Rework shutdown callback of archiver modules

As currently designed, with a callback registered in a ERROR_CLEANUP
block, the shutdown callback would get called twice when updating
archive_library on SIGHUP, which is something that we want to avoid to
ease the life of extension writers.

Anyway, an ERROR in the archiver process is treated as a FATAL, stopping
it immediately, hence there is no need for a ERROR_CLEANUP block.
Instead of that, the shutdown callback is not called upon
before_shmem_exit(), giving to the modules the opportunity to do any
cleanup actions before the server shuts down its subsystems.

While on it, this commit adds some testing coverage for the shutdown
callback.  Neither shell_archive nor basic_archive have been using it,
and one is added to shell_archive, whose trigger is checked in a TAP
test through a shutdown sequence.

Author: Nathan Bossart, Bharath Rupireddy
Reviewed-by: Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/20221015221328.GB1821022@nathanxps13
Backpatch-through: 15

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 66312b53b810ae2a126da7b2f65686a954c65c79..6c649336e160e3b8ec9fb53a1f22a4bc56b635f4 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3625,8 +3625,9 @@ include_dir 'conf.d'
         The library to use for archiving completed WAL file segments.  If set to
         an empty string (the default), archiving via shell is enabled, and
         <xref linkend="guc-archive-command"/> is used.  Otherwise, the specified
-        shared library is used for archiving.  For more information, see
-        <xref linkend="backup-archiving-wal"/> and
+        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"/>.
        </para>
        <para>

diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index 3868cd7bd353acdd649804a0135dbdf8ed19bf04..2670e41666ac687a4ca5a8afd01f5137a1e1a6ab 100644 (file)
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -144,7 +144,7 @@ static void pgarch_die(int code, Datum arg);
 static void HandlePgArchInterrupts(void);
 static int ready_file_comparator(Datum a, Datum b, void *arg);
 static void LoadArchiveLibrary(void);
-static void call_archive_module_shutdown_callback(int code, Datum arg);
+static void pgarch_call_module_shutdown_cb(int code, Datum arg);
 
 /* Report shared memory space needed by PgArchShmemInit */
 Size
@@ -252,13 +252,7 @@ PgArchiverMain(void)
    /* Load the archive_library. */
    LoadArchiveLibrary();
 
-   PG_ENSURE_ERROR_CLEANUP(call_archive_module_shutdown_callback, 0);
-   {
-       pgarch_MainLoop();
-   }
-   PG_END_ENSURE_ERROR_CLEANUP(call_archive_module_shutdown_callback, 0);
-
-   call_archive_module_shutdown_callback(0, 0);
+   pgarch_MainLoop();
 
    proc_exit(0);
 }
@@ -803,19 +797,14 @@ HandlePgArchInterrupts(void)
 
        if (archiveLibChanged)
        {
-           /*
-            * Call the currently loaded archive module's shutdown callback,
-            * if one is defined.
-            */
-           call_archive_module_shutdown_callback(0, 0);
-
            /*
             * Ideally, we would simply unload the previous archive module and
             * load the new one, but there is presently no mechanism for
             * unloading a library (see the comment above
             * internal_load_library()).  To deal with this, we simply restart
             * the archiver.  The new archive module will be loaded when the
-            * new archiver process starts up.
+            * new archiver process starts up.  Note that this triggers the
+            * module's shutdown callback, if defined.
             */
            ereport(LOG,
                    (errmsg("restarting archiver process because value of "
@@ -858,15 +847,15 @@ LoadArchiveLibrary(void)
    if (ArchiveContext.archive_file_cb == NULL)
        ereport(ERROR,
                (errmsg("archive modules must register an archive callback")));
+
+   before_shmem_exit(pgarch_call_module_shutdown_cb, 0);
 }
 
 /*
- * call_archive_module_shutdown_callback
- *
- * Calls the loaded archive module's shutdown callback, if one is defined.
+ * Call the shutdown callback of the loaded archive module, if defined.
  */
 static void
-call_archive_module_shutdown_callback(int code, Datum arg)
+pgarch_call_module_shutdown_cb(int code, Datum arg)
 {
    if (ArchiveContext.shutdown_cb != NULL)
        ArchiveContext.shutdown_cb();

diff --git a/src/backend/postmaster/shell_archive.c b/src/backend/postmaster/shell_archive.c
index 8a54d02e7bbd82eaed949518c562623ae40814ef..71d567065a205d9bc98fd7bfcebdd34845bc2c98 100644 (file)
--- a/src/backend/postmaster/shell_archive.c
+++ b/src/backend/postmaster/shell_archive.c
@@ -23,6 +23,7 @@
 
 static bool shell_archive_configured(void);
 static bool shell_archive_file(const char *file, const char *path);
+static void shell_archive_shutdown(void);
 
 void
 shell_archive_init(ArchiveModuleCallbacks *cb)
@@ -31,6 +32,7 @@ shell_archive_init(ArchiveModuleCallbacks *cb)
 
    cb->check_configured_cb = shell_archive_configured;
    cb->archive_file_cb = shell_archive_file;
+   cb->shutdown_cb = shell_archive_shutdown;
 }
 
 static bool
@@ -156,3 +158,9 @@ shell_archive_file(const char *file, const char *path)
    elog(DEBUG1, "archived write-ahead log file \"%s\"", file);
    return true;
 }
+
+static void
+shell_archive_shutdown(void)
+{
+   elog(DEBUG1, "archiver process shutting down");
+}

diff --git a/src/test/recovery/t/020_archive_status.pl b/src/test/recovery/t/020_archive_status.pl
index 550fb37cb68993c3c1f1465593c7ce2049b3db85..2108d50073abf6291033187448997ccd64e1b75f 100644 (file)
--- a/src/test/recovery/t/020_archive_status.pl
+++ b/src/test/recovery/t/020_archive_status.pl
@@ -234,4 +234,18 @@ ok( -f "$standby2_data/$segment_path_1_done"
    ".done files created after archive success with archive_mode=always on standby"
 );
 
+# Check that the archiver process calls the shell archive module's shutdown
+# callback.
+$standby2->append_conf('postgresql.conf', "log_min_messages = debug1");
+$standby2->reload;
+
+# Run a query to make sure that the reload has taken effect.
+$standby2->safe_psql('postgres', q{SELECT 1});
+my $log_location = -s $standby2->logfile;
+
+$standby2->stop;
+my $logfile = slurp_file($standby2->logfile, $log_location);
+ok( $logfile =~ qr/archiver process shutting down/,
+   'check shutdown callback of shell archive module');
+
 done_testing();