Initialize ShmemVariableCache like other shmem areas

For sake of consistency.

Reviewed-by: Tristan Partin, Richard Guo
Discussion: https://www.postgresql.org/message-id/6537d63d-4bb5-46f8-9b5d-73a8ba4720ab@iki.fi

src/backend/access/transam/varsup.c

@@ -34,6 +34,33 @@
 VariableCache ShmemVariableCache = NULL;
 
 
+/*
+ * Initialization of shared memory for ShmemVariableCache.
+ */
+Size
+VarsupShmemSize(void)
+{
+	return sizeof(VariableCacheData);
+}
+
+void
+VarsupShmemInit(void)
+{
+	bool		found;
+
+	/* Initialize our shared state struct */
+	ShmemVariableCache = ShmemInitStruct("ShmemVariableCache",
+										 sizeof(VariableCacheData),
+										 &found);
+	if (!IsUnderPostmaster)
+	{
+		Assert(!found);
+		memset(ShmemVariableCache, 0, sizeof(VariableCacheData));
+	}
+	else
+		Assert(found);
+}
+
 /*
  * Allocate the next FullTransactionId for a new transaction or
  * subtransaction.

src/backend/postmaster/postmaster.c

@@ -89,7 +89,6 @@
 #include <pthread.h>
 #endif
 
-#include "access/transam.h"
 #include "access/xlog.h"
 #include "access/xlogrecovery.h"
 #include "catalog/pg_control.h"
@@ -513,7 +512,6 @@ typedef struct
 #endif
 	void	   *UsedShmemSegAddr;
 	slock_t    *ShmemLock;
-	VariableCache ShmemVariableCache;
 	Backend    *ShmemBackendArray;
 #ifndef HAVE_SPINLOCKS
 	PGSemaphore *SpinlockSemaArray;
@@ -6034,7 +6032,6 @@ save_backend_variables(BackendParameters *param, Port *port, BackgroundWorker *w
 	param->UsedShmemSegAddr = UsedShmemSegAddr;
 
 	param->ShmemLock = ShmemLock;
-	param->ShmemVariableCache = ShmemVariableCache;
 	param->ShmemBackendArray = ShmemBackendArray;
 
 #ifndef HAVE_SPINLOCKS
@@ -6280,7 +6277,6 @@ restore_backend_variables(BackendParameters *param, Port **port, BackgroundWorke
 	UsedShmemSegAddr = param->UsedShmemSegAddr;
 
 	ShmemLock = param->ShmemLock;
-	ShmemVariableCache = param->ShmemVariableCache;
 	ShmemBackendArray = param->ShmemBackendArray;
 
 #ifndef HAVE_SPINLOCKS

src/backend/storage/ipc/ipci.c

@@ -21,6 +21,7 @@
 #include "access/nbtree.h"
 #include "access/subtrans.h"
 #include "access/syncscan.h"
+#include "access/transam.h"
 #include "access/twophase.h"
 #include "access/xlogprefetcher.h"
 #include "access/xlogrecovery.h"
@@ -118,6 +119,7 @@ CalculateShmemSize(int *num_semaphores)
 	size = add_size(size, PredicateLockShmemSize());
 	size = add_size(size, ProcGlobalShmemSize());
 	size = add_size(size, XLogPrefetchShmemSize());
+	size = add_size(size, VarsupShmemSize());
 	size = add_size(size, XLOGShmemSize());
 	size = add_size(size, XLogRecoveryShmemSize());
 	size = add_size(size, CLOGShmemSize());
@@ -289,6 +291,7 @@ CreateOrAttachShmemStructs(void)
 	/*
 	 * Set up xlog, clog, and buffers
 	 */
+	VarsupShmemInit();
 	XLOGShmemInit();
 	XLogPrefetchShmemInit();
 	XLogRecoveryShmemInit();

src/backend/storage/ipc/shmem.c

@@ -140,14 +140,6 @@ InitShmemAllocation(void)
 	/* ShmemIndex can't be set up yet (need LWLocks first) */
 	shmhdr->index = NULL;
 	ShmemIndex = (HTAB *) NULL;
-
-	/*
-	 * Initialize ShmemVariableCache for transaction manager. (This doesn't
-	 * really belong here, but not worth moving.)
-	 */
-	ShmemVariableCache = (VariableCache)
-		ShmemAlloc(sizeof(*ShmemVariableCache));
-	memset(ShmemVariableCache, 0, sizeof(*ShmemVariableCache));
 }
 
 /*

src/include/access/transam.h

@@ -285,6 +285,8 @@ extern TransactionId TransactionIdLatest(TransactionId mainxid,
 extern XLogRecPtr TransactionIdGetCommitLSN(TransactionId xid);
 
 /* in transam/varsup.c */
+extern Size VarsupShmemSize(void);
+extern void VarsupShmemInit(void);
 extern FullTransactionId GetNewTransactionId(bool isSubXact);
 extern void AdvanceNextFullTransactionIdPastXid(TransactionId xid);
 extern FullTransactionId ReadNextFullTransactionId(void);