Add get_pin_limit_hook

src/backend/storage/buffer/bufmgr.c

@@ -66,6 +66,7 @@
 #include "utils/resowner.h"
 #include "utils/timestamp.h"
 
+uint32 (*get_pin_limit_hook)(void);
 
 /* Note: these two macros only work on shared buffers, not local ones! */
 #define BufHdrGetBlock(bufHdr)	((Block) (BufferBlocks + ((Size) (bufHdr)->buf_id) * BLCKSZ))
@@ -2131,7 +2132,7 @@ LimitAdditionalPins(uint32 *additional_pins)
 		return;
 
 	max_backends = MaxBackends + NUM_AUXILIARY_PROCS;
-	max_proportional_pins = NBuffers / max_backends;
+	max_proportional_pins = get_pin_limit_hook ? get_pin_limit_hook() : NBuffers / max_backends;
 
 	/*
 	 * Subtract the approximate number of buffers already pinned by this

src/backend/tcop/postgres.c

@@ -107,6 +107,10 @@ int			client_connection_check_interval = 0;
 /* flags for non-system relation kinds to restrict use */
 int			restrict_nonsystem_relation_kind;
 
+#ifdef USE_INJECTION_POINTS
+/* Counter which can show us if we are in SMGR */
+int         inside_smgr_api = 0;
+#endif
 /* ----------------
  *		private typedefs etc
  * ----------------
@@ -3275,6 +3279,12 @@ ProcessInterrupts(void)
 	/* OK to accept any interrupts now? */
 	if (InterruptHoldoffCount != 0 || CritSectionCount != 0)
 		return;
+#ifdef USE_INJECTION_POINTS
+	if (inside_smgr_api > 0)
+	{
+		INJECTION_POINT("SMGR_API");
+	}
+#endif
 	InterruptPending = false;
 
 retry:

src/include/postgres.h

@@ -577,3 +577,8 @@ extern Datum Float8GetDatum(float8 X);
 #endif
 
 #endif							/* POSTGRES_H */
+
+/* Declare for neon use */
+#ifdef USE_INJECTION_POINTS
+extern int inside_smgr_api;
+#endif

src/include/storage/bufmgr.h

@@ -325,6 +325,7 @@ extern int	GetAccessStrategyPinLimit(BufferAccessStrategy strategy);
 
 extern void FreeAccessStrategy(BufferAccessStrategy strategy);
 
+extern uint32 (*get_pin_limit_hook)(void);
 
 /* inline functions */
 

src/test/modules/injection_points/injection_points.c

@@ -16,6 +16,7 @@
  */
 
 #include "postgres.h"
+#include <time.h>
 
 #include "fmgr.h"
 #include "miscadmin.h"
@@ -59,6 +60,8 @@ typedef struct InjectionPointCondition
 
 	/* ID of the process where the injection point is allowed to run */
 	int			pid;
+	/* probability in [0,1], 1.0 = always */
+	double		prob;
 } InjectionPointCondition;
 
 /*
@@ -88,13 +91,16 @@ static InjectionPointSharedState *inj_state = NULL;
 
 extern PGDLLEXPORT void injection_error(const char *name,
 										const void *private_data);
+extern PGDLLEXPORT void injection_error_prob(const char *name,
+											 const void *private_data);
 extern PGDLLEXPORT void injection_notice(const char *name,
 										 const void *private_data);
 extern PGDLLEXPORT void injection_wait(const char *name,
 									   const void *private_data);
 
 /* track if injection points attached in this process are linked to it */
 static bool injection_point_local = false;
+static double action2prob(const char *action, int pos);
 
 /*
  * Callback for shared memory area initialization.
@@ -184,7 +190,20 @@ injection_error(const char *name, const void *private_data)
 
 	elog(ERROR, "error triggered for injection point %s", name);
 }
+void
+injection_error_prob(const char *name, const void *private_data)
+{
+	InjectionPointCondition *condition = (InjectionPointCondition *) private_data;
 
+	if (!injection_point_allowed(condition))
+		return;
+
+	/* Use the probability stored in the condition. */
+	if ((double) rand() / (double) RAND_MAX > condition->prob)
+		return;
+
+	elog(ERROR, "error triggered for injection point %s", name);
+}
 void
 injection_notice(const char *name, const void *private_data)
 {
@@ -278,6 +297,11 @@ injection_points_attach(PG_FUNCTION_ARGS)
 		function = "injection_notice";
 	else if (strcmp(action, "wait") == 0)
 		function = "injection_wait";
+	else if (strncmp(action, "error-prob-", 11) == 0)
+		{
+		condition.prob = action2prob(action, 11);
+		function = "injection_error_prob";
+		}
 	else
 		elog(ERROR, "incorrect action \"%s\" for injection point creation", action);
 
@@ -402,3 +426,29 @@ injection_points_detach(PG_FUNCTION_ARGS)
 
 	PG_RETURN_VOID();
 }
+
+/*
+ * Coverts the action name into probability
+ */
+static double action2prob(const char *action, const int pos)
+{
+	/*
+	 * Simple parser: convert "0-01" -> "0.01" then strtod().
+	 */
+	const char *p = action + pos; /* points to "0-01" */
+	double prob;
+	char *endptr;
+	char buf[32];
+	int  i, j;
+
+	for (i = 0, j = 0; p[i] != '\0' && j < (int) sizeof(buf) - 1; i++)
+	{
+		buf[j++] = (p[i] == '-') ? '.' : p[i];
+	}
+	buf[j] = '\0';
+	errno = 0;
+	prob = strtod(buf, &endptr);
+	if (errno != 0 || endptr == buf || prob < 0.0 || prob > 1.0)
+		elog(ERROR, "invalid probability in action \"%s\"", action);
+	return prob;
+}