trimheapfreemeory.patch

diff --git a/src/backend/catalog/system_functions.sql b/src/backend/catalog/system_functions.sql
index 623b9539b1..3aa3b60288 100644
--- a/src/backend/catalog/system_functions.sql
+++ b/src/backend/catalog/system_functions.sql
@@ -754,6 +754,8 @@ REVOKE EXECUTE ON FUNCTION pg_ls_dir(text,boolean,boolean) FROM public;
 
 REVOKE EXECUTE ON FUNCTION pg_log_backend_memory_contexts(integer) FROM PUBLIC;
 
+REVOKE EXECUTE ON FUNCTION pg_trim_backend_heap_free_memory(integer) FROM PUBLIC;
+
 REVOKE EXECUTE ON FUNCTION pg_ls_logicalsnapdir() FROM PUBLIC;
 
 REVOKE EXECUTE ON FUNCTION pg_ls_logicalmapdir() FROM PUBLIC;
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 7d0877c95e..d90d1649a1 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -765,6 +765,10 @@ HandleAutoVacLauncherInterrupts(void)
 	if (LogMemoryContextPending)
 		ProcessLogMemoryContextInterrupt();
 
+	/* Perform trimming heap free memory of this process */
+	if (TrimHeapFreeMemoryPending)
+		ProcessTrimHeapFreeMemoryInterrupt();
+
 	/* Process sinval catchup interrupts that happened while sleeping */
 	ProcessCatchupInterrupt();
 }
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 199f008bcd..2109f9e822 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -605,6 +605,10 @@ HandleCheckpointerInterrupts(void)
 	/* Perform logging of memory contexts of this process */
 	if (LogMemoryContextPending)
 		ProcessLogMemoryContextInterrupt();
+
+	/* Perform trimming heap free memory of this process */
+	if (TrimHeapFreeMemoryPending)
+		ProcessTrimHeapFreeMemoryInterrupt();
 }
 
 /*
diff --git a/src/backend/postmaster/interrupt.c b/src/backend/postmaster/interrupt.c
index eedc0980cf..4389ff3d48 100644
--- a/src/backend/postmaster/interrupt.c
+++ b/src/backend/postmaster/interrupt.c
@@ -48,6 +48,10 @@ HandleMainLoopInterrupts(void)
 	/* Perform logging of memory contexts of this process */
 	if (LogMemoryContextPending)
 		ProcessLogMemoryContextInterrupt();
+
+	/* Perform trimming heap free memory of this process */
+	if (TrimHeapFreeMemoryPending)
+		ProcessTrimHeapFreeMemoryInterrupt();
 }
 
 /*
diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index 02f91431f5..cd72412614 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -865,6 +865,10 @@ HandlePgArchInterrupts(void)
 	if (LogMemoryContextPending)
 		ProcessLogMemoryContextInterrupt();
 
+	/* Perform trimming heap free memory of this process */
+	if (TrimHeapFreeMemoryPending)
+		ProcessTrimHeapFreeMemoryInterrupt();
+
 	if (ConfigReloadPending)
 	{
 		char	   *archiveLib = pstrdup(XLogArchiveLibrary);
diff --git a/src/backend/postmaster/startup.c b/src/backend/postmaster/startup.c
index ef6f98ebcd..5eb8d168e7 100644
--- a/src/backend/postmaster/startup.c
+++ b/src/backend/postmaster/startup.c
@@ -192,6 +192,10 @@ HandleStartupProcInterrupts(void)
 	/* Perform logging of memory contexts of this process */
 	if (LogMemoryContextPending)
 		ProcessLogMemoryContextInterrupt();
+
+	/* Perform trimming heap free memory of this process */
+	if (TrimHeapFreeMemoryPending)
+		ProcessTrimHeapFreeMemoryInterrupt();
 }
 
 
diff --git a/src/backend/postmaster/walsummarizer.c b/src/backend/postmaster/walsummarizer.c
index daa7909382..d167e41291 100644
--- a/src/backend/postmaster/walsummarizer.c
+++ b/src/backend/postmaster/walsummarizer.c
@@ -874,6 +874,10 @@ HandleWalSummarizerInterrupts(void)
 	/* Perform logging of memory contexts of this process */
 	if (LogMemoryContextPending)
 		ProcessLogMemoryContextInterrupt();
+
+	/* Perform trimming heap free memory of this process */
+	if (TrimHeapFreeMemoryPending)
+		ProcessTrimHeapFreeMemoryInterrupt();
 }
 
 /*
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 87027f27eb..3251d2823e 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -712,6 +712,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		HandleRecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
+	if (CheckProcSignal(PROCSIG_TRIM_HEAP_FREE_MEMORY))
+		HandleTrimHeapFreeMemoryInterrupt();
+
 	SetLatch(MyLatch);
 }
 
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 8bc6bea113..f90a557bbe 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3479,6 +3479,9 @@ ProcessInterrupts(void)
 
 	if (ParallelApplyMessagePending)
 		HandleParallelApplyMessages();
+
+	if (TrimHeapFreeMemoryPending)
+		ProcessTrimHeapFreeMemoryInterrupt();
 }
 
 /*
diff --git a/src/backend/utils/adt/mcxtfuncs.c b/src/backend/utils/adt/mcxtfuncs.c
index 6a6634e1cd..c213c4163a 100644
--- a/src/backend/utils/adt/mcxtfuncs.c
+++ b/src/backend/utils/adt/mcxtfuncs.c
@@ -305,3 +305,57 @@ pg_log_backend_memory_contexts(PG_FUNCTION_ARGS)
 
 	PG_RETURN_BOOL(true);
 }
+
+/*
+ * pg_trim_backend_heap_free_memory
+ *		Signal a backend or an auxiliary process to trim heap free memory.
+ *
+ * On receipt of this signal, a backend or an auxiliary process sets the flag
+ * in the signal handler, which causes the next CHECK_FOR_INTERRUPTS()
+ * or process-specific interrupt handler to log the memory contexts.
+ */
+Datum
+pg_trim_backend_heap_free_memory(PG_FUNCTION_ARGS)
+{
+	int			pid = PG_GETARG_INT32(0);
+	PGPROC	   *proc;
+	ProcNumber	procNumber = INVALID_PROC_NUMBER;
+
+	/*
+	 * See if the process with given pid is a backend or an auxiliary process.
+	 */
+	proc = BackendPidGetProc(pid);
+	if (proc == NULL)
+		proc = AuxiliaryPidGetProc(pid);
+
+	/*
+	 * BackendPidGetProc() and AuxiliaryPidGetProc() return NULL if the pid
+	 * isn't valid; but by the time we reach kill(), a process for which we
+	 * get a valid proc here might have terminated on its own.  There's no way
+	 * to acquire a lock on an arbitrary process to prevent that. But since
+	 * this mechanism is usually used to debug a backend or an auxiliary
+	 * process running and consuming lots of memory, that it might end on its
+	 * own first and its memory contexts are not logged is not a problem.
+	 */
+	if (proc == NULL)
+	{
+		/*
+		 * This is just a warning so a loop-through-resultset will not abort
+		 * if one backend terminated on its own during the run.
+		 */
+		ereport(WARNING,
+				(errmsg("PID %d is not a PostgreSQL server process", pid)));
+		PG_RETURN_BOOL(false);
+	}
+
+	procNumber = GetNumberFromPGProc(proc);
+	if (SendProcSignal(pid, PROCSIG_TRIM_HEAP_FREE_MEMORY, procNumber) < 0)
+	{
+		/* Again, just a warning to allow loops */
+		ereport(WARNING,
+				(errmsg("could not send signal to process %d: %m", pid)));
+		PG_RETURN_BOOL(false);
+	}
+
+	PG_RETURN_BOOL(true);
+}
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 03a54451ac..e90a61affe 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -39,6 +39,7 @@ volatile sig_atomic_t IdleSessionTimeoutPending = false;
 volatile sig_atomic_t ProcSignalBarrierPending = false;
 volatile sig_atomic_t LogMemoryContextPending = false;
 volatile sig_atomic_t IdleStatsUpdateTimeoutPending = false;
+volatile sig_atomic_t TrimHeapFreeMemoryPending = false;
 volatile uint32 InterruptHoldoffCount = 0;
 volatile uint32 QueryCancelHoldoffCount = 0;
 volatile uint32 CritSectionCount = 0;
diff --git a/src/backend/utils/mmgr/Makefile b/src/backend/utils/mmgr/Makefile
index 01a1fb8527..395f119d77 100644
--- a/src/backend/utils/mmgr/Makefile
+++ b/src/backend/utils/mmgr/Makefile
@@ -21,6 +21,7 @@ OBJS = \
 	generation.o \
 	mcxt.o \
 	memdebug.o \
+	memtrim.o \
 	portalmem.o \
 	slab.o
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 4abc6d9526..6186d9247d 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -8348,6 +8348,12 @@
   prorettype => 'bool', proargtypes => 'int4',
   prosrc => 'pg_log_backend_memory_contexts' },
 
+# logging memory contexts of the specified backend
+{ oid => '4551', descr => 'Trim Heap free memory of the specified backend',
+  proname => 'pg_trim_backend_heap_free_memory', provolatile => 'v',
+  prorettype => 'bool', proargtypes => 'int4',
+  prosrc => 'pg_trim_backend_heap_free_memory' },
+
 # non-persistent series generator
 { oid => '1066', descr => 'non-persistent series generator',
   proname => 'generate_series', prorows => '1000',
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 25348e71eb..5a676eeb9e 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -100,6 +100,8 @@ extern PGDLLIMPORT volatile sig_atomic_t IdleStatsUpdateTimeoutPending;
 extern PGDLLIMPORT volatile sig_atomic_t CheckClientConnectionPending;
 extern PGDLLIMPORT volatile sig_atomic_t ClientConnectionLost;
 
+extern PGDLLIMPORT volatile sig_atomic_t TrimHeapFreeMemoryPending;
+
 /* these are marked volatile because they are examined by signal handlers: */
 extern PGDLLIMPORT volatile uint32 InterruptHoldoffCount;
 extern PGDLLIMPORT volatile uint32 QueryCancelHoldoffCount;
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index f94c11a9a8..0d4a3a42a2 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -48,6 +48,8 @@ typedef enum
 	PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 	PROCSIG_RECOVERY_CONFLICT_LAST = PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
+	PROCSIG_TRIM_HEAP_FREE_MEMORY, /* ask backend to release free memory from the heap */
+
 	NUM_PROCSIGNALS				/* Must be last! */
 } ProcSignalReason;
 
diff --git a/src/include/utils/memutils.h b/src/include/utils/memutils.h
index cd9596ff21..61d4d6d252 100644
--- a/src/include/utils/memutils.h
+++ b/src/include/utils/memutils.h
@@ -104,6 +104,9 @@ extern void MemoryContextCheck(MemoryContext context);
 extern void HandleLogMemoryContextInterrupt(void);
 extern void ProcessLogMemoryContextInterrupt(void);
 
+extern void HandleTrimHeapFreeMemoryInterrupt(void);
+extern void ProcessTrimHeapFreeMemoryInterrupt(void);
+
 /*
  * Memory-context-type-specific functions
  */
diff --git a/src/test/regress/expected/misc_functions.out b/src/test/regress/expected/misc_functions.out
index 35fb72f302..9bde10b2b1 100644
--- a/src/test/regress/expected/misc_functions.out
+++ b/src/test/regress/expected/misc_functions.out
@@ -365,6 +365,17 @@ RESET ROLE;
 REVOKE EXECUTE ON FUNCTION pg_log_backend_memory_contexts(integer)
   FROM regress_log_memory;
 DROP ROLE regress_log_memory;
+--
+-- pg_trim_backend_heap_free_memory()
+--
+-- Trim the heap free memory.
+--
+SELECT pg_trim_backend_heap_free_memory(pg_backend_pid());
+ pg_trim_backend_heap_free_memory 
+----------------------------------
+ t
+(1 row)
+
 --
 -- Test some built-in SRFs
 --
diff --git a/src/test/regress/sql/misc_functions.sql b/src/test/regress/sql/misc_functions.sql
index e570783453..d1cd2440ee 100644
--- a/src/test/regress/sql/misc_functions.sql
+++ b/src/test/regress/sql/misc_functions.sql
@@ -143,6 +143,14 @@ REVOKE EXECUTE ON FUNCTION pg_log_backend_memory_contexts(integer)
 
 DROP ROLE regress_log_memory;
 
+--
+-- pg_trim_backend_heap_free_memory()
+--
+-- Trim the heap free memory.
+--
+
+SELECT pg_trim_backend_heap_free_memory(pg_backend_pid());
+
 --
 -- Test some built-in SRFs
 --