Refactor shmem initialization in Neon extension (#12630)

## Problem

Initializing of shared memory in extension is complex and non-portable.
In neon extension this boilerplate code is duplicated in several files.

## Summary of changes

Perform all initialization in one place - neon.c
All other module procvide *ShmemRequest() and *ShmemInit() fuinction
which are called from neon.c

---------

Co-authored-by: Kosntantin Knizhnik <konstantin.knizhnik@databricks.com>
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>

pgxn/neon/file_cache.c

@@ -219,10 +219,6 @@ static char *lfc_path;
 static uint64 lfc_generation;
 static FileCacheControl *lfc_ctl;
 static bool lfc_do_prewarm;
-static shmem_startup_hook_type prev_shmem_startup_hook;
-#if PG_VERSION_NUM>=150000
-static shmem_request_hook_type prev_shmem_request_hook;
-#endif
 
 bool lfc_store_prefetch_result;
 bool lfc_prewarm_update_ws_estimation;
@@ -342,18 +338,14 @@ lfc_ensure_opened(void)
 	return true;
 }
 
-static void
-lfc_shmem_startup(void)
+void
+LfcShmemInit(void)
 {
 	bool		found;
 	static HASHCTL info;
 
-	if (prev_shmem_startup_hook)
-	{
-		prev_shmem_startup_hook();
-	}
-
-	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
+	if (lfc_max_size <= 0)
+		return;
 
 	lfc_ctl = (FileCacheControl *) ShmemInitStruct("lfc", sizeof(FileCacheControl), &found);
 	if (!found)
@@ -398,19 +390,16 @@ lfc_shmem_startup(void)
 			ConditionVariableInit(&lfc_ctl->cv[i]);
 
 	}
-	LWLockRelease(AddinShmemInitLock);
 }
 
-static void
-lfc_shmem_request(void)
+void
+LfcShmemRequest(void)
 {
-#if PG_VERSION_NUM>=150000
-	if (prev_shmem_request_hook)
-		prev_shmem_request_hook();
-#endif
-
-	RequestAddinShmemSpace(sizeof(FileCacheControl) + hash_estimate_size(SIZE_MB_TO_CHUNKS(lfc_max_size) + 1, FILE_CACHE_ENRTY_SIZE));
-	RequestNamedLWLockTranche("lfc_lock", 1);
+	if (lfc_max_size > 0)
+	{
+		RequestAddinShmemSpace(sizeof(FileCacheControl) + hash_estimate_size(SIZE_MB_TO_CHUNKS(lfc_max_size) + 1, FILE_CACHE_ENRTY_SIZE));
+		RequestNamedLWLockTranche("lfc_lock", 1);
+	}
 }
 
 static bool
@@ -642,18 +631,6 @@ lfc_init(void)
 							NULL,
 							NULL,
 							NULL);
-
-	if (lfc_max_size == 0)
-		return;
-
-	prev_shmem_startup_hook = shmem_startup_hook;
-	shmem_startup_hook = lfc_shmem_startup;
-#if PG_VERSION_NUM>=150000
-	prev_shmem_request_hook = shmem_request_hook;
-	shmem_request_hook = lfc_shmem_request;
-#else
-	lfc_shmem_request();
-#endif
 }
 
 FileCacheState*

pgxn/neon/libpagestore.c

@@ -118,10 +118,6 @@ typedef struct
 	ShardMap	shard_map;
 } PagestoreShmemState;
 
-#if PG_VERSION_NUM >= 150000
-static shmem_request_hook_type prev_shmem_request_hook = NULL;
-#endif
-static shmem_startup_hook_type prev_shmem_startup_hook;
 static PagestoreShmemState *pagestore_shared;
 static uint64 pagestore_local_counter = 0;
 
@@ -1284,18 +1280,12 @@ check_neon_id(char **newval, void **extra, GucSource source)
 	return **newval == '\0' || HexDecodeString(id, *newval, 16);
 }
 
-static Size
-PagestoreShmemSize(void)
-{
-	return add_size(sizeof(PagestoreShmemState), NeonPerfCountersShmemSize());
-}
 
-static bool
+void
 PagestoreShmemInit(void)
 {
 	bool		found;
 
-	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
 	pagestore_shared = ShmemInitStruct("libpagestore shared state",
 									   sizeof(PagestoreShmemState),
 									   &found);
@@ -1306,44 +1296,12 @@ PagestoreShmemInit(void)
 		memset(&pagestore_shared->shard_map, 0, sizeof(ShardMap));
 		AssignPageserverConnstring(page_server_connstring, NULL);
 	}
-
-	NeonPerfCountersShmemInit();
-
-	LWLockRelease(AddinShmemInitLock);
-	return found;
 }
 
-static void
-pagestore_shmem_startup_hook(void)
+void
+PagestoreShmemRequest(void)
 {
-	if (prev_shmem_startup_hook)
-		prev_shmem_startup_hook();
-
-	PagestoreShmemInit();
-}
-
-static void
-pagestore_shmem_request(void)
-{
-#if PG_VERSION_NUM >= 150000
-	if (prev_shmem_request_hook)
-		prev_shmem_request_hook();
-#endif
-
-	RequestAddinShmemSpace(PagestoreShmemSize());
-}
-
-static void
-pagestore_prepare_shmem(void)
-{
-#if PG_VERSION_NUM >= 150000
-	prev_shmem_request_hook = shmem_request_hook;
-	shmem_request_hook = pagestore_shmem_request;
-#else
-	pagestore_shmem_request();
-#endif
-	prev_shmem_startup_hook = shmem_startup_hook;
-	shmem_startup_hook = pagestore_shmem_startup_hook;
+	RequestAddinShmemSpace(sizeof(PagestoreShmemState));
 }
 
 /*
@@ -1352,8 +1310,6 @@ pagestore_prepare_shmem(void)
 void
 pg_init_libpagestore(void)
 {
-	pagestore_prepare_shmem();
-
 	DefineCustomStringVariable("neon.pageserver_connstring",
 							   "connection string to the page server",
 							   NULL,
@@ -1504,8 +1460,6 @@ pg_init_libpagestore(void)
 							0,
 							NULL, NULL, NULL);
 
-	relsize_hash_init();
-
 	if (page_server != NULL)
 		neon_log(ERROR, "libpagestore already loaded");
 

pgxn/neon/neon.c

@@ -22,6 +22,7 @@
 #include "replication/slot.h"
 #include "replication/walsender.h"
 #include "storage/proc.h"
+#include "storage/ipc.h"
 #include "funcapi.h"
 #include "access/htup_details.h"
 #include "utils/builtins.h"
@@ -59,11 +60,15 @@ static ExecutorEnd_hook_type prev_ExecutorEnd = NULL;
 static void neon_ExecutorStart(QueryDesc *queryDesc, int eflags);
 static void neon_ExecutorEnd(QueryDesc *queryDesc);
 
-#if PG_MAJORVERSION_NUM >= 16
 static shmem_startup_hook_type prev_shmem_startup_hook;
-
 static void neon_shmem_startup_hook(void);
+static void neon_shmem_request_hook(void);
+
+#if PG_MAJORVERSION_NUM >= 15
+static shmem_request_hook_type prev_shmem_request_hook = NULL;
 #endif
+
+
 #if PG_MAJORVERSION_NUM >= 17
 uint32		WAIT_EVENT_NEON_LFC_MAINTENANCE;
 uint32		WAIT_EVENT_NEON_LFC_READ;
@@ -450,15 +455,44 @@ _PG_init(void)
 	 */
 #if PG_VERSION_NUM >= 160000
 	load_file("$libdir/neon_rmgr", false);
-
-	prev_shmem_startup_hook = shmem_startup_hook;
-	shmem_startup_hook = neon_shmem_startup_hook;
 #endif
 
 	/* dummy call to a Rust function in the communicator library, to check that it works */
 	(void) communicator_dummy(123);
 
+	/*
+	 * Initializing a pre-loaded Postgres extension happens in three stages:
+	 *
+	 * 1. _PG_init() is called early at postmaster startup. In this stage, no
+	 *    shared memory has been allocated yet. Core Postgres GUCs have been
+	 *    initialized from the config files, but notably, MaxBackends has not
+	 *    calculated yet. In this stage, we must register any extension GUCs
+	 *    and can do other early initialization that doesn't depend on shared
+	 *    memory. In this stage we must also register "shmem request" and
+	 *    "shmem starutup" hooks, to be called in stages 2 and 3.
+	 *
+	 * 2. After MaxBackends have been calculated, the "shmem request" hooks
+	 *    are called. The hooks can reserve shared memory by calling
+	 *    RequestAddinShmemSpace and RequestNamedLWLockTranche().  The "shmem
+	 *    request hooks" are a new mechanism in Postgres v15. In v14 and
+	 *    below, you had to make those Requests in stage 1 already, which
+	 *    means they could not depend on MaxBackends. (See hack in
+	 *    NeonPerfCountersShmemRequest())
+	 *
+	 * 3. After some more runtime-computed GUCs that affect the amount of
+	 *    shared memory needed have been calculated, the "shmem startup" hooks
+	 *    are called. In this stage, we allocate any shared memory, LWLocks
+	 *    and other shared resources.
+	 *
+	 * Here, in the 'neon' extension, we register just one shmem request hook
+	 * and one startup hook, which call into functions in all the subsystems
+	 * that are part of the extension. On v14, the ShmemRequest functions are
+	 * called in stage 1, and on v15 onwards they are called in stage 2.
+	 */
+
+	/* Stage 1: Define GUCs, and other early intialization */
 	pg_init_libpagestore();
+	relsize_hash_init();
 	lfc_init();
 	pg_init_walproposer();
 	init_lwlsncache();
@@ -561,6 +595,22 @@ _PG_init(void)
 
 	ReportSearchPath();
 
+	/*
+	 * Register initialization hooks for stage 2. (On v14, there's no "shmem
+	 * request" hooks, so call the ShmemRequest functions immediately.)
+	 */
+#if PG_VERSION_NUM >= 150000
+	prev_shmem_request_hook = shmem_request_hook;
+	shmem_request_hook = neon_shmem_request_hook;
+#else
+	neon_shmem_request_hook();
+#endif
+
+	/* Register hooks for stage 3 */
+	prev_shmem_startup_hook = shmem_startup_hook;
+	shmem_startup_hook = neon_shmem_startup_hook;
+
+	/* Other misc initialization */
 	prev_ExecutorStart = ExecutorStart_hook;
 	ExecutorStart_hook = neon_ExecutorStart;
 	prev_ExecutorEnd = ExecutorEnd_hook;
@@ -646,7 +696,34 @@ approximate_working_set_size(PG_FUNCTION_ARGS)
 		PG_RETURN_INT32(dc);
 }
 
-#if PG_MAJORVERSION_NUM >= 16
+/*
+ * Initialization stage 2: make requests for the amount of shared memory we
+ * will need.
+ *
+ * For a high-level explanation of the initialization process, see _PG_init().
+ */
+static void
+neon_shmem_request_hook(void)
+{
+#if PG_VERSION_NUM >= 150000
+	if (prev_shmem_request_hook)
+		prev_shmem_request_hook();
+#endif
+
+	LfcShmemRequest();
+	NeonPerfCountersShmemRequest();
+	PagestoreShmemRequest();
+	RelsizeCacheShmemRequest();
+	WalproposerShmemRequest();
+	LwLsnCacheShmemRequest();
+}
+
+
+/*
+ * Initialization stage 3: Initialize shared memory.
+ *
+ * For a high-level explanation of the initialization process, see _PG_init().
+ */
 static void
 neon_shmem_startup_hook(void)
 {
@@ -654,6 +731,15 @@ neon_shmem_startup_hook(void)
 	if (prev_shmem_startup_hook)
 		prev_shmem_startup_hook();
 
+	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
+
+	LfcShmemInit();
+	NeonPerfCountersShmemInit();
+	PagestoreShmemInit();
+	RelsizeCacheShmemInit();
+	WalproposerShmemInit();
+	LwLsnCacheShmemInit();
+
 #if PG_MAJORVERSION_NUM >= 17
 	WAIT_EVENT_NEON_LFC_MAINTENANCE = WaitEventExtensionNew("Neon/FileCache_Maintenance");
 	WAIT_EVENT_NEON_LFC_READ = WaitEventExtensionNew("Neon/FileCache_Read");
@@ -666,8 +752,9 @@ neon_shmem_startup_hook(void)
 	WAIT_EVENT_NEON_PS_READ = WaitEventExtensionNew("Neon/PS_ReadIO");
 	WAIT_EVENT_NEON_WAL_DL = WaitEventExtensionNew("Neon/WAL_Download");
 #endif
+
+	LWLockRelease(AddinShmemInitLock);
 }
-#endif
 
 /*
  * ExecutorStart hook: start up tracking if needed

pgxn/neon/neon.h

@@ -70,4 +70,19 @@ extern PGDLLEXPORT void WalProposerSync(int argc, char *argv[]);
 extern PGDLLEXPORT void WalProposerMain(Datum main_arg);
 extern PGDLLEXPORT void LogicalSlotsMonitorMain(Datum main_arg);
 
+extern void LfcShmemRequest(void);
+extern void PagestoreShmemRequest(void);
+extern void RelsizeCacheShmemRequest(void);
+extern void WalproposerShmemRequest(void);
+extern void LwLsnCacheShmemRequest(void);
+extern void NeonPerfCountersShmemRequest(void);
+
+extern void LfcShmemInit(void);
+extern void PagestoreShmemInit(void);
+extern void RelsizeCacheShmemInit(void);
+extern void WalproposerShmemInit(void);
+extern void LwLsnCacheShmemInit(void);
+extern void NeonPerfCountersShmemInit(void);
+
+
 #endif							/* NEON_H */

pgxn/neon/neon_lwlsncache.c

@@ -1,5 +1,6 @@
 #include "postgres.h"
 
+#include "neon.h"
 #include "neon_lwlsncache.h"
 
 #include "miscadmin.h"
@@ -81,14 +82,6 @@ static set_max_lwlsn_hook_type prev_set_max_lwlsn_hook = NULL;
 static set_lwlsn_relation_hook_type prev_set_lwlsn_relation_hook = NULL;
 static set_lwlsn_db_hook_type prev_set_lwlsn_db_hook = NULL;
 
-static shmem_startup_hook_type prev_shmem_startup_hook;
-
-#if PG_VERSION_NUM >= 150000
-static shmem_request_hook_type prev_shmem_request_hook;
-#endif
-
-static void shmemrequest(void);
-static void shmeminit(void);
 static void neon_set_max_lwlsn(XLogRecPtr lsn);
 
 void
@@ -99,16 +92,6 @@ init_lwlsncache(void)
 	
 	lwlc_register_gucs();
 
-	prev_shmem_startup_hook = shmem_startup_hook;
-	shmem_startup_hook = shmeminit;
-
-	#if PG_VERSION_NUM >= 150000
-	prev_shmem_request_hook = shmem_request_hook;
-	shmem_request_hook = shmemrequest;
-	#else
-	shmemrequest();
-	#endif
-	
 	prev_set_lwlsn_block_range_hook = set_lwlsn_block_range_hook;
 	set_lwlsn_block_range_hook = neon_set_lwlsn_block_range;
 	prev_set_lwlsn_block_v_hook = set_lwlsn_block_v_hook;
@@ -124,20 +107,19 @@ init_lwlsncache(void)
 }
 
 
-static void shmemrequest(void) {
+void
+LwLsnCacheShmemRequest(void)
+{
 	Size requested_size = sizeof(LwLsnCacheCtl);
-	
+
 	requested_size += hash_estimate_size(lwlsn_cache_size, sizeof(LastWrittenLsnCacheEntry));
 
 	RequestAddinShmemSpace(requested_size);
-
-	#if PG_VERSION_NUM >= 150000
-	if (prev_shmem_request_hook)
-			prev_shmem_request_hook();
-	#endif
 }
 
-static void shmeminit(void) {
+void
+LwLsnCacheShmemInit(void)
+{
 	static HASHCTL info;
 	bool found;
 	if (lwlsn_cache_size > 0)
@@ -157,9 +139,6 @@ static void shmeminit(void) {
 	}
 	dlist_init(&LwLsnCache->lastWrittenLsnLRU);
     LwLsnCache->maxLastWrittenLsn = GetRedoRecPtr();
-	if (prev_shmem_startup_hook) {
-		prev_shmem_startup_hook();
-	}
 }
 
 /*

pgxn/neon/neon_perf_counters.c

@@ -17,22 +17,32 @@
 #include "storage/shmem.h"
 #include "utils/builtins.h"
 
+#include "neon.h"
 #include "neon_perf_counters.h"
 #include "neon_pgversioncompat.h"
 
 neon_per_backend_counters *neon_per_backend_counters_shared;
 
-Size
-NeonPerfCountersShmemSize(void)
+void
+NeonPerfCountersShmemRequest(void)
 {
-	Size		size = 0;
-
-	size = add_size(size, mul_size(NUM_NEON_PERF_COUNTER_SLOTS,
-								   sizeof(neon_per_backend_counters)));
-
-	return size;
+	Size size;
+#if PG_MAJORVERSION_NUM < 15
+	/* Hack: in PG14 MaxBackends is not initialized at the time of calling NeonPerfCountersShmemRequest function.
+	 * Do it ourselves and then undo to prevent assertion failure
+	 */
+	Assert(MaxBackends == 0); /* not initialized yet */
+	InitializeMaxBackends();
+	size = mul_size(NUM_NEON_PERF_COUNTER_SLOTS, sizeof(neon_per_backend_counters));
+	MaxBackends = 0;
+#else
+	size = mul_size(NUM_NEON_PERF_COUNTER_SLOTS, sizeof(neon_per_backend_counters));
+#endif
+	RequestAddinShmemSpace(size);
 }
 
+
+
 void
 NeonPerfCountersShmemInit(void)
 {

pgxn/neon/relsize_cache.c

@@ -10,6 +10,7 @@
  */
 #include "postgres.h"
 
+#include "neon.h"
 #include "neon_pgversioncompat.h"
 
 #include "pagestore_client.h"
@@ -49,32 +50,23 @@ typedef struct
 								 * algorithm */
 } RelSizeHashControl;
 
-static HTAB *relsize_hash;
-static LWLockId relsize_lock;
-static int	relsize_hash_size;
-static RelSizeHashControl* relsize_ctl;
-static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
-#if PG_VERSION_NUM >= 150000
-static shmem_request_hook_type prev_shmem_request_hook = NULL;
-static void relsize_shmem_request(void);
-#endif
-
 /*
  * Size of a cache entry is 36 bytes. So this default will take about 2.3 MB,
  * which seems reasonable.
  */
 #define DEFAULT_RELSIZE_HASH_SIZE (64 * 1024)
 
-static void
-neon_smgr_shmem_startup(void)
+static HTAB *relsize_hash;
+static LWLockId relsize_lock;
+static int	relsize_hash_size = DEFAULT_RELSIZE_HASH_SIZE;
+static RelSizeHashControl* relsize_ctl;
+
+void
+RelsizeCacheShmemInit(void)
 {
 	static HASHCTL info;
 	bool found;
 
-	if (prev_shmem_startup_hook)
-		prev_shmem_startup_hook();
-
-	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
 	relsize_ctl = (RelSizeHashControl *) ShmemInitStruct("relsize_hash", sizeof(RelSizeHashControl), &found);
 	if (!found)
 	{
@@ -85,7 +77,6 @@ neon_smgr_shmem_startup(void)
 									 relsize_hash_size, relsize_hash_size,
 									 &info,
 									 HASH_ELEM | HASH_BLOBS);
-		LWLockRelease(AddinShmemInitLock);
 		relsize_ctl->size = 0;
 		relsize_ctl->hits = 0;
 		relsize_ctl->misses = 0;
@@ -242,34 +233,15 @@ relsize_hash_init(void)
 							PGC_POSTMASTER,
 							0,
 							NULL, NULL, NULL);
-
-	if (relsize_hash_size > 0)
-	{
-#if PG_VERSION_NUM >= 150000
-		prev_shmem_request_hook = shmem_request_hook;
-		shmem_request_hook = relsize_shmem_request;
-#else
-		RequestAddinShmemSpace(hash_estimate_size(relsize_hash_size, sizeof(RelSizeEntry)));
-		RequestNamedLWLockTranche("neon_relsize", 1);
-#endif
-
-		prev_shmem_startup_hook = shmem_startup_hook;
-		shmem_startup_hook = neon_smgr_shmem_startup;
-	}
 }
 
-#if PG_VERSION_NUM >= 150000
 /*
  * shmem_request hook: request additional shared resources.  We'll allocate or
  * attach to the shared resources in neon_smgr_shmem_startup().
  */
-static void
-relsize_shmem_request(void)
+void
+RelsizeCacheShmemRequest(void)
 {
-	if (prev_shmem_request_hook)
-		prev_shmem_request_hook();
-
 	RequestAddinShmemSpace(sizeof(RelSizeHashControl) + hash_estimate_size(relsize_hash_size, sizeof(RelSizeEntry)));
 	RequestNamedLWLockTranche("neon_relsize", 1);
 }
-#endif

pgxn/neon/walproposer_pg.c

@@ -83,10 +83,8 @@ static XLogRecPtr standby_flush_lsn = InvalidXLogRecPtr;
 static XLogRecPtr standby_apply_lsn = InvalidXLogRecPtr;
 static HotStandbyFeedback agg_hs_feedback;
 
-static void nwp_shmem_startup_hook(void);
 static void nwp_register_gucs(void);
 static void assign_neon_safekeepers(const char *newval, void *extra);
-static void nwp_prepare_shmem(void);
 static uint64 backpressure_lag_impl(void);
 static uint64 startup_backpressure_wrap(void);
 static bool backpressure_throttling_impl(void);
@@ -99,11 +97,6 @@ static TimestampTz walprop_pg_get_current_timestamp(WalProposer *wp);
 static void walprop_pg_load_libpqwalreceiver(void);
 
 static process_interrupts_callback_t PrevProcessInterruptsCallback = NULL;
-static shmem_startup_hook_type prev_shmem_startup_hook_type;
-#if PG_VERSION_NUM >= 150000
-static shmem_request_hook_type prev_shmem_request_hook = NULL;
-static void walproposer_shmem_request(void);
-#endif
 static void WalproposerShmemInit_SyncSafekeeper(void);
 
 
@@ -193,8 +186,6 @@ pg_init_walproposer(void)
 
 	nwp_register_gucs();
 
-	nwp_prepare_shmem();
-
 	delay_backend_us = &startup_backpressure_wrap;
 	PrevProcessInterruptsCallback = ProcessInterruptsCallback;
 	ProcessInterruptsCallback = backpressure_throttling_impl;
@@ -494,12 +485,11 @@ WalproposerShmemSize(void)
 	return sizeof(WalproposerShmemState);
 }
 
-static bool
+void
 WalproposerShmemInit(void)
 {
 	bool		found;
 
-	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
 	walprop_shared = ShmemInitStruct("Walproposer shared state",
 									 sizeof(WalproposerShmemState),
 									 &found);
@@ -517,9 +507,6 @@ WalproposerShmemInit(void)
 		pg_atomic_init_u64(&walprop_shared->wal_rate_limiter.last_recorded_time_us, 0);
 		/* END_HADRON */
 	}
-	LWLockRelease(AddinShmemInitLock);
-
-	return found;
 }
 
 static void
@@ -623,42 +610,15 @@ walprop_register_bgworker(void)
 
 /* shmem handling */
 
-static void
-nwp_prepare_shmem(void)
-{
-#if PG_VERSION_NUM >= 150000
-	prev_shmem_request_hook = shmem_request_hook;
-	shmem_request_hook = walproposer_shmem_request;
-#else
-	RequestAddinShmemSpace(WalproposerShmemSize());
-#endif
-	prev_shmem_startup_hook_type = shmem_startup_hook;
-	shmem_startup_hook = nwp_shmem_startup_hook;
-}
-
-#if PG_VERSION_NUM >= 150000
 /*
  * shmem_request hook: request additional shared resources.  We'll allocate or
- * attach to the shared resources in nwp_shmem_startup_hook().
+ * attach to the shared resources in WalproposerShmemInit().
  */
-static void
-walproposer_shmem_request(void)
+void
+WalproposerShmemRequest(void)
 {
-	if (prev_shmem_request_hook)
-		prev_shmem_request_hook();
-
 	RequestAddinShmemSpace(WalproposerShmemSize());
 }
-#endif
-
-static void
-nwp_shmem_startup_hook(void)
-{
-	if (prev_shmem_startup_hook_type)
-		prev_shmem_startup_hook_type();
-
-	WalproposerShmemInit();
-}
 
 WalproposerShmemState *
 GetWalpropShmemState(void)