ((PrimaryConnInfo == NULL || strcmp(PrimaryConnInfo, "") == 0) &&
- (recoveryRestoreCommand == NULL || strcmp(recoveryRestoreCommand, "") == 0))
+ RecoveryContext.restore_cb == NULL)
ereport(WARNING,
- (errmsg("specified neither primary_conninfo nor restore_command"),
- errhint("The database server will regularly poll the pg_wal subdirectory to check for files placed there.")));
+ (errmsg("specified neither primary_conninfo nor restore_command "
+ "nor a restore_library that defines a restore callback"),
+ errhint("The database server will regularly poll the pg_wal "
+ "subdirectory to check for files placed there.")));
}
else
{
- if (recoveryRestoreCommand == NULL ||
- strcmp(recoveryRestoreCommand, "") == 0)
+ if (RecoveryContext.restore_cb == NULL)
ereport(FATAL,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
- errmsg("must specify restore_command when standby mode is not enabled")));
+ errmsg("must specify restore_command or a restore_library that defines "
+ "a restore callback when standby mode is not enabled")));
}
/*
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index de0bbbfa79..6350fd0b83 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -38,6 +38,7 @@
#include "access/xlog.h"
#include "access/xlog_internal.h"
+#include "access/xlogarchive.h"
#include "access/xlogrecovery.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
@@ -222,6 +223,16 @@ CheckpointerMain(void)
*/
before_shmem_exit(pgstat_before_server_shutdown, 0);
+ /*
+ * Check for invalid combinations of the command/library parameters and
+ * load the callbacks. We do this before setting up the exception handler
+ * so that any problems result in a server crash shortly after startup.
+ */
+ CheckMutuallyExclusiveGUCs(restoreLibrary, "restore_library",
+ archiveCleanupCommand, "archive_cleanup_command");
+ before_shmem_exit(call_recovery_module_shutdown_cb, 0);
+ LoadRecoveryCallbacks();
+
/*
* Create a memory context that we will do all our work in. We do this so
* that we can reset the context during error recovery and thereby avoid
@@ -548,6 +559,9 @@ HandleCheckpointerInterrupts(void)
if (ConfigReloadPending)
{
+ char *prevRestoreLibrary = pstrdup(restoreLibrary);
+ char *prevArchiveCleanupCommand = pstrdup(archiveCleanupCommand);
+
ConfigReloadPending = false;
ProcessConfigFile(PGC_SIGHUP);
@@ -563,6 +577,18 @@ HandleCheckpointerInterrupts(void)
* because of SIGHUP.
*/
UpdateSharedMemoryConfig();
+
+ CheckMutuallyExclusiveGUCs(restoreLibrary, "restore_library",
+ archiveCleanupCommand, "archive_cleanup_command");
+ if (strcmp(prevRestoreLibrary, restoreLibrary) != 0 ||
+ strcmp(prevArchiveCleanupCommand, archiveCleanupCommand) != 0)
+ {
+ call_recovery_module_shutdown_cb(0, (Datum) 0);
+ LoadRecoveryCallbacks();
+ }
+
+ pfree(prevRestoreLibrary);
+ pfree(prevArchiveCleanupCommand);
}
if (ShutdownRequestPending)
{
diff --git a/src/backend/postmaster/startup.c b/src/backend/postmaster/startup.c
index 8786186898..f9ff2b5583 100644
--- a/src/backend/postmaster/startup.c
+++ b/src/backend/postmaster/startup.c
@@ -20,6 +20,7 @@
#include "postgres.h"
#include "access/xlog.h"
+#include "access/xlogarchive.h"
#include "access/xlogrecovery.h"
#include "access/xlogutils.h"
#include "libpq/pqsignal.h"
@@ -133,13 +134,17 @@ StartupProcShutdownHandler(SIGNAL_ARGS)
* Re-read the config file.
*
* If one of the critical walreceiver options has changed, flag xlog.c
- * to restart it.
+ * to restart it. Also, check for invalid combinations of the command/library
+ * parameters and reload the recovery callbacks if necessary.
*/
static void
StartupRereadConfig(void)
{
char *conninfo = pstrdup(PrimaryConnInfo);
char *slotname = pstrdup(PrimarySlotName);
+ char *prevRestoreLibrary = pstrdup(restoreLibrary);
+ char *prevRestoreCommand = pstrdup(recoveryRestoreCommand);
+ char *prevRecoveryEndCommand = pstrdup(recoveryEndCommand);
bool tempSlot = wal_receiver_create_temp_slot;
bool conninfoChanged;
bool slotnameChanged;
@@ -161,6 +166,22 @@ StartupRereadConfig(void)
if (conninfoChanged || slotnameChanged || tempSlotChanged)
StartupRequestWalReceiverRestart();
+
+ CheckMutuallyExclusiveGUCs(restoreLibrary, "restore_library",
+ recoveryRestoreCommand, "restore_command");
+ CheckMutuallyExclusiveGUCs(restoreLibrary, "restore_library",
+ recoveryEndCommand, "recovery_end_command");
+ if (strcmp(prevRestoreLibrary, restoreLibrary) != 0 ||
+ strcmp(prevRestoreCommand, recoveryRestoreCommand) != 0 ||
+ strcmp(prevRecoveryEndCommand, recoveryEndCommand) != 0)
+ {
+ call_recovery_module_shutdown_cb(0, (Datum) 0);
+ LoadRecoveryCallbacks();
+ }
+
+ pfree(prevRestoreLibrary);
+ pfree(prevRestoreCommand);
+ pfree(prevRecoveryEndCommand);
}
/* Handle various signals that might be sent to the startup process */
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 4ac808ed22..06d36513aa 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -3787,6 +3787,16 @@ struct config_string ConfigureNamesString[] =
NULL, NULL, NULL
},
+ {
+ {"restore_library", PGC_SIGHUP, WAL_ARCHIVE_RECOVERY,
+ gettext_noop("Sets the library that will be called for recovery actions."),
+ NULL
+ },
+ &restoreLibrary,
+ "",
+ NULL, NULL, NULL
+ },
+
{
{"archive_cleanup_command", PGC_SIGHUP, WAL_ARCHIVE_RECOVERY,
gettext_noop("Sets the shell command that will be executed at every restart point."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index d06074b86f..5641e5a3a8 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -270,6 +270,7 @@
# placeholders: %p = path of file to restore
# %f = file name only
# e.g. 'cp /mnt/server/archivedir/%f %p'
+#restore_library = '' # library to use for recovery actions
#archive_cleanup_command = '' # command to execute at every restartpoint
#recovery_end_command = '' # command to execute at completion of recovery
diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml
index 12d9bb3f81..19f79fd2f2 100644
--- a/doc/src/sgml/backup.sgml
+++ b/doc/src/sgml/backup.sgml
@@ -1180,9 +1180,27 @@ SELECT * FROM pg_backup_stop(wait_for_archive => true);
<para>
The key part of all this is to set up a recovery configuration that
describes how you want to recover and how far the recovery should
- run. The one thing that you absolutely must specify is the <varname>restore_command</varname>,
- which tells <productname>PostgreSQL</productname> how to retrieve archived
- WAL file segments. Like the <varname>archive_command</varname>, this is
+ run. The one thing that you absolutely must specify is either
+ <varname>restore_command</varname> or a <varname>restore_library</varname>
+ that defines a restore callback, which tells
+ <productname>PostgreSQL</productname> how to retrieve archived WAL file
+ segments.
+ </para>
+
+ <para>
+ Like the <varname>archive_library</varname> parameter,
+ <varname>restore_library</varname> is a shared library. Since such
+ libraries are written in <literal>C</literal>, creating your own may
+ require considerably more effort than writing a shell command. However,
+ recovery modules can be more performant than restoring via shell, and they
+ will have access to many useful server resources. For more information
+ about creating a <varname>restore_library</varname>, see
+ <xref linkend="wal-modules"/>.
+ </para>
+
+ <para>
+ Like the <varname>archive_command</varname>,
+ <varname>restore_command</varname> is
a shell command string. It can contain <literal>%f</literal>, which is
replaced by the name of the desired WAL file, and <literal>%p</literal>,
which is replaced by the path name to copy the WAL file to.
@@ -1201,14 +1219,20 @@ restore_command = 'cp /mnt/server/archivedir/%f %p'
</para>
<para>
- It is important that the command return nonzero exit status on failure.
- The command <emphasis>will</emphasis> be called requesting files that are not
- present in the archive; it must return nonzero when so asked. This is not
- an error condition. An exception is that if the command was terminated by
+ It is important that the <varname>restore_command</varname> return nonzero
+ exit status on failure, or, if you are using a
+ <varname>restore_library</varname>, that the restore function returns
+ <literal>false</literal> on failure. The command or library
+ <emphasis>will</emphasis> be called requesting files that are not
+ present in the archive; it must fail when so asked. This is not
+ an error condition. An exception is that if the
+ <varname>restore_command</varname> was terminated by
a signal (other than <systemitem>SIGTERM</systemitem>, which is used as
part of a database server shutdown) or an error by the shell (such as
command not found), then recovery will abort and the server will not start
- up.
+ up. Likewise, if the restore function provided by the
+ <varname>restore_library</varname> emits an <literal>ERROR</literal> or
+ <literal>FATAL</literal>, recovery will abort and the server won't start.
</para>
<para>
@@ -1232,7 +1256,8 @@ restore_command = 'cp /mnt/server/archivedir/%f %p'
close as possible given the available WAL segments). Therefore, a normal
recovery will end with a <quote>file not found</quote> message, the exact text
of the error message depending upon your choice of
- <varname>restore_command</varname>. You may also see an error message
+ <varname>restore_command</varname> or <varname>restore_library</varname>.
+ You may also see an error message
at the start of recovery for a file named something like
<filename>00000001.history</filename>. This is also normal and does not
indicate a problem in simple recovery situations; see
diff --git a/doc/src/sgml/basic-wal-module.sgml b/doc/src/sgml/basic-wal-module.sgml
index f972566374..ebb9f0d8c3 100644
--- a/doc/src/sgml/basic-wal-module.sgml
+++ b/doc/src/sgml/basic-wal-module.sgml
@@ -8,17 +8,20 @@
</indexterm>
<para>
- <filename>basic_wal_module</filename> is an example of an archive module.
- This module copies completed WAL segment files to the specified directory.
- This may not be especially useful, but it can serve as a starting point for
- developing your own archive module. For more information about archive
- modules, see <xref linkend="wal-modules"/>.
+ <filename>basic_wal_module</filename> is an example of a write-ahead log
+ module. This module copies completed WAL segment files to or from the
+ specified directory. This may not be especially useful, but it can serve as
+ a starting point for developing your own archive and recovery modules. For
+ more information about write-ahead log modules, see
+ <xref linkend="wal-modules"/>.
</para>
<para>
- In order to function, this module must be loaded via
+ For use as an archive module, this module must be loaded via
<xref linkend="guc-archive-library"/>, and <xref linkend="guc-archive-mode"/>
- must be enabled.
+ must be enabled. For use as a recovery module, this module must be loaded
+ via <xref linkend="guc-restore-library"/>, and recovery must be enabled (see
+ <xref linkend="runtime-config-wal-archive-recovery"/>).
</para>
<sect2 id="basic-wal-module-configuration-parameters">
@@ -34,11 +37,12 @@
</term>
<listitem>
<para>
- The directory where the server should copy WAL segment files. This
- directory must already exist. The default is an empty string, which
- effectively halts WAL archiving, but if <xref linkend="guc-archive-mode"/>
- is enabled, the server will accumulate WAL segment files in the
- expectation that a value will soon be provided.
+ The directory where the server should copy WAL segment files to or from.
+ This directory must already exist. The default is an empty string,
+ which, when used for archiving, effectively halts WAL archival, but if
+ <xref linkend="guc-archive-mode"/> is enabled, the server will accumulate
+ WAL segment files in the expectation that a value will soon be provided.
+ When an empty string is used for recovery, restore will fail.
</para>
</listitem>
</varlistentry>
@@ -46,7 +50,7 @@
<para>
These parameters must be set in <filename>postgresql.conf</filename>.
- Typical usage might be:
+ Typical usage as an archive module might be:
</para>
<programlisting>
@@ -61,7 +65,8 @@ basic_wal_module.archive_directory = '/path/to/archive/directory'
<title>Notes</title>
<para>
- Server crashes may leave temporary files with the prefix
+ When <filename>basic_wal_module</filename> is used as an archive module,
+ server crashes may leave temporary files with the prefix
<filename>archtemp</filename> in the archive directory. It is recommended to
delete such files before restarting the server after a crash. It is safe to
remove such files while the server is running as long as they are unrelated
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index bba24bdcb8..feb4ca34af 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3807,7 +3807,8 @@ include_dir 'conf.d'
recovery when the end of archived WAL is reached, but will keep trying to
continue recovery by connecting to the sending server as specified by the
<varname>primary_conninfo</varname> setting and/or by fetching new WAL
- segments using <varname>restore_command</varname>. For this mode, the
+ segments using <varname>restore_command</varname> or
+ <varname>restore_library</varname>. For this mode, the
parameters from this section and <xref
linkend="runtime-config-replication-standby"/> are of interest.
Parameters from <xref linkend="runtime-config-wal-recovery-target"/> will
@@ -3835,7 +3836,8 @@ include_dir 'conf.d'
<listitem>
<para>
The local shell command to execute to retrieve an archived segment of
- the WAL file series. This parameter is required for archive recovery,
+ the WAL file series. Either <varname>restore_command</varname> or
+ <xref linkend="guc-restore-library"/> is required for archive recovery,
but optional for streaming replication.
Any <literal>%f</literal> in the string is
replaced by the name of the file to retrieve from the archive,
@@ -3870,7 +3872,42 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows
<para>
This parameter can only be set in the <filename>postgresql.conf</filename>
- file or on the server command line.
+ file or on the server command line. It is only used if
+ <varname>restore_library</varname> is set to an empty string. If both
+ <varname>restore_command</varname> and
+ <varname>restore_library</varname> are set, an error will be raised.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry id="guc-restore-library" xreflabel="restore_library">
+ <term><varname>restore_library</varname> (<type>string</type>)
+ <indexterm>
+ <primary><varname>restore_library</varname> configuration parameter</primary>
+ </indexterm>
+ </term>
+ <listitem>
+ <para>
+ The library to use for recovery actions, including retrieving archived
+ segments of the WAL file series and executing tasks at restartpoints
+ and at recovery end. Either <xref linkend="guc-restore-command"/> or
+ <varname>restore_library</varname> is required for archive recovery,
+ but optional for streaming replication. If this parameter is set to an
+ empty string (the default), restoring via shell is enabled, and
+ <varname>restore_command</varname>,
+ <varname>archive_cleanup_command</varname> and
+ <varname>recovery_end_command</varname> are used. If both
+ <varname>restore_library</varname> and any of
+ <varname>restore_command</varname>,
+ <varname>archive_cleanup_command</varname> or
+ <varname>recovery_end_command</varname> are set, an error will be
+ raised. Otherwise, the specified shared library is used for recovery.
+ For more information, see <xref linkend="wal-modules"/>.
+ </para>
+
+ <para>
+ This parameter can only be set in the
+ <filename>postgresql.conf</filename> file or on the server command line.
</para>
</listitem>
</varlistentry>
@@ -3915,7 +3952,10 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows
</para>
<para>
This parameter can only be set in the <filename>postgresql.conf</filename>
- file or on the server command line.
+ file or on the server command line. It is only used if
+ <varname>restore_library</varname> is set to an empty string. If both
+ <varname>archive_cleanup_command</varname> and
+ <varname>restore_library</varname> are set, an error will be raised.
</para>
</listitem>
</varlistentry>
@@ -3944,7 +3984,10 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows
</para>
<para>
This parameter can only be set in the <filename>postgresql.conf</filename>
- file or on the server command line.
+ file or on the server command line. It is only used if
+ <varname>restore_library</varname> is set to an empty string. If both
+ <varname>recovery_end_command</varname> and
+ <varname>restore_library</varname> are set, an error will be raised.
</para>
</listitem>
</varlistentry>
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index f180607528..6266e2df7f 100644
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -627,7 +627,8 @@ protocol to make nodes agree on a serializable transactional order.
<para>
In standby mode, the server continuously applies WAL received from the
primary server. The standby server can read WAL from a WAL archive
- (see <xref linkend="guc-restore-command"/>) or directly from the primary
+ (see <xref linkend="guc-restore-command"/> and
+ <xref linkend="guc-restore-library"/>) or directly from the primary
over a TCP connection (streaming replication). The standby server will
also attempt to restore any WAL found in the standby cluster's
<filename>pg_wal</filename> directory. That typically happens after a server
@@ -638,9 +639,11 @@ protocol to make nodes agree on a serializable transactional order.
<para>
At startup, the standby begins by restoring all WAL available in the
- archive location, calling <varname>restore_command</varname>. Once it
- reaches the end of WAL available there and <varname>restore_command</varname>
- fails, it tries to restore any WAL available in the <filename>pg_wal</filename> directory.
+ archive location, either by calling <varname>restore_command</varname> or
+ by executing the <varname>restore_library</varname>'s restore callback.
+ Once it reaches the end of WAL available there and
+ <varname>restore_command</varname> or the restore callback fails, it tries
+ to restore any WAL available in the <filename>pg_wal</filename> directory.
If that fails, and streaming replication has been configured, the
standby tries to connect to the primary server and start streaming WAL
from the last valid record found in archive or <filename>pg_wal</filename>. If that fails
@@ -698,7 +701,8 @@ protocol to make nodes agree on a serializable transactional order.
server (see <xref linkend="backup-pitr-recovery"/>). Create a file
<link linkend="file-standby-signal"><filename>standby.signal</filename></link><indexterm><primary>standby.signal</primary></indexterm>
in the standby's cluster data
- directory. Set <xref linkend="guc-restore-command"/> to a simple command to copy files from
+ directory. Set <xref linkend="guc-restore-command"/> or
+ <xref linkend="guc-restore-library"/> to copy files from
the WAL archive. If you plan to have multiple standby servers for high
availability purposes, make sure that <varname>recovery_target_timeline</varname> is set to
<literal>latest</literal> (the default), to make the standby server follow the timeline change
@@ -707,7 +711,8 @@ protocol to make nodes agree on a serializable transactional order.
<note>
<para>
- <xref linkend="guc-restore-command"/> should return immediately
+ <xref linkend="guc-restore-command"/> and restore callbacks provided by
+ <xref linkend="guc-restore-library"/> should return immediately
if the file does not exist; the server will retry the command again if
necessary.
</para>
@@ -731,8 +736,10 @@ protocol to make nodes agree on a serializable transactional order.
<para>
If you're using a WAL archive, its size can be minimized using the <xref
- linkend="guc-archive-cleanup-command"/> parameter to remove files that are no
- longer required by the standby server.
+ linkend="guc-archive-cleanup-command"/> parameter or the
+ <xref linkend="guc-restore-library"/>'s
+ <function>archive_cleanup_cb</function> callback function to remove files
+ that are no longer required by the standby server.
The <application>pg_archivecleanup</application> utility is designed specifically to
be used with <varname>archive_cleanup_command</varname> in typical single-standby
configurations, see <xref linkend="pgarchivecleanup"/>.
diff --git a/doc/src/sgml/wal-modules.sgml b/doc/src/sgml/wal-modules.sgml
index 283bba782d..7607355696 100644
--- a/doc/src/sgml/wal-modules.sgml
+++ b/doc/src/sgml/wal-modules.sgml
@@ -11,6 +11,10 @@
to the manipulation of WAL segments by the backend.
</para>
+ <para>
+ A single module may be used for both archive and recovery modules.
+ </para>
+
<sect1 id="archive-modules">
<title>Archive Modules</title>
<indexterm zone="archive-modules">
@@ -48,7 +52,7 @@
</para>
<sect2 id="archive-module-init">
- <title>Initialization Functions</title>
+ <title>Archive Module Initialization Functions</title>
<indexterm zone="archive-module-init">
<primary>_PG_archive_module_init</primary>
</indexterm>
@@ -75,6 +79,12 @@ typedef void (*ArchiveModuleInit) (struct ArchiveModuleCallbacks *cb);
Only the <function>archive_file_cb</function> callback is required. The
others are optional.
</para>
+
+ <note>
+ <para>
+ <varname>archive_library</varname> is only loaded in the archiver process.
+ </para>
+ </note>
</sect2>
<sect2 id="archive-module-callbacks">
@@ -141,6 +151,165 @@ typedef bool (*ArchiveFileCB) (const char *file, const char *path);
<programlisting>
typedef void (*ArchiveShutdownCB) (void);
+</programlisting>
+ </para>
+ </sect3>
+ </sect2>
+ </sect1>
+
+ <sect1 id="recovery-modules">
+ <title>Recovery Modules</title>
+ <indexterm zone="recovery-modules">
+ <primary>Recovery Modules</primary>
+ </indexterm>
+
+ <para>
+ PostgreSQL provides infrastructure to create custom modules for
+ recovery (see <xref linkend="continuous-archiving"/>). While
+ a shell command like <xref linkend="guc-restore-command"/>) is
+ much simpler, a custom module will often be considerably more robust
+ and performant.
+ </para>
+
+ <para>
+ When a custom <xref linkend="guc-restore-library"/> is configured,
+ PostgreSQL will use the module for recovery actions. It is
+ ultimately up to the module to decide how to accomplish each task,
+ but some recommendations are listed at
+ <xref linkend="backup-pitr-recovery"/>.
+ </para>
+
+ <para>
+ Write-ahead log modules must at least consist of an initialization
+ function
+ (see <xref linkend="recovery-module-init"/>) and the required callbacks
+ (see <xref linkend="recovery-module-callbacks"/>). However, write-ahead
+ log modules are also permitted to do much more (e.g., declare GUCs and
+ register background workers).
+ </para>
+
+ <sect2 id="recovery-module-init">
+ <title>Recovery Module Initialization Functions</title>
+ <indexterm zone="recovery-module-init">
+ <primary>_PG_recovery_module_init</primary>
+ </indexterm>
+ <para>
+ A recovery library is loaded by dynamically loading a shared library with
+ the <xref linkend="guc-restore-library"/> as the library base name. The
+ normal library search path is used to locate the library. To provide the
+ required recovery module callbacks and to indicate that the library is
+ actually a recovery module, it needs to provide a function named
+ <function>_PG_recovery_module_init</function>. This function is passed a
+ struct that needs to be filled with the callback function pointers for
+ individual actions.
+
+<programlisting>
+typedef struct RecoveryModuleCallbacks
+{
+ RecoveryRestoreCB restore_cb;
+ RecoveryArchiveCleanupCB archive_cleanup_cb;
+ RecoveryEndCB recovery_end_cb;
+ RecoveryShutdownCB shutdown_cb;
+} RecoveryModuleCallbacks;
+typedef void (*RecoveryModuleInit) (struct RecoveryModuleCallbacks *cb);
+</programlisting>
+
+ The <function>restore_cb</function> callback is required for archive
+ recovery, but it is optional for streaming replication. The others are
+ always optional.
+ </para>
+
+ <note>
+ <para>
+ <varname>restore_library</varname> is only loaded in the startup and
+ checkpointer processes and in single-user mode.
+ </para>
+ </note>
+ </sect2>
+
+ <sect2 id="recovery-module-callbacks">
+ <title>Recovery Module Callbacks</title>
+ <para>
+ The recovery callbacks define the actual behavior of the module. The
+ server will call them as required to execute recovery actions.
+ </para>
+
+ <sect3 id="recovery-module-restore">
+ <title>Restore Callback</title>
+ <para>
+ The <function>restore_cb</function> callback is called to retrieve a
+ single archived segment of the WAL file series for archive recovery or
+ streaming replication.
+
+<programlisting>
+typedef bool (*RecoveryRestoreCB) (const char *file, const char *path, const char *lastRestartPointFileName);
+</programlisting>
+
+ This callback must return <literal>true</literal> only if the file was
+ successfully retrieved. If the file is not available in the archives, the
+ callback must return <literal>false</literal>.
+ <replaceable>file</replaceable> will contain just the file name
+ of the WAL file to retrieve, while <replaceable>path</replaceable>
+ contains the destination's relative path (including the file name).
+ <replaceable>lastRestartPointFileName</replaceable> will contain the name
+ of the file containing the last valid restart point. That is the earliest
+ file that must be kept to allow a restore to be restartable, so this
+ information can be used to truncate the archive to just the minimum
+ required to support restarting from the current restore.
+ <replaceable>lastRestartPointFileName</replaceable> is typically only used
+ by warm-standby configurations (see <xref linkend="warm-standby"/>). Note
+ that if multiple standby servers are restoring from the same archive
+ directory, you will need to ensure that you do not delete WAL files until
+ they are no longer needed by any of the servers.
+ </para>
+ </sect3>
+
+ <sect3 id="recovery-module-archive-cleanup">
+ <title>Archive Cleanup Callback</title>
+ <para>
+ The <function>archive_cleanup_cb</function> callback is called at every
+ restart point by the checkpointer process and is intended to provide a
+ mechanism for cleaning up old archived WAL files that are no longer
+ needed by the standby server.
+
+<programlisting>
+typedef void (*RecoveryArchiveCleanupCB) (const char *lastRestartPointFileName);
+</programlisting>
+
+ <replaceable>lastRestartPointFileName</replaceable> will contain the
+ name of the file that includes the last valid restart point, like in
+ <link linkend="recovery-module-restore"><function>restore_cb</function></link>.
+ </para>
+ </sect3>
+
+ <sect3 id="recovery-module-end">
+ <title>Recovery End Callback</title>
+ <para>
+ The <function>recovery_end_cb</function> callback is called once at the
+ end of recovery and is intended to provide a mechanism for cleanup
+ following the end of replication or recovery.
+
+<programlisting>
+typedef void (*RecoveryEndCB) (const char *lastRestartPointFileName);
+</programlisting>
+
+ <replaceable>lastRestartPointFileName</replaceable> will contain the name
+ of the file containing the last valid restart point, like in
+ <link linkend="recovery-module-restore"><function>restore_cb</function></link>.
+ </para>
+ </sect3>
+
+ <sect3 id="recovery-module-shutdown">
+ <title>Shutdown Callback</title>
+ <para>
+ The <function>shutdown_cb</function> callback is called when a process
+ that has loaded the recovery module exits (e.g., after an error) or the
+ value of <xref linkend="guc-restore-library"/> changes. If no
+ <function>shutdown_cb</function> is defined, no special action is taken in
+ these situations.
+
+<programlisting>
+typedef void (*RecoveryShutdownCB) (void);
</programlisting>
</para>
</sect3>
diff --git a/contrib/basic_wal_module/Makefile b/contrib/basic_wal_module/Makefile
index 1f88aaf469..b92126ff52 100644
--- a/contrib/basic_wal_module/Makefile
+++ b/contrib/basic_wal_module/Makefile
@@ -9,6 +9,8 @@ REGRESS_OPTS = --temp-config $(top_srcdir)/contrib/basic_wal_module/basic_wal_mo
# which typical installcheck users do not have (e.g. buildfarm clients).
NO_INSTALLCHECK = 1
+TAP_TESTS = 1
+
ifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
diff --git a/contrib/basic_wal_module/basic_wal_module.c b/contrib/basic_wal_module/basic_wal_module.c
index 78c36656a8..e17585cd93 100644
--- a/contrib/basic_wal_module/basic_wal_module.c
+++ b/contrib/basic_wal_module/basic_wal_module.c
@@ -17,6 +17,11 @@
* a file is successfully archived and then the system crashes before
* a durable record of the success has been made.
*
+ * This file also demonstrates a basic restore library implementation that
+ * is roughly equivalent to the following shell command:
+ *
+ * cp /path/to/archivedir/%f %p
+ *
* Copyright (c) 2022-2023, PostgreSQL Global Development Group
*
* IDENTIFICATION
@@ -30,6 +35,7 @@
#include <sys/time.h>
#include <unistd.h>
+#include "access/xlogarchive.h"
#include "common/int.h"
#include "miscadmin.h"
#include "postmaster/pgarch.h"
@@ -48,6 +54,8 @@ static bool basic_archive_file(const char *file, const char *path);
static void basic_archive_file_internal(const char *file, const char *path);
static bool check_archive_directory(char **newval, void **extra, GucSource source);
static bool compare_files(const char *file1, const char *file2);
+static bool basic_restore_file(const char *file, const char *path,
+ const char *lastRestartPointFileName);
/*
* _PG_init
@@ -58,7 +66,7 @@ void
_PG_init(void)
{
DefineCustomStringVariable("basic_wal_module.archive_directory",
- gettext_noop("Archive file destination directory."),
+ gettext_noop("Archive file source/destination directory."),
NULL,
&archive_directory,
"",
@@ -87,6 +95,19 @@ _PG_archive_module_init(ArchiveModuleCallbacks *cb)
cb->archive_file_cb = basic_archive_file;
}
+/*
+ * _PG_recovery_module_init
+ *
+ * Returns the module's restore callback.
+ */
+void
+_PG_recovery_module_init(RecoveryModuleCallbacks *cb)
+{
+ AssertVariableIsOfType(&_PG_recovery_module_init, RecoveryModuleInit);
+
+ cb->restore_cb = basic_restore_file;
+}
+
/*
* check_archive_directory
*
@@ -99,8 +120,8 @@ check_archive_directory(char **newval, void **extra, GucSource source)
/*
* The default value is an empty string, so we have to accept that value.
- * Our check_configured callback also checks for this and prevents
- * archiving from proceeding if it is still empty.
+ * Our check_configured and restore callbacks also check for this and
+ * prevent archiving or recovery from proceeding if it is still empty.
*/
if (*newval == NULL || *newval[0] == '\0')
return true;
@@ -368,3 +389,45 @@ compare_files(const char *file1, const char *file2)
return ret;
}
+
+/*
+ * basic_restore_file
+ *
+ * Retrieves one file from the WAL archives.
+ */
+static bool
+basic_restore_file(const char *file, const char *path,
+ const char *lastRestartPointFileName)
+{
+ char source[MAXPGPATH];
+ struct stat st;
+
+ ereport(DEBUG1,
+ (errmsg("restoring \"%s\" via basic_wal_module", file)));
+
+ if (archive_directory == NULL || archive_directory[0] == '\0')
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("\"basic_wal_module.archive_directory\" is not set")));
+
+ /*
+ * Check whether the file exists. If not, we return false to indicate that
+ * there are no more files to restore.
+ */
+ snprintf(source, MAXPGPATH, "%s/%s", archive_directory, file);
+ if (stat(source, &st) != 0)
+ {
+ int elevel = (errno == ENOENT) ? DEBUG1 : ERROR;
+
+ ereport(elevel,
+ (errcode_for_file_access(),
+ errmsg("could not stat file \"%s\": %m", source)));
+ return false;
+ }
+
+ copy_file(source, path);
+
+ ereport(DEBUG1,
+ (errmsg("restored \"%s\" via basic_wal_module", file)));
+ return true;
+}
diff --git a/contrib/basic_wal_module/meson.build b/contrib/basic_wal_module/meson.build
index 59939d71c4..fe68a806a9 100644
--- a/contrib/basic_wal_module/meson.build
+++ b/contrib/basic_wal_module/meson.build
@@ -31,4 +31,9 @@ tests += {
# which typical runningcheck users do not have (e.g. buildfarm clients).
'runningcheck': false,
},
+ 'tap': {
+ 'tests': [
+ 't/001_restore.pl',
+ ],
+ },
}
diff --git a/contrib/basic_wal_module/t/001_restore.pl b/contrib/basic_wal_module/t/001_restore.pl
new file mode 100644
index 0000000000..c9f39ea413
--- /dev/null
+++ b/contrib/basic_wal_module/t/001_restore.pl
@@ -0,0 +1,44 @@
+
+# Copyright (c) 2022, PostgreSQL Global Development Group
+
+use strict;
+use warnings;
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# start a node
+my $node = PostgreSQL::Test::Cluster->new('node');
+$node->init(has_archiving => 1, allows_streaming => 1);
+my $archive_dir = $node->archive_dir;
+$archive_dir =~ s!\\!/!g if $PostgreSQL::Test::Utils::windows_os;
+$node->append_conf('postgresql.conf', "archive_command = ''");
+$node->append_conf('postgresql.conf', "archive_library = 'basic_wal_module'");
+$node->append_conf('postgresql.conf', "basic_wal_module.archive_directory = '$archive_dir'");
+$node->start;
+
+# backup the node
+my $backup = 'backup';
+$node->backup($backup);
+
+# generate some new WAL files
+$node->safe_psql('postgres', "CREATE TABLE test (a INT);");
+$node->safe_psql('postgres', "SELECT pg_switch_wal();");
+$node->safe_psql('postgres', "INSERT INTO test VALUES (1);");
+
+# shut down the node (this should archive all WAL files)
+$node->stop;
+
+# restore from the backup
+my $restore = PostgreSQL::Test::Cluster->new('restore');
+$restore->init_from_backup($node, $backup, has_restoring => 1, standby => 0);
+$restore->append_conf('postgresql.conf', "restore_command = ''");
+$restore->append_conf('postgresql.conf', "restore_library = 'basic_wal_module'");
+$restore->append_conf('postgresql.conf', "basic_wal_module.archive_directory = '$archive_dir'");
+$restore->start;
+
+# ensure post-backup WAL was replayed
+my $result = $restore->safe_psql("postgres", "SELECT count(*) FROM test;");
+is($result, "1", "check restore content");
+
+done_testing();
--
2.39.0
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