On Wed, Nov 22, 2023 at 09:23:21PM +0530, Ashutosh Bapat wrote:
> On Tue, Nov 21, 2023 at 6:56 AM Michael Paquier <mich...@paquier.xyz> wrote:
>> I've never seen in recent years a need for a given test to use more
>> than 4~5 points.  But I guess that you've seen more than that wanted
>> in a prod environment with a fork of Postgres?
> 
> A given case may not require more than 4 -5 points but users may
> create scripts with many frequently required injection points and
> install handlers for them.

Sure, if a callback is generic enough it could be shared across
multiple points.

> The injection_run function is called from the place where the
> injection point is declared but that place does not know what
> injection function is going to be run. So a user can not pass
> arguments to injection declaration.

It is possible to make that predictible but it means that a callback
is most likely to be used by one single point.  This makes extensions
in charge of holding the callbacks more complicated, at the benefit of
keeping a minimal footprint in the backend code.

> What injection to run is decided
> by the injection_attach and thus one can pass arguments to it but then
> injection_attach stores the information in the shared memory from
> where it's picked up by injection_run. So even though you don't want
> to store the arguments in the shared memory, you are creating a design
> which takes us towards that direction eventually - otherwise users
> will end up writing many injection functions - one for each possible
> combination of count, sleep, conditional variable etc. But let's see
> whether that happens to be the case in practice. We will need to
> evolve this feature based on usage.

A one-one mapping between callback and point is not always necessary.
If you wish to use a combination of N points with a sleep callback and
different sleep times, one can just register a second shmem area in
the extension holding the callbacks that links the point names with
the sleep time to use.

> shmem hash size won't depend upon the number of functions we write in
> the core. Yes it will add to the core code and may add maintenance
> burden. So I understand your inclination to keep the core minimal.

Yeah, without a clear benefit, my point is just to throw the
responsibility to extension developers for now, which would mean the
addition of tests that depend on test_injection_points/, or just
install this extension optionally in other code path that need it.
Maybe 0004 should be in src/test/recovery/ and do that, actually..
I'll most likely agree with extending all the backend stuff in a more
meaningful way, but I am not sure which method should be enforced.

> If the session which attaches to an injection point is same as the
> session where the injection point is triggered (most of the ERROR and
> NOTICE injections will see this pattern), we don't need shared memory.
> There's a performance penalty to it since injection_run will look up
> shared memory. For WAIT we may or may not need shared memory. But
> let's see what other think and what usage patterns we see.

The first POC of the patch that you can find at the top of this thread
did that, actually, but this is too limited.  IMO, linking things to a
central table is just *much* more useful.

I've implemented a v5 that switches the cache to use a seconf hash
table on TopMemoryContext for the cache instead of an array.  This
makes the cache handling slightly cleaner, so your suggestion was
right.  0003 and 0004 are the same as previously, passing or failing
under the same conditions.  I'm wondering if folks have other comments
about 0001 and 0002?  It sounds to me like the consensus is that this
stuff is useful and that there are no string objections, so feel free
to comment.

I don't want to propose 0003 in the tree, just an improved version of
0004 for the test coverage (still need to improve that).
--
Michael
From 702f5fa5a9ccede4c2c4e6c056f567b77332702d Mon Sep 17 00:00:00 2001
From: Michael Paquier <mich...@paquier.xyz>
Date: Fri, 24 Nov 2023 10:35:26 +0900
Subject: [PATCH v5 1/4] Add backend facility for injection points

This adds a set of routines allowing developers to attach, detach and
run custom code based on arbitrary code paths set with a centralized
macro called INJECTION_POINT().  Injection points are registered in a
shared hash table.  Processes also use a local cache to over loading
callbacks more than necessary, cleaning up their cache if a callback has
found to be removed.
---
 src/include/pg_config.h.in                    |   3 +
 src/include/utils/injection_point.h           |  36 ++
 src/backend/storage/ipc/ipci.c                |   3 +
 src/backend/storage/lmgr/lwlocknames.txt      |   1 +
 .../utils/activity/wait_event_names.txt       |   1 +
 src/backend/utils/misc/Makefile               |   1 +
 src/backend/utils/misc/injection_point.c      | 317 ++++++++++++++++++
 src/backend/utils/misc/meson.build            |   1 +
 doc/src/sgml/installation.sgml                |  30 ++
 doc/src/sgml/xfunc.sgml                       |  56 ++++
 configure                                     |  34 ++
 configure.ac                                  |   7 +
 meson.build                                   |   1 +
 meson_options.txt                             |   3 +
 src/Makefile.global.in                        |   1 +
 src/tools/pgindent/typedefs.list              |   2 +
 16 files changed, 497 insertions(+)
 create mode 100644 src/include/utils/injection_point.h
 create mode 100644 src/backend/utils/misc/injection_point.c

diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index d8a2985567..7a976821e5 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -701,6 +701,9 @@
 /* Define to build with ICU support. (--with-icu) */
 #undef USE_ICU
 
+/* Define to 1 to build with injection points. (--enable-injection-points) */
+#undef USE_INJECTION_POINTS
+
 /* Define to 1 to build with LDAP support. (--with-ldap) */
 #undef USE_LDAP
 
diff --git a/src/include/utils/injection_point.h b/src/include/utils/injection_point.h
new file mode 100644
index 0000000000..6335260fea
--- /dev/null
+++ b/src/include/utils/injection_point.h
@@ -0,0 +1,36 @@
+/*-------------------------------------------------------------------------
+ * injection_point.h
+ *	  Definitions related to injection points.
+ *
+ * Copyright (c) 2001-2023, PostgreSQL Global Development Group
+ *
+ * src/include/utils/injection_point.h
+ * ----------
+ */
+#ifndef INJECTION_POINT_H
+#define INJECTION_POINT_H
+
+/*
+ * Injections points require --enable-injection-points.
+ */
+#ifdef USE_INJECTION_POINTS
+#define INJECTION_POINT(name) InjectionPointRun(name)
+#else
+#define INJECTION_POINT(name) ((void) name)
+#endif
+
+/*
+ * Typedef for callback function launched by an injection point.
+ */
+typedef void (*InjectionPointCallback) (const char *name);
+
+extern Size InjectionPointShmemSize(void);
+extern void InjectionPointShmemInit(void);
+
+extern void InjectionPointAttach(const char *name,
+								 const char *library,
+								 const char *function);
+extern void InjectionPointRun(const char *name);
+extern void InjectionPointDetach(const char *name);
+
+#endif							/* INJECTION_POINT_H */
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index a3d8eacb8d..12b8a42fd9 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -48,6 +48,7 @@
 #include "storage/sinvaladt.h"
 #include "storage/spin.h"
 #include "utils/guc.h"
+#include "utils/injection_point.h"
 #include "utils/snapmgr.h"
 #include "utils/wait_event.h"
 
@@ -143,6 +144,7 @@ CalculateShmemSize(int *num_semaphores)
 	size = add_size(size, AsyncShmemSize());
 	size = add_size(size, StatsShmemSize());
 	size = add_size(size, WaitEventExtensionShmemSize());
+	size = add_size(size, InjectionPointShmemSize());
 #ifdef EXEC_BACKEND
 	size = add_size(size, ShmemBackendArraySize());
 #endif
@@ -302,6 +304,7 @@ CreateSharedMemoryAndSemaphores(void)
 	AsyncShmemInit();
 	StatsShmemInit();
 	WaitEventExtensionShmemInit();
+	InjectionPointShmemInit();
 
 #ifdef EXEC_BACKEND
 
diff --git a/src/backend/storage/lmgr/lwlocknames.txt b/src/backend/storage/lmgr/lwlocknames.txt
index f72f2906ce..42a048746d 100644
--- a/src/backend/storage/lmgr/lwlocknames.txt
+++ b/src/backend/storage/lmgr/lwlocknames.txt
@@ -54,3 +54,4 @@ XactTruncationLock					44
 WrapLimitsVacuumLock				46
 NotifyQueueTailLock					47
 WaitEventExtensionLock				48
+InjectionPointLock				49
diff --git a/src/backend/utils/activity/wait_event_names.txt b/src/backend/utils/activity/wait_event_names.txt
index d7995931bd..5631d29138 100644
--- a/src/backend/utils/activity/wait_event_names.txt
+++ b/src/backend/utils/activity/wait_event_names.txt
@@ -319,6 +319,7 @@ XactTruncation	"Waiting to execute <function>pg_xact_status</function> or update
 WrapLimitsVacuum	"Waiting to update limits on transaction id and multixact consumption."
 NotifyQueueTail	"Waiting to update limit on <command>NOTIFY</command> message storage."
 WaitEventExtension	"Waiting to read or update custom wait events information for extensions."
+InjectionPoint	"Waiting to read or update information related to injection points."
 
 XactBuffer	"Waiting for I/O on a transaction status SLRU buffer."
 CommitTsBuffer	"Waiting for I/O on a commit timestamp SLRU buffer."
diff --git a/src/backend/utils/misc/Makefile b/src/backend/utils/misc/Makefile
index c2971c7678..d9f59785b9 100644
--- a/src/backend/utils/misc/Makefile
+++ b/src/backend/utils/misc/Makefile
@@ -21,6 +21,7 @@ OBJS = \
 	guc_funcs.o \
 	guc_tables.o \
 	help_config.o \
+	injection_point.o \
 	pg_config.o \
 	pg_controldata.o \
 	pg_rusage.o \
diff --git a/src/backend/utils/misc/injection_point.c b/src/backend/utils/misc/injection_point.c
new file mode 100644
index 0000000000..6bc349e7c7
--- /dev/null
+++ b/src/backend/utils/misc/injection_point.c
@@ -0,0 +1,317 @@
+/*-------------------------------------------------------------------------
+ *
+ * injection_point.c
+ *	  Routines to control and run injection points in the code.
+ *
+ * Injection points can be used to call arbitrary callbacks in specific
+ * places of the code, registering callbacks that would be run in the code
+ * paths where a named injection point exists.
+ *
+ * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/misc/injection_point.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <sys/stat.h>
+
+#include "fmgr.h"
+#include "miscadmin.h"
+#include "port/pg_bitutils.h"
+#include "storage/lwlock.h"
+#include "storage/shmem.h"
+#include "utils/hsearch.h"
+#include "utils/injection_point.h"
+#include "utils/memutils.h"
+
+#ifdef USE_INJECTION_POINTS
+
+/*
+ * Hash table for storing injection points.
+ *
+ * InjectionPointHash is used to find an injection point by name.
+ */
+static HTAB *InjectionPointHash;	/* find points from names */
+
+/* Field sizes */
+#define INJ_NAME_MAXLEN		64
+#define INJ_LIB_MAXLEN		128
+#define INJ_FUNC_MAXLEN		128
+
+typedef struct InjectionPointEntry
+{
+	char		name[INJ_NAME_MAXLEN];	/* hash key */
+	char		library[INJ_LIB_MAXLEN];	/* library */
+	char		function[INJ_FUNC_MAXLEN];	/* function */
+} InjectionPointEntry;
+
+#define INJECTION_POINT_HASH_INIT_SIZE	16
+#define INJECTION_POINT_HASH_MAX_SIZE	128
+
+/*
+ * Local cache of injection callbacks already loaded, stored in
+ * TopMemoryContext.
+ */
+typedef struct InjectionPointArrayEntry
+{
+	char		name[INJ_NAME_MAXLEN];
+	InjectionPointCallback callback;
+} InjectionPointCacheEntry;
+
+static HTAB *InjectionPointCache = NULL;
+
+/* utilities to handle the local array cache */
+static void
+injection_point_cache_add(const char *name,
+						  InjectionPointCallback callback)
+{
+	InjectionPointCacheEntry *entry;
+	bool		found;
+
+	/* If first time, initialize */
+	if (InjectionPointCache == NULL)
+	{
+		HASHCTL		hash_ctl;
+
+		hash_ctl.keysize = sizeof(char[INJ_NAME_MAXLEN]);
+		hash_ctl.entrysize = sizeof(InjectionPointCacheEntry);
+		hash_ctl.hcxt = TopMemoryContext;
+
+		InjectionPointCache = hash_create("InjectionPoint cache hash",
+										  INJECTION_POINT_HASH_MAX_SIZE,
+										  &hash_ctl,
+										  HASH_ELEM | HASH_STRINGS | HASH_CONTEXT);
+	}
+
+	entry = (InjectionPointCacheEntry *)
+		hash_search(InjectionPointCache, name, HASH_ENTER, &found);
+
+	if (!found)
+	{
+		memcpy(entry->name, name, strlen(name));
+		entry->callback = callback;
+	}
+}
+
+/*
+ * Remove entry from the local cache.  Note that this leaks a callback
+ * loaded but removed later on, which should have no consequence from
+ * a testing perspective.
+ */
+static void
+injection_point_cache_remove(const char *name)
+{
+	/* Leave if no cache */
+	if (InjectionPointCache == NULL)
+		return;
+
+	(void) hash_search(InjectionPointCache, name, HASH_REMOVE, NULL);
+}
+
+static InjectionPointCallback
+injection_point_cache_get(const char *name)
+{
+	bool		found;
+	InjectionPointCacheEntry *entry;
+
+	/* no callback if no cache yet */
+	if (InjectionPointCache == NULL)
+		return NULL;
+
+	entry = (InjectionPointCacheEntry *)
+		hash_search(InjectionPointCache, name, HASH_FIND, &found);
+
+	if (found)
+		return entry->callback;
+
+	return NULL;
+}
+#endif							/* USE_INJECTION_POINTS */
+
+/*
+ * Return the space for dynamic shared hash table.
+ */
+Size
+InjectionPointShmemSize(void)
+{
+#ifdef USE_INJECTION_POINTS
+	Size		sz = 0;
+
+	sz = add_size(sz, hash_estimate_size(INJECTION_POINT_HASH_MAX_SIZE,
+										 sizeof(InjectionPointEntry)));
+	return sz;
+#else
+	return 0;
+#endif
+}
+
+/*
+ * Allocate shmem space for dynamic shared hash.
+ */
+void
+InjectionPointShmemInit(void)
+{
+#ifdef USE_INJECTION_POINTS
+	HASHCTL		info;
+
+	/* key is a NULL-terminated string */
+	info.keysize = sizeof(char[INJ_NAME_MAXLEN]);
+	info.entrysize = sizeof(InjectionPointEntry);
+	InjectionPointHash = ShmemInitHash("InjectionPoint hash",
+									   INJECTION_POINT_HASH_INIT_SIZE,
+									   INJECTION_POINT_HASH_MAX_SIZE,
+									   &info,
+									   HASH_ELEM | HASH_STRINGS);
+#endif
+}
+
+#ifdef USE_INJECTION_POINTS
+static bool
+file_exists(const char *name)
+{
+	struct stat st;
+
+	Assert(name != NULL);
+	if (stat(name, &st) == 0)
+		return !S_ISDIR(st.st_mode);
+	else if (!(errno == ENOENT || errno == ENOTDIR))
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not access file \"%s\": %m", name)));
+	return false;
+}
+#endif
+
+/*
+ * Attach a new injection point.
+ */
+void
+InjectionPointAttach(const char *name,
+					 const char *library,
+					 const char *function)
+{
+#ifdef USE_INJECTION_POINTS
+	InjectionPointEntry *entry_by_name;
+	bool		found;
+
+	if (strlen(name) >= INJ_NAME_MAXLEN)
+		elog(ERROR, "injection point name %s too long", name);
+	if (strlen(library) >= INJ_LIB_MAXLEN)
+		elog(ERROR, "injection point library %s too long", library);
+	if (strlen(function) >= INJ_FUNC_MAXLEN)
+		elog(ERROR, "injection point function %s too long", function);
+
+	/*
+	 * Allocate and register a new injection point.  A new point should not
+	 * exist.  For testing purposes this should be fine.
+	 */
+	LWLockAcquire(InjectionPointLock, LW_EXCLUSIVE);
+	entry_by_name = (InjectionPointEntry *)
+		hash_search(InjectionPointHash, name,
+					HASH_ENTER, &found);
+	if (found)
+	{
+		LWLockRelease(InjectionPointLock);
+		elog(ERROR, "injection point \"%s\" already defined", name);
+	}
+
+	/* Save the entry */
+	memcpy(entry_by_name->name, name, sizeof(entry_by_name->name));
+	entry_by_name->name[INJ_NAME_MAXLEN - 1] = '\0';
+	memcpy(entry_by_name->library, library, sizeof(entry_by_name->library));
+	entry_by_name->library[INJ_LIB_MAXLEN - 1] = '\0';
+	memcpy(entry_by_name->function, function, sizeof(entry_by_name->function));
+	entry_by_name->function[INJ_FUNC_MAXLEN - 1] = '\0';
+
+	LWLockRelease(InjectionPointLock);
+
+#else
+	elog(ERROR, "Injection points are not supported by this build");
+#endif
+}
+
+/*
+ * Detach an existing injection point.
+ */
+void
+InjectionPointDetach(const char *name)
+{
+#ifdef USE_INJECTION_POINTS
+	bool		found;
+
+	LWLockAcquire(InjectionPointLock, LW_EXCLUSIVE);
+	hash_search(InjectionPointHash, name, HASH_REMOVE, &found);
+	LWLockRelease(InjectionPointLock);
+
+	if (!found)
+		elog(ERROR, "injection point \"%s\" not found", name);
+
+#else
+	elog(ERROR, "Injection points are not supported by this build");
+#endif
+}
+
+/*
+ * Execute an injection point, if defined.
+ *
+ * Check first the shared hash table, and adapt the local cache
+ * depending on that as it could be possible that an entry to run
+ * has been removed.
+ */
+void
+InjectionPointRun(const char *name)
+{
+#ifdef USE_INJECTION_POINTS
+	InjectionPointEntry *entry_by_name;
+	bool		found;
+	InjectionPointCallback injection_callback;
+
+	LWLockAcquire(InjectionPointLock, LW_SHARED);
+	entry_by_name = (InjectionPointEntry *)
+		hash_search(InjectionPointHash, name,
+					HASH_FIND, &found);
+	LWLockRelease(InjectionPointLock);
+
+	/*
+	 * If not found, do nothing and remove it from the local cache if it
+	 * existed there.
+	 */
+	if (!found)
+	{
+		injection_point_cache_remove(name);
+		return;
+	}
+
+	/*
+	 * Check if the callback exists in the local cache, to avoid unnecessary
+	 * external loads.
+	 */
+	injection_callback = injection_point_cache_get(name);
+	if (injection_callback == NULL)
+	{
+		char		path[MAXPGPATH];
+
+		/* Found, so just run the callback registered */
+		snprintf(path, MAXPGPATH, "%s/%s%s", pkglib_path,
+				 entry_by_name->library, DLSUFFIX);
+
+		if (!file_exists(path))
+			elog(ERROR, "could not find injection library \"%s\"", path);
+
+		injection_callback = (InjectionPointCallback)
+			load_external_function(path, entry_by_name->function, true, NULL);
+
+		/* add it to the local cache when found */
+		injection_point_cache_add(name, injection_callback);
+	}
+
+	injection_callback(name);
+#else
+	elog(ERROR, "Injection points are not supported by this build");
+#endif
+}
diff --git a/src/backend/utils/misc/meson.build b/src/backend/utils/misc/meson.build
index f719c97c05..1438859b69 100644
--- a/src/backend/utils/misc/meson.build
+++ b/src/backend/utils/misc/meson.build
@@ -6,6 +6,7 @@ backend_sources += files(
   'guc_funcs.c',
   'guc_tables.c',
   'help_config.c',
+  'injection_point.c',
   'pg_config.c',
   'pg_controldata.c',
   'pg_rusage.c',
diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
index b23b35cd8e..d5a2fcb084 100644
--- a/doc/src/sgml/installation.sgml
+++ b/doc/src/sgml/installation.sgml
@@ -1676,6 +1676,21 @@ build-postgresql:
        </listitem>
       </varlistentry>
 
+      <varlistentry id="configure-option-enable-injection-points">
+       <term><option>--enable-injection-points</option></term>
+       <listitem>
+        <para>
+        Compiles <productname>PostgreSQL</productname> with support for
+        injection points in the server.  This is valuable to inject
+        user-defined code to force specific conditions to happen on the
+        server in pre-defined code paths.  This option is disabled by default.
+        See <xref linkend="xfunc-addin-injection-points"/> for more details.
+        This option is only for developers to test specific concurrency
+        scenarios.
+        </para>
+       </listitem>
+      </varlistentry>
+
       <varlistentry id="configure-option-with-segsize-blocks">
        <term><option>--with-segsize-blocks=SEGSIZE_BLOCKS</option></term>
        <listitem>
@@ -3184,6 +3199,21 @@ ninja install
       </listitem>
      </varlistentry>
 
+     <varlistentry id="configure-injection-points-meson">
+      <term><option>-Dinjection_points={ true | false }</option></term>
+      <listitem>
+       <para>
+        Compiles <productname>PostgreSQL</productname> with support for
+        injection points in the server.  This is valuable to inject
+        user-defined code to force specific conditions to happen on the
+        server in pre-defined code paths.  This option is disabled by default.
+        See <xref linkend="xfunc-addin-injection-points"/> for more details.
+        This option is only for developers to test specific concurrency
+        scenarios.
+       </para>
+      </listitem>
+     </varlistentry>
+
       <varlistentry id="configure-segsize-blocks-meson">
        <term><option>-Dsegsize_blocks=SEGSIZE_BLOCKS</option></term>
        <listitem>
diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index 89116ae74c..66cc94b03b 100644
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -3510,6 +3510,62 @@ uint32 WaitEventExtensionNew(const char *wait_event_name)
     </para>
    </sect2>
 
+   <sect2 id="xfunc-addin-injection-points">
+    <title>Injection Points</title>
+
+    <para>
+     Add-ins can define injection points, that can register callbacks
+     to run user-defined code when going through a specific code path,
+     by calling:
+<programlisting>
+extern void InjectionPointAttach(const char *name,
+                                 const char *library,
+                                 const char *function);
+</programlisting>
+
+     <literal>name</literal> is the name of the injection point, that
+     will execute the <literal>function</literal> loaded from
+     <literal>library</library>.
+     Injection points are saved in a hash table in shared memory, and
+     last until the server is shut down.
+    </para>
+
+    <para>
+     Here is an example of callback for
+     <literal>InjectionPointCallback</literal>:
+<programlisting>
+static void
+custom_injection_callback(const char *name)
+{
+    elog(NOTICE, "%s: executed custom callback", name);
+}
+</programlisting>
+    </para>
+
+    <para>
+     Once an injection point is defined, running it requires to use
+     the following macro to trigger the callback given in a wanted code
+     path:
+<programlisting>
+INJECTION_POINT(name);
+</programlisting>
+    </para>
+
+    <para>
+     Optionally, it is possible to detach injection points by calling:
+<programlisting>
+extern void InjectionPointDetach(const char *name);
+</programlisting>
+    </para>
+
+    <para>
+     Enabling injections points requires
+     <option>--enable-injection-points</option> from
+     <command>configure</command> or <option>-Dinjection_points=true</option>
+     from <application>Meson</application>.
+    </para>
+   </sect2>
+
    <sect2 id="extend-cpp">
     <title>Using C++ for Extensibility</title>
 
diff --git a/configure b/configure
index c064115038..ce0ef0133d 100755
--- a/configure
+++ b/configure
@@ -759,6 +759,7 @@ CPPFLAGS
 LDFLAGS
 CFLAGS
 CC
+enable_injection_points
 enable_tap_tests
 enable_dtrace
 DTRACEFLAGS
@@ -839,6 +840,7 @@ enable_profiling
 enable_coverage
 enable_dtrace
 enable_tap_tests
+enable_injection_points
 with_blocksize
 with_segsize
 with_segsize_blocks
@@ -1532,6 +1534,8 @@ Optional Features:
   --enable-coverage       build with coverage testing instrumentation
   --enable-dtrace         build with DTrace support
   --enable-tap-tests      enable TAP tests (requires Perl and IPC::Run)
+  --enable-injection-points
+                          enable injection points (for testing)
   --enable-depend         turn on automatic dependency tracking
   --enable-cassert        enable assertion checks (for debugging)
   --disable-largefile     omit support for large files
@@ -3682,6 +3686,36 @@ fi
 
 
 
+#
+# Injection points
+#
+
+
+# Check whether --enable-injection-points was given.
+if test "${enable_injection_points+set}" = set; then :
+  enableval=$enable_injection_points;
+  case $enableval in
+    yes)
+
+$as_echo "#define USE_INJECTION_POINTS 1" >>confdefs.h
+
+      ;;
+    no)
+      :
+      ;;
+    *)
+      as_fn_error $? "no argument expected for --enable-injection-points option" "$LINENO" 5
+      ;;
+  esac
+
+else
+  enable_injection_points=no
+
+fi
+
+
+
+
 #
 # Block size
 #
diff --git a/configure.ac b/configure.ac
index f220b379b3..af13b6da69 100644
--- a/configure.ac
+++ b/configure.ac
@@ -250,6 +250,13 @@ PGAC_ARG_BOOL(enable, tap-tests, no,
               [enable TAP tests (requires Perl and IPC::Run)])
 AC_SUBST(enable_tap_tests)
 
+#
+# Injection points
+#
+PGAC_ARG_BOOL(enable, injection-points, no, [enable injection points (for testing)],
+              [AC_DEFINE([USE_INJECTION_POINTS], 1, [Define to 1 to build with injection points. (--enable-injection-points)])])
+AC_SUBST(enable_injection_points)
+
 #
 # Block size
 #
diff --git a/meson.build b/meson.build
index ee58ee7a06..151bc209a6 100644
--- a/meson.build
+++ b/meson.build
@@ -431,6 +431,7 @@ meson_bin = find_program(meson_binpath, native: true)
 ###############################################################
 
 cdata.set('USE_ASSERT_CHECKING', get_option('cassert') ? 1 : false)
+cdata.set('USE_INJECTION_POINTS', get_option('injection_points') ? 1 : false)
 
 blocksize = get_option('blocksize').to_int() * 1024
 
diff --git a/meson_options.txt b/meson_options.txt
index be1b327f54..7a5102df1a 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -43,6 +43,9 @@ option('cassert', type: 'boolean', value: false,
 option('tap_tests', type: 'feature', value: 'auto',
   description: 'Enable TAP tests')
 
+option('injection_points', type: 'boolean', value: false,
+  description: 'Enable injection points')
+
 option('PG_TEST_EXTRA', type: 'string', value: '',
   description: 'Enable selected extra tests')
 
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index b3ca6392a6..ceb5895d1b 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -203,6 +203,7 @@ enable_nls	= @enable_nls@
 enable_debug	= @enable_debug@
 enable_dtrace	= @enable_dtrace@
 enable_coverage	= @enable_coverage@
+enable_injection_points = @enable_injection_points@
 enable_tap_tests	= @enable_tap_tests@
 
 python_includespec	= @python_includespec@
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index dba3498a13..45d6c0c204 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1137,6 +1137,8 @@ IdentLine
 IdentifierLookup
 IdentifySystemCmd
 IfStackElem
+InjectionPointCacheEntry
+InjectionPointEntry
 ImportForeignSchemaStmt
 ImportForeignSchemaType
 ImportForeignSchema_function
-- 
2.42.0

From a83d06f7e67632b16178f103cbcee4216ac792bb Mon Sep 17 00:00:00 2001
From: Michael Paquier <mich...@paquier.xyz>
Date: Thu, 16 Nov 2023 14:00:48 +0900
Subject: [PATCH v5 2/4] Add test module test_injection_points

This is a test facility aimed at providing basic coverage for the code
routines of injection points.  This will be extended with more tests.
---
 src/test/modules/Makefile                     |   7 ++
 src/test/modules/meson.build                  |   1 +
 .../modules/test_injection_points/.gitignore  |   4 +
 .../modules/test_injection_points/Makefile    |  22 ++++
 .../expected/test_injection_points.out        | 117 ++++++++++++++++++
 .../modules/test_injection_points/meson.build |  37 ++++++
 .../sql/test_injection_points.sql             |  33 +++++
 .../test_injection_points--1.0.sql            |  36 ++++++
 .../test_injection_points.c                   |  91 ++++++++++++++
 .../test_injection_points.control             |   4 +
 10 files changed, 352 insertions(+)
 create mode 100644 src/test/modules/test_injection_points/.gitignore
 create mode 100644 src/test/modules/test_injection_points/Makefile
 create mode 100644 src/test/modules/test_injection_points/expected/test_injection_points.out
 create mode 100644 src/test/modules/test_injection_points/meson.build
 create mode 100644 src/test/modules/test_injection_points/sql/test_injection_points.sql
 create mode 100644 src/test/modules/test_injection_points/test_injection_points--1.0.sql
 create mode 100644 src/test/modules/test_injection_points/test_injection_points.c
 create mode 100644 src/test/modules/test_injection_points/test_injection_points.control

diff --git a/src/test/modules/Makefile b/src/test/modules/Makefile
index a18e4d28a0..7c4cefaedb 100644
--- a/src/test/modules/Makefile
+++ b/src/test/modules/Makefile
@@ -36,6 +36,13 @@ SUBDIRS = \
 		  unsafe_tests \
 		  worker_spi
 
+
+ifeq ($(enable_injection_points),yes)
+SUBDIRS += test_injection_points
+else
+ALWAYS_SUBDIRS += test_injection_points
+endif
+
 ifeq ($(with_ssl),openssl)
 SUBDIRS += ssl_passphrase_callback
 else
diff --git a/src/test/modules/meson.build b/src/test/modules/meson.build
index 4e83c0f8d7..1d6764e235 100644
--- a/src/test/modules/meson.build
+++ b/src/test/modules/meson.build
@@ -17,6 +17,7 @@ subdir('test_ddl_deparse')
 subdir('test_dsa')
 subdir('test_extensions')
 subdir('test_ginpostinglist')
+subdir('test_injection_points')
 subdir('test_integerset')
 subdir('test_lfind')
 subdir('test_misc')
diff --git a/src/test/modules/test_injection_points/.gitignore b/src/test/modules/test_injection_points/.gitignore
new file mode 100644
index 0000000000..5dcb3ff972
--- /dev/null
+++ b/src/test/modules/test_injection_points/.gitignore
@@ -0,0 +1,4 @@
+# Generated subdirectories
+/log/
+/results/
+/tmp_check/
diff --git a/src/test/modules/test_injection_points/Makefile b/src/test/modules/test_injection_points/Makefile
new file mode 100644
index 0000000000..65bcdde782
--- /dev/null
+++ b/src/test/modules/test_injection_points/Makefile
@@ -0,0 +1,22 @@
+# src/test/modules/test_injection_points/Makefile
+
+MODULE_big = test_injection_points
+OBJS = \
+	$(WIN32RES) \
+	test_injection_points.o
+PGFILEDESC = "test_injection_points - test injection points"
+
+EXTENSION = test_injection_points
+DATA = test_injection_points--1.0.sql
+REGRESS = test_injection_points
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = src/test/modules/test_injection_points
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
diff --git a/src/test/modules/test_injection_points/expected/test_injection_points.out b/src/test/modules/test_injection_points/expected/test_injection_points.out
new file mode 100644
index 0000000000..a8ddae0aad
--- /dev/null
+++ b/src/test/modules/test_injection_points/expected/test_injection_points.out
@@ -0,0 +1,117 @@
+CREATE EXTENSION test_injection_points;
+SELECT test_injection_points_attach('TestInjectionBooh', 'booh');
+ERROR:  incorrect mode "booh" for injection point creation
+SELECT test_injection_points_attach('TestInjectionError', 'error');
+ test_injection_points_attach 
+------------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_attach('TestInjectionLog', 'notice');
+ test_injection_points_attach 
+------------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_attach('TestInjectionLog2', 'notice');
+ test_injection_points_attach 
+------------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionBooh'); -- nothing
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionLog2'); -- notice
+NOTICE:  notice triggered for injection point TestInjectionLog2
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionLog'); -- notice
+NOTICE:  notice triggered for injection point TestInjectionLog
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionError'); -- error
+ERROR:  error triggered for injection point TestInjectionError
+-- Re-load and run again.
+\c
+SELECT test_injection_points_run('TestInjectionLog2'); -- notice
+NOTICE:  notice triggered for injection point TestInjectionLog2
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionLog'); -- notice
+NOTICE:  notice triggered for injection point TestInjectionLog
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionError'); -- error
+ERROR:  error triggered for injection point TestInjectionError
+-- Remove one entry and check the other one.
+SELECT test_injection_points_detach('TestInjectionError'); -- ok
+ test_injection_points_detach 
+------------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionLog'); -- notice
+NOTICE:  notice triggered for injection point TestInjectionLog
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionError'); -- nothing
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+-- All entries removed, nothing happens
+SELECT test_injection_points_detach('TestInjectionLog'); -- ok
+ test_injection_points_detach 
+------------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionLog'); -- nothing
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionError'); -- nothing
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_run('TestInjectionLog2'); -- notice
+NOTICE:  notice triggered for injection point TestInjectionLog2
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+SELECT test_injection_points_detach('TestInjectionLog'); -- fails
+ERROR:  injection point "TestInjectionLog" not found
+SELECT test_injection_points_run('TestInjectionLog2'); -- notice
+NOTICE:  notice triggered for injection point TestInjectionLog2
+ test_injection_points_run 
+---------------------------
+ 
+(1 row)
+
+DROP EXTENSION test_injection_points;
diff --git a/src/test/modules/test_injection_points/meson.build b/src/test/modules/test_injection_points/meson.build
new file mode 100644
index 0000000000..7509a102ef
--- /dev/null
+++ b/src/test/modules/test_injection_points/meson.build
@@ -0,0 +1,37 @@
+# Copyright (c) 2022-2023, PostgreSQL Global Development Group
+
+if not get_option('injection_points')
+  subdir_done()
+endif
+
+test_injection_points_sources = files(
+  'test_injection_points.c',
+)
+
+if host_system == 'windows'
+  test_injection_points_sources += rc_lib_gen.process(win32ver_rc, extra_args: [
+    '--NAME', 'test_injection_points',
+    '--FILEDESC', 'test_injection_points - test injection points',])
+endif
+
+test_injection_points = shared_module('test_injection_points',
+  test_injection_points_sources,
+  kwargs: pg_test_mod_args,
+)
+test_install_libs += test_injection_points
+
+test_install_data += files(
+  'test_injection_points.control',
+  'test_injection_points--1.0.sql',
+)
+
+tests += {
+  'name': 'test_injection_points',
+  'sd': meson.current_source_dir(),
+  'bd': meson.current_build_dir(),
+  'regress': {
+    'sql': [
+      'test_injection_points',
+    ],
+  },
+}
diff --git a/src/test/modules/test_injection_points/sql/test_injection_points.sql b/src/test/modules/test_injection_points/sql/test_injection_points.sql
new file mode 100644
index 0000000000..8f23f4c044
--- /dev/null
+++ b/src/test/modules/test_injection_points/sql/test_injection_points.sql
@@ -0,0 +1,33 @@
+CREATE EXTENSION test_injection_points;
+
+SELECT test_injection_points_attach('TestInjectionBooh', 'booh');
+SELECT test_injection_points_attach('TestInjectionError', 'error');
+SELECT test_injection_points_attach('TestInjectionLog', 'notice');
+SELECT test_injection_points_attach('TestInjectionLog2', 'notice');
+
+SELECT test_injection_points_run('TestInjectionBooh'); -- nothing
+SELECT test_injection_points_run('TestInjectionLog2'); -- notice
+SELECT test_injection_points_run('TestInjectionLog'); -- notice
+SELECT test_injection_points_run('TestInjectionError'); -- error
+
+-- Re-load and run again.
+\c
+SELECT test_injection_points_run('TestInjectionLog2'); -- notice
+SELECT test_injection_points_run('TestInjectionLog'); -- notice
+SELECT test_injection_points_run('TestInjectionError'); -- error
+
+-- Remove one entry and check the other one.
+SELECT test_injection_points_detach('TestInjectionError'); -- ok
+SELECT test_injection_points_run('TestInjectionLog'); -- notice
+SELECT test_injection_points_run('TestInjectionError'); -- nothing
+-- All entries removed, nothing happens
+SELECT test_injection_points_detach('TestInjectionLog'); -- ok
+SELECT test_injection_points_run('TestInjectionLog'); -- nothing
+SELECT test_injection_points_run('TestInjectionError'); -- nothing
+SELECT test_injection_points_run('TestInjectionLog2'); -- notice
+
+SELECT test_injection_points_detach('TestInjectionLog'); -- fails
+
+SELECT test_injection_points_run('TestInjectionLog2'); -- notice
+
+DROP EXTENSION test_injection_points;
diff --git a/src/test/modules/test_injection_points/test_injection_points--1.0.sql b/src/test/modules/test_injection_points/test_injection_points--1.0.sql
new file mode 100644
index 0000000000..1c0a689ae2
--- /dev/null
+++ b/src/test/modules/test_injection_points/test_injection_points--1.0.sql
@@ -0,0 +1,36 @@
+/* src/test/modules/test_injection_points/test_injection_points--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_injection_points" to load this file. \quit
+
+--
+-- test_injection_points_attach()
+--
+-- Attaches an injection point using callbacks from one of the predefined
+-- modes.
+--
+CREATE FUNCTION test_injection_points_attach(IN point_name TEXT,
+    IN mode text)
+RETURNS void
+AS 'MODULE_PATHNAME', 'test_injection_points_attach'
+LANGUAGE C STRICT PARALLEL UNSAFE;
+
+--
+-- test_injection_points_run()
+--
+-- Executes an injection point.
+--
+CREATE FUNCTION test_injection_points_run(IN point_name TEXT)
+RETURNS void
+AS 'MODULE_PATHNAME', 'test_injection_points_run'
+LANGUAGE C STRICT PARALLEL UNSAFE;
+
+--
+-- test_injection_points_detach()
+--
+-- Detaches an injection point.
+--
+CREATE FUNCTION test_injection_points_detach(IN point_name TEXT)
+RETURNS void
+AS 'MODULE_PATHNAME', 'test_injection_points_detach'
+LANGUAGE C STRICT PARALLEL UNSAFE;
diff --git a/src/test/modules/test_injection_points/test_injection_points.c b/src/test/modules/test_injection_points/test_injection_points.c
new file mode 100644
index 0000000000..efb2c74c47
--- /dev/null
+++ b/src/test/modules/test_injection_points/test_injection_points.c
@@ -0,0 +1,91 @@
+/*--------------------------------------------------------------------------
+ *
+ * test_injection_points.c
+ *		Code for testing injection points.
+ *
+ * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *		src/test/modules/test_injection_points/test_injection_points.c
+ *
+ * Injection points are able to trigger user-defined callbacks in pre-defined
+ * code paths.
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "fmgr.h"
+#include "utils/builtins.h"
+#include "utils/injection_point.h"
+
+PG_MODULE_MAGIC;
+
+extern PGDLLEXPORT void test_injection_error(const char *name);
+extern PGDLLEXPORT void test_injection_notice(const char *name);
+
+/* Set of callbacks available at point creation */
+void
+test_injection_error(const char *name)
+{
+	elog(ERROR, "error triggered for injection point %s", name);
+}
+
+void
+test_injection_notice(const char *name)
+{
+	elog(NOTICE, "notice triggered for injection point %s", name);
+}
+
+/*
+ * SQL function for creating an injection point.
+ */
+PG_FUNCTION_INFO_V1(test_injection_points_attach);
+Datum
+test_injection_points_attach(PG_FUNCTION_ARGS)
+{
+	char	   *name = text_to_cstring(PG_GETARG_TEXT_PP(0));
+	char	   *mode = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	char	   *function;
+
+	if (strcmp(mode, "error") == 0)
+		function = "test_injection_error";
+	else if (strcmp(mode, "notice") == 0)
+		function = "test_injection_notice";
+	else
+		elog(ERROR, "incorrect mode \"%s\" for injection point creation", mode);
+
+	InjectionPointAttach(name, "test_injection_points", function);
+
+	PG_RETURN_VOID();
+}
+
+/*
+ * SQL function for triggering an injection point.
+ */
+PG_FUNCTION_INFO_V1(test_injection_points_run);
+Datum
+test_injection_points_run(PG_FUNCTION_ARGS)
+{
+	char	   *name = text_to_cstring(PG_GETARG_TEXT_PP(0));
+
+	INJECTION_POINT(name);
+
+	PG_RETURN_VOID();
+}
+
+/*
+ * SQL function for dropping an injection point.
+ */
+PG_FUNCTION_INFO_V1(test_injection_points_detach);
+Datum
+test_injection_points_detach(PG_FUNCTION_ARGS)
+{
+	char	   *name = text_to_cstring(PG_GETARG_TEXT_PP(0));
+
+	InjectionPointDetach(name);
+
+	PG_RETURN_VOID();
+}
diff --git a/src/test/modules/test_injection_points/test_injection_points.control b/src/test/modules/test_injection_points/test_injection_points.control
new file mode 100644
index 0000000000..a13657cfc6
--- /dev/null
+++ b/src/test/modules/test_injection_points/test_injection_points.control
@@ -0,0 +1,4 @@
+comment = 'Test code for injection points'
+default_version = '1.0'
+module_pathname = '$libdir/test_injection_points'
+relocatable = true
-- 
2.42.0

From c24886fed2b5108569a50ab79edc4c4e8c1e17bb Mon Sep 17 00:00:00 2001
From: Michael Paquier <mich...@paquier.xyz>
Date: Thu, 16 Nov 2023 14:28:22 +0900
Subject: [PATCH v5 3/4] Add regression test to show snapbuild consistency

Reverting 409f9ca44713 causes the test to fail.  The test added here
relies on the existing callbacks in test_injection_points.
---
 src/backend/replication/logical/snapbuild.c   |  3 ++
 .../modules/test_injection_points/Makefile    |  2 +
 .../modules/test_injection_points/meson.build |  5 ++
 .../t/001_snapshot_status.pl                  | 47 +++++++++++++++++++
 4 files changed, 57 insertions(+)
 create mode 100644 src/test/modules/test_injection_points/t/001_snapshot_status.pl

diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index fec190a8b2..3491e5a872 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -141,6 +141,7 @@
 #include "storage/procarray.h"
 #include "storage/standby.h"
 #include "utils/builtins.h"
+#include "utils/injection_point.h"
 #include "utils/memutils.h"
 #include "utils/snapmgr.h"
 #include "utils/snapshot.h"
@@ -654,6 +655,8 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
 	snap->xcnt = newxcnt;
 	snap->xip = newxip;
 
+	INJECTION_POINT("SnapBuildInitialSnapshot");
+
 	return snap;
 }
 
diff --git a/src/test/modules/test_injection_points/Makefile b/src/test/modules/test_injection_points/Makefile
index 65bcdde782..4696c1b013 100644
--- a/src/test/modules/test_injection_points/Makefile
+++ b/src/test/modules/test_injection_points/Makefile
@@ -10,6 +10,8 @@ EXTENSION = test_injection_points
 DATA = test_injection_points--1.0.sql
 REGRESS = test_injection_points
 
+TAP_TESTS = 1
+
 ifdef USE_PGXS
 PG_CONFIG = pg_config
 PGXS := $(shell $(PG_CONFIG) --pgxs)
diff --git a/src/test/modules/test_injection_points/meson.build b/src/test/modules/test_injection_points/meson.build
index 7509a102ef..6006b38f3d 100644
--- a/src/test/modules/test_injection_points/meson.build
+++ b/src/test/modules/test_injection_points/meson.build
@@ -34,4 +34,9 @@ tests += {
       'test_injection_points',
     ],
   },
+  'tap': {
+    'tests': [
+      't/001_snapshot_status.pl',
+    ],
+  }
 }
diff --git a/src/test/modules/test_injection_points/t/001_snapshot_status.pl b/src/test/modules/test_injection_points/t/001_snapshot_status.pl
new file mode 100644
index 0000000000..ca5c6cc7a4
--- /dev/null
+++ b/src/test/modules/test_injection_points/t/001_snapshot_status.pl
@@ -0,0 +1,47 @@
+# Test consistent of initial snapshot data.
+
+# This requires a node with wal_level=logical combined with an injection
+# point that forces a failure when a snapshot is initially built with a
+# logical slot created.
+#
+# See bug https://postgr.es/m/CAFiTN-s0zA1Kj0ozGHwkYkHwa5U0zUE94RSc_g81WrpcETB5=w...@mail.gmail.com.
+
+use strict;
+use warnings;
+
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('node');
+$node->init(allows_streaming => 'logical');
+$node->start;
+
+$node->safe_psql('postgres', 'CREATE EXTENSION test_injection_points;');
+$node->safe_psql('postgres',
+  "SELECT test_injection_points_attach('SnapBuildInitialSnapshot', 'error');");
+
+my $node_host = $node->host;
+my $node_port = $node->port;
+my $connstr_common = "host=$node_host port=$node_port";
+my $connstr_db = "$connstr_common replication=database dbname=postgres";
+
+# This requires a single session, with two commands.
+my $psql_session =
+  $node->background_psql('postgres', on_error_stop => 0,
+			 extra_params => [ '-d', $connstr_db ]);
+my ($output, $ret) = $psql_session->query(
+    'CREATE_REPLICATION_SLOT "slot" LOGICAL "pgoutput";');
+ok($ret != 0, "First CREATE_REPLICATION_SLOT fails on injected error");
+
+# Now remove the injected error and check that the second command works.
+$node->safe_psql('postgres',
+  "SELECT test_injection_points_detach('SnapBuildInitialSnapshot');");
+
+($output, $ret) = $psql_session->query(
+    'CREATE_REPLICATION_SLOT "slot" LOGICAL "pgoutput";');
+print "BOO" . substr($output, 0, 4) . "\n";
+ok(substr($output, 0, 4) eq 'slot',
+   "Second CREATE_REPLICATION_SLOT passes");
+
+done_testing();
-- 
2.42.0

From 29f152482d4f41ad9bdffb57204448ba4af9801f Mon Sep 17 00:00:00 2001
From: Michael Paquier <mich...@paquier.xyz>
Date: Thu, 16 Nov 2023 14:42:31 +0900
Subject: [PATCH v5 4/4] Add basic test for promotion and restart race
 condition

This test fails after 7863ee4def65 is reverted.  test_injection_points
is extended so as it is possible to add condition variables to wait for
in the point callbacks, with a SQL function to broadcast condition
variables that may be sleeping.

I guess that this should be extended so as there is more than one
condition variable stored in shmem for this module, controlling which
variable to wait for directly in the callback itself, but that's not
really necessary now.
---
 src/backend/access/transam/xlog.c             |   7 +
 .../modules/test_injection_points/meson.build |   1 +
 .../t/002_invalid_checkpoint_after_promote.pl | 132 ++++++++++++++++++
 .../test_injection_points--1.0.sql            |  10 ++
 .../test_injection_points.c                   |  73 ++++++++++
 5 files changed, 223 insertions(+)
 create mode 100644 src/test/modules/test_injection_points/t/002_invalid_checkpoint_after_promote.pl

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 1159dff1a6..d3828bcee3 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -99,6 +99,7 @@
 #include "storage/sync.h"
 #include "utils/guc_hooks.h"
 #include "utils/guc_tables.h"
+#include "utils/injection_point.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
 #include "utils/relmapper.h"
@@ -7329,6 +7330,12 @@ CreateRestartPoint(int flags)
 
 	CheckPointGuts(lastCheckPoint.redo, flags);
 
+	/*
+	 * This location is important to be after CheckPointGuts() to ensure
+	 * that some work has happened.
+	 */
+	INJECTION_POINT("CreateRestartPoint");
+
 	/*
 	 * Remember the prior checkpoint's redo ptr for
 	 * UpdateCheckPointDistanceEstimate()
diff --git a/src/test/modules/test_injection_points/meson.build b/src/test/modules/test_injection_points/meson.build
index 6006b38f3d..6ebdc728b7 100644
--- a/src/test/modules/test_injection_points/meson.build
+++ b/src/test/modules/test_injection_points/meson.build
@@ -37,6 +37,7 @@ tests += {
   'tap': {
     'tests': [
       't/001_snapshot_status.pl',
+      't/002_invalid_checkpoint_after_promote.pl',
     ],
   }
 }
diff --git a/src/test/modules/test_injection_points/t/002_invalid_checkpoint_after_promote.pl b/src/test/modules/test_injection_points/t/002_invalid_checkpoint_after_promote.pl
new file mode 100644
index 0000000000..2da243e871
--- /dev/null
+++ b/src/test/modules/test_injection_points/t/002_invalid_checkpoint_after_promote.pl
@@ -0,0 +1,132 @@
+use strict;
+use warnings;
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Time::HiRes qw(usleep nanosleep);
+use Test::More;
+
+# initialize primary node
+my $node_primary = PostgreSQL::Test::Cluster->new('master');
+$node_primary->init(allows_streaming => 1);
+$node_primary->append_conf(
+	'postgresql.conf', q[
+checkpoint_timeout = 30s
+log_checkpoints = on
+restart_after_crash = on
+]);
+$node_primary->start;
+my $backup_name = 'my_backup';
+$node_primary->backup($backup_name);
+
+# setup a standby
+my $node_standby = PostgreSQL::Test::Cluster->new('standby1');
+$node_standby->init_from_backup($node_primary, $backup_name, has_streaming => 1);
+$node_standby->start;
+
+# dummy table for the upcoming tests.
+$node_primary->safe_psql('postgres', 'checkpoint');
+$node_primary->safe_psql('postgres', 'CREATE TABLE prim_tab (a int);');
+
+# Register a injection point on the standby so as the follow-up
+# restart point running on it will wait.
+$node_primary->safe_psql('postgres', 'CREATE EXTENSION test_injection_points;');
+# Wait until the extension has been created on the standby
+$node_primary->wait_for_replay_catchup($node_standby);
+# This causes a restartpoint to wait on a standby.
+$node_standby->safe_psql('postgres',
+  "SELECT test_injection_points_attach('CreateRestartPoint', 'wait');");
+
+# Execute a restart point on the standby, that will be waited on.
+# This needs to be in the background as we'll wait on it.
+my $logstart = -s $node_standby->logfile;
+my $psql_session =
+  $node_standby->background_psql('postgres', on_error_stop => 0);
+$psql_session->query_until(qr/starting_checkpoint/, q(
+   \echo starting_checkpoint
+   CHECKPOINT;
+));
+
+# Switch one WAL segment to make the restartpoint remove it.
+$node_primary->safe_psql('postgres', 'INSERT INTO prim_tab VALUES (1);');
+$node_primary->safe_psql('postgres', 'SELECT pg_switch_wal();');
+$node_primary->wait_for_replay_catchup($node_standby);
+
+# Wait until the checkpointer is in the middle of the restartpoint
+# processing.
+ok( $node_standby->poll_query_until(
+	'postgres',
+	qq[SELECT count(*) FROM pg_stat_activity
+           WHERE backend_type = 'checkpointer' AND wait_event = 'test_injection_wait' ;],
+	'1'),
+    'checkpointer is waiting at restart point'
+    ) or die "Timed out while waiting for checkpointer to run restartpoint";
+
+
+# Restartpoint should have started on standby.
+my $log = slurp_file($node_standby->logfile, $logstart);
+my $checkpoint_start = 0;
+if ($log =~ m/restartpoint starting: immediate wait/)
+{
+	$checkpoint_start = 1;
+}
+is($checkpoint_start, 1, 'restartpoint has started');
+
+# promote during restartpoint
+$node_primary->stop;
+$node_standby->promote;
+
+# Update the start position before waking up the checkpointer!
+$logstart = -s $node_standby->logfile;
+
+# Now wake up the checkpointer
+$node_standby->safe_psql('postgres',
+  "SELECT test_injection_points_wake();");
+
+# wait until checkpoint completes on the newly-promoted standby.
+my $checkpoint_complete = 0;
+for (my $i = 0; $i < 3000; $i++)
+{
+	my $log = slurp_file($node_standby->logfile, $logstart);
+	if ($log =~ m/restartpoint complete/)
+	{
+		$checkpoint_complete = 1;
+		last;
+	}
+	usleep(100_000);
+}
+is($checkpoint_complete, 1, 'restartpoint has completed');
+
+# kill SIGKILL a backend, and all backend will restart. Note that previous checkpoint has not completed.
+my $psql_timeout = IPC::Run::timer(3600);
+my ($killme_stdin, $killme_stdout, $killme_stderr) = ('', '', '');
+my $killme = IPC::Run::start(
+	[ 'psql', '-XAtq', '-v', 'ON_ERROR_STOP=1', '-f', '-', '-d', $node_standby->connstr('postgres') ],
+	'<',
+	\$killme_stdin,
+	'>',
+	\$killme_stdout,
+	'2>',
+	\$killme_stderr,
+	$psql_timeout);
+$killme_stdin .= q[
+SELECT pg_backend_pid();
+];
+$killme->pump until $killme_stdout =~ /[[:digit:]]+[\r\n]$/;
+my $pid = $killme_stdout;
+chomp($pid);
+my $ret = PostgreSQL::Test::Utils::system_log('pg_ctl', 'kill', 'KILL', $pid);
+is($ret, 0, 'killed process with KILL');
+my $stdout;
+my $stderr;
+
+# after recovery, the server will not start, and log PANIC: could not locate a valid checkpoint record
+for (my $i = 0; $i < 30; $i++)
+{
+    ($ret, $stdout, $stderr) = $node_standby->psql('postgres', 'select 1');
+    last if $ret == 0;
+	sleep(1);
+}
+is($ret, 0, "psql connect success");
+is($stdout, 1, "psql select 1");
+
+done_testing();
diff --git a/src/test/modules/test_injection_points/test_injection_points--1.0.sql b/src/test/modules/test_injection_points/test_injection_points--1.0.sql
index 1c0a689ae2..05f97f0982 100644
--- a/src/test/modules/test_injection_points/test_injection_points--1.0.sql
+++ b/src/test/modules/test_injection_points/test_injection_points--1.0.sql
@@ -25,6 +25,16 @@ RETURNS void
 AS 'MODULE_PATHNAME', 'test_injection_points_run'
 LANGUAGE C STRICT PARALLEL UNSAFE;
 
+--
+-- test_injection_points_wake()
+--
+-- Wakes a condition variable executed in an injection point.
+--
+CREATE FUNCTION test_injection_points_wake()
+RETURNS void
+AS 'MODULE_PATHNAME', 'test_injection_points_wake'
+LANGUAGE C STRICT PARALLEL UNSAFE;
+
 --
 -- test_injection_points_detach()
 --
diff --git a/src/test/modules/test_injection_points/test_injection_points.c b/src/test/modules/test_injection_points/test_injection_points.c
index efb2c74c47..8b837d85d3 100644
--- a/src/test/modules/test_injection_points/test_injection_points.c
+++ b/src/test/modules/test_injection_points/test_injection_points.c
@@ -18,13 +18,56 @@
 #include "postgres.h"
 
 #include "fmgr.h"
+#include "storage/condition_variable.h"
+#include "storage/lwlock.h"
+#include "storage/shmem.h"
 #include "utils/builtins.h"
 #include "utils/injection_point.h"
+#include "utils/wait_event.h"
 
 PG_MODULE_MAGIC;
 
+/* Shared state information for injection points. */
+typedef struct TestInjectionPointSharedState
+{
+	/*
+	 * Wait variable that can be registered at a given point, and that can be
+	 * awakened via SQL.
+	 */
+	ConditionVariable	wait_point;
+} TestInjectionPointSharedState;
+
+/* Pointer to shared-memory state. */
+static TestInjectionPointSharedState *inj_state = NULL;
+
+/* Wait event when waiting on condition variable */
+static uint32 test_injection_wait_event = 0;
+
 extern PGDLLEXPORT void test_injection_error(const char *name);
 extern PGDLLEXPORT void test_injection_notice(const char *name);
+extern PGDLLEXPORT void test_injection_wait(const char *name);
+
+
+static void
+test_injection_init_shmem(void)
+{
+	bool		found;
+
+	if (inj_state != NULL)
+		return;
+
+	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
+	inj_state = ShmemInitStruct("test_injection_points",
+								sizeof(TestInjectionPointSharedState),
+								&found);
+	if (!found)
+	{
+		/* First time through ... */
+		MemSet(inj_state, 0, sizeof(TestInjectionPointSharedState));
+		ConditionVariableInit(&inj_state->wait_point);
+	}
+	LWLockRelease(AddinShmemInitLock);
+}
 
 /* Set of callbacks available at point creation */
 void
@@ -39,6 +82,20 @@ test_injection_notice(const char *name)
 	elog(NOTICE, "notice triggered for injection point %s", name);
 }
 
+void
+test_injection_wait(const char *name)
+{
+	if (inj_state == NULL)
+		test_injection_init_shmem();
+	if (test_injection_wait_event == 0)
+		test_injection_wait_event = WaitEventExtensionNew("test_injection_wait");
+
+	/* And sleep.. */
+	ConditionVariablePrepareToSleep(&inj_state->wait_point);
+	ConditionVariableSleep(&inj_state->wait_point, test_injection_wait_event);
+	ConditionVariableCancelSleep();
+}
+
 /*
  * SQL function for creating an injection point.
  */
@@ -54,6 +111,8 @@ test_injection_points_attach(PG_FUNCTION_ARGS)
 		function = "test_injection_error";
 	else if (strcmp(mode, "notice") == 0)
 		function = "test_injection_notice";
+	else if (strcmp(mode, "wait") == 0)
+		function = "test_injection_wait";
 	else
 		elog(ERROR, "incorrect mode \"%s\" for injection point creation", mode);
 
@@ -76,6 +135,20 @@ test_injection_points_run(PG_FUNCTION_ARGS)
 	PG_RETURN_VOID();
 }
 
+/*
+ * SQL function for waking a condition variable.
+ */
+PG_FUNCTION_INFO_V1(test_injection_points_wake);
+Datum
+test_injection_points_wake(PG_FUNCTION_ARGS)
+{
+	if (inj_state == NULL)
+		test_injection_init_shmem();
+
+	ConditionVariableBroadcast(&inj_state->wait_point);
+	PG_RETURN_VOID();
+}
+
 /*
  * SQL function for dropping an injection point.
  */
-- 
2.42.0

Attachment: signature.asc
Description: PGP signature

Reply via email to