Refactor EXEC_BACKEND code so that postmaster child processes reattach

to shared memory as soon as possible, ie, right after read_backend_variables.
The effective difference from the original code is that this happens
before instead of after read_nondefault_variables(), which loads GUC
information and is apparently capable of expanding the backend's memory
allocation more than you'd think it should.  This should fix the
failure-to-attach-to-shared-memory reports we've been seeing on Windows.
Also clean up a few bits of unnecessarily grotty EXEC_BACKEND code.

src/backend/port/sysv_shmem.c

@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/port/sysv_shmem.c,v 1.40 2004/11/09 21:30:13 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/port/sysv_shmem.c,v 1.41 2004/12/29 21:35:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -142,11 +142,7 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, uint32 size)
 	on_shmem_exit(IpcMemoryDelete, Int32GetDatum(shmid));
 
 	/* OK, should be able to attach to the segment */
-#ifdef EXEC_BACKEND
-	memAddress = shmat(shmid, UsedShmemSegAddr, PG_SHMAT_FLAGS);
-#else
 	memAddress = shmat(shmid, NULL, PG_SHMAT_FLAGS);
-#endif
 
 	if (memAddress == (void *) -1)
 		elog(FATAL, "shmat(id=%d) failed: %m", shmid);
@@ -279,7 +275,7 @@ PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
  *
  * Create a shared memory segment of the given size and initialize its
  * standard header.  Also, register an on_shmem_exit callback to release
- * the storage.  For an exec'ed backend, it just attaches.
+ * the storage.
  *
  * Dead Postgres segments are recycled if found, but we do not fail upon
  * collision with non-Postgres shmem segments.	The idea here is to detect and
@@ -303,30 +299,6 @@ PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
 	struct stat statbuf;
 #endif
 
-#ifdef EXEC_BACKEND
-	/* If Exec case, just attach and return the pointer */
-	if (UsedShmemSegAddr != NULL && !makePrivate && IsUnderPostmaster)
-	{
-		void	   *origUsedShmemSegAddr = UsedShmemSegAddr;
-
-#ifdef __CYGWIN__
-		/* cygipc (currently) appears to not detach on exec. */
-		PGSharedMemoryDetach();
-		UsedShmemSegAddr = origUsedShmemSegAddr;
-#endif
-		elog(DEBUG3, "Attaching to %p", UsedShmemSegAddr);
-		hdr = PGSharedMemoryAttach((IpcMemoryKey) UsedShmemSegID, &shmid);
-		if (hdr == NULL)
-			elog(FATAL, "could not attach to proper memory at fixed address: shmget(key=%d, addr=%p) failed: %m",
-				 (int) UsedShmemSegID, UsedShmemSegAddr);
-		if (hdr != origUsedShmemSegAddr)
-			elog(FATAL, "attaching to shared mem returned unexpected address (got %p, expected %p)",
-				 hdr, UsedShmemSegAddr);
-		UsedShmemSegAddr = hdr;
-		return hdr;
-	}
-#endif
-
 	/* Room for a header? */
 	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
 
@@ -424,6 +396,49 @@ PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
 	return hdr;
 }
 
+#ifdef EXEC_BACKEND
+
+/*
+ * PGSharedMemoryReAttach
+ *
+ * Re-attach to an already existing shared memory segment.  In the non
+ * EXEC_BACKEND case this is not used, because postmaster children inherit
+ * the shared memory segment attachment via fork().
+ *
+ * UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
+ * routine.  The caller must have already restored them to the postmaster's
+ * values.
+ */
+void
+PGSharedMemoryReAttach(void)
+{
+	IpcMemoryId shmid;
+	void	   *hdr;
+	void	   *origUsedShmemSegAddr = UsedShmemSegAddr;
+
+	Assert(UsedShmemSegAddr != NULL);
+	Assert(IsUnderPostmaster);
+
+#ifdef __CYGWIN__
+	/* cygipc (currently) appears to not detach on exec. */
+	PGSharedMemoryDetach();
+	UsedShmemSegAddr = origUsedShmemSegAddr;
+#endif
+
+	elog(DEBUG3, "Attaching to %p", UsedShmemSegAddr);
+	hdr = (void *) PGSharedMemoryAttach((IpcMemoryKey) UsedShmemSegID, &shmid);
+	if (hdr == NULL)
+		elog(FATAL, "could not reattach to shared memory (key=%d, addr=%p): %m",
+			 (int) UsedShmemSegID, UsedShmemSegAddr);
+	if (hdr != origUsedShmemSegAddr)
+		elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
+			 hdr, origUsedShmemSegAddr);
+
+	UsedShmemSegAddr = hdr;		/* probably redundant */
+}
+
+#endif /* EXEC_BACKEND */
+
 /*
  * PGSharedMemoryDetach
  *

src/backend/postmaster/postmaster.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.440 2004/11/17 08:30:09 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.441 2004/12/29 21:36:03 tgl Exp $
  *
  * NOTES
  *
@@ -1584,10 +1584,8 @@ processCancelRequest(Port *port, void *pkt)
 	int			backendPID;
 	long		cancelAuthCode;
 	Backend    *bp;
-
 #ifndef EXEC_BACKEND
 	Dlelem	   *curr;
-
 #else
 	int			i;
 #endif
@@ -3152,10 +3150,31 @@ SubPostmasterMain(int argc, char *argv[])
 
 	MyProcPid = getpid();		/* reset MyProcPid */
 
-	/* Read in file-based context */
+	/* In EXEC_BACKEND case we will not have inherited these settings */
+	IsPostmasterEnvironment = true;
+	whereToSendOutput = None;
+
+	/* Setup essential subsystems (to ensure elog() behaves sanely) */
+	MemoryContextInit();
+	InitializeGUCOptions();
+
+	/* Read in the variables file */
 	memset(&port, 0, sizeof(Port));
 	read_backend_variables(argv[2], &port);
 
+	/* Check we got appropriate args */
+	if (argc < 3)
+		elog(FATAL, "invalid subpostmaster invocation");
+
+	/*
+	 * If appropriate, physically re-attach to shared memory segment.
+	 * We want to do this before going any further to ensure that we
+	 * can attach at the same address the postmaster used.
+	 */
+	if (strcmp(argv[1], "-forkbackend") == 0 ||
+		strcmp(argv[1], "-forkboot") == 0)
+		PGSharedMemoryReAttach();
+
 	/*
 	 * Start our win32 signal implementation. This has to be done
 	 * after we read the backend variables, because we need to pick
@@ -3166,19 +3185,9 @@ SubPostmasterMain(int argc, char *argv[])
 #endif
 
 	/* In EXEC_BACKEND case we will not have inherited these settings */
-	IsPostmasterEnvironment = true;
-	whereToSendOutput = None;
 	pqinitmask();
 	PG_SETMASK(&BlockSig);
 
-	/* Setup essential subsystems */
-	MemoryContextInit();
-	InitializeGUCOptions();
-
-	/* Check we got appropriate args */
-	if (argc < 3)
-		elog(FATAL, "invalid subpostmaster invocation");
-
 	/* Read in remaining GUC variables */
 	read_nondefault_variables();
 
@@ -3187,7 +3196,7 @@ SubPostmasterMain(int argc, char *argv[])
 	{
 		/* BackendRun will close sockets */
 
-		/* Attach process to shared segments */
+		/* Attach process to shared data structures */
 		CreateSharedMemoryAndSemaphores(false, MaxBackends, 0);
 
 #ifdef USE_SSL
@@ -3208,7 +3217,7 @@ SubPostmasterMain(int argc, char *argv[])
 		/* Close the postmaster's sockets */
 		ClosePostmasterPorts(false);
 
-		/* Attach process to shared segments */
+		/* Attach process to shared data structures */
 		CreateSharedMemoryAndSemaphores(false, MaxBackends, 0);
 
 		BootstrapMain(argc - 2, argv + 2);
@@ -3259,6 +3268,7 @@ SubPostmasterMain(int argc, char *argv[])
 
 	return 1;					/* shouldn't get here */
 }
+
 #endif   /* EXEC_BACKEND */
 
 
@@ -3767,10 +3777,11 @@ read_inheritable_socket(SOCKET *dest, InheritableSocket *src)
 static void
 read_backend_variables(char *id, Port *port)
 {
+	BackendParameters param;
+
 #ifndef WIN32
 	/* Non-win32 implementation reads from file */
 	FILE *fp;
-	BackendParameters param;
 
 	/* Open file */
 	fp = AllocateFile(id, PG_BINARY_R);
@@ -3796,25 +3807,23 @@ read_backend_variables(char *id, Port *port)
 					 id, strerror(errno));
 		exit(1);
 	}
-
-	restore_backend_variables(&param, port);
 #else
 	/* Win32 version uses mapped file */
 	HANDLE paramHandle;
-	BackendParameters *param;
+	BackendParameters *paramp;
 
 	paramHandle = (HANDLE)atol(id);
-	param = MapViewOfFile(paramHandle, FILE_MAP_READ, 0, 0, 0);
-	if (!param)
+	paramp = MapViewOfFile(paramHandle, FILE_MAP_READ, 0, 0, 0);
+	if (!paramp)
 	{
 		write_stderr("could not map view of backend variables: error code %d\n",
 					 (int) GetLastError());
 		exit(1);
 	}
 
-	restore_backend_variables(param, port);
+	memcpy(&param, paramp, sizeof(BackendParameters));
 
-	if (!UnmapViewOfFile(param))
+	if (!UnmapViewOfFile(paramp))
 	{
 		write_stderr("could not unmap view of backend variables: error code %d\n",
 					 (int) GetLastError());
@@ -3828,6 +3837,8 @@ read_backend_variables(char *id, Port *port)
 		exit(1);
 	}
 #endif
+
+	restore_backend_variables(&param, port);
 }
 
 /* Restore critical backend variables from the BackendParameters struct */
@@ -3930,6 +3941,7 @@ ShmemBackendArrayRemove(pid_t pid)
 			(errmsg_internal("could not find backend entry with pid %d",
 							 (int) pid)));
 }
+
 #endif   /* EXEC_BACKEND */
 
 

src/backend/storage/file/fd.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/file/fd.c,v 1.113 2004/09/16 16:58:32 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/file/fd.c,v 1.114 2004/12/29 21:36:05 tgl Exp $
  *
  * NOTES:
  *
@@ -228,6 +228,7 @@ static File fileNameOpenFile(FileName fileName, int fileFlags, int fileMode);
 static char *filepath(const char *filename);
 static void AtProcExit_Files(int code, Datum arg);
 static void CleanupTempFiles(bool isProcExit);
+static void RemovePgTempFilesInDir(const char *tmpdirname);
 
 
 /*
@@ -1482,59 +1483,83 @@ RemovePgTempFiles(void)
 {
 	char		db_path[MAXPGPATH];
 	char		temp_path[MAXPGPATH];
-	char		rm_path[MAXPGPATH];
 	DIR		   *db_dir;
-	DIR		   *temp_dir;
 	struct dirent *db_de;
-	struct dirent *temp_de;
 
 	/*
-	 * Cycle through pg_tempfiles for all databases and remove old temp
-	 * files.
+	 * Cycle through pgsql_tmp directories for all databases and remove old
+	 * temp files.
 	 */
 	snprintf(db_path, sizeof(db_path), "%s/base", DataDir);
-	if ((db_dir = AllocateDir(db_path)) != NULL)
+	db_dir = AllocateDir(db_path);
+	if (db_dir == NULL)
 	{
-		while ((db_de = readdir(db_dir)) != NULL)
-		{
-			if (strcmp(db_de->d_name, ".") == 0
-#ifndef EXEC_BACKEND
-			/* no PG_TEMP_FILES_DIR in DataDir in non EXEC_BACKEND case */
-				|| strcmp(db_de->d_name, "..") == 0
+		/* this really should not happen */
+		elog(LOG, "could not open directory \"%s\": %m", db_path);
+		return;
+	}
+
+	while ((db_de = readdir(db_dir)) != NULL)
+	{
+		if (strcmp(db_de->d_name, ".") == 0 ||
+			strcmp(db_de->d_name, "..") == 0)
+			continue;
+
+		snprintf(temp_path, sizeof(temp_path), "%s/%s/%s",
+				 db_path, db_de->d_name, PG_TEMP_FILES_DIR);
+		RemovePgTempFilesInDir(temp_path);
+	}
+
+	FreeDir(db_dir);
+
+	/*
+	 * In EXEC_BACKEND case there is a pgsql_tmp directory at the top
+	 * level of DataDir as well.
+	 */
+#ifdef EXEC_BACKEND
+	snprintf(temp_path, sizeof(temp_path), "%s/%s",
+			 DataDir, PG_TEMP_FILES_DIR);
+	RemovePgTempFilesInDir(temp_path);
 #endif
-				)
-				continue;
-
-			snprintf(temp_path, sizeof(temp_path),
-					 "%s/%s/%s",
-					 db_path, db_de->d_name,
-					 PG_TEMP_FILES_DIR);
-			if ((temp_dir = AllocateDir(temp_path)) != NULL)
-			{
-				while ((temp_de = readdir(temp_dir)) != NULL)
-				{
-					if (strcmp(temp_de->d_name, ".") == 0 ||
-						strcmp(temp_de->d_name, "..") == 0)
-						continue;
-
-					snprintf(rm_path, sizeof(temp_path),
-							 "%s/%s/%s/%s",
-							 db_path, db_de->d_name,
-							 PG_TEMP_FILES_DIR,
-							 temp_de->d_name);
-
-					if (strncmp(temp_de->d_name,
-								PG_TEMP_FILE_PREFIX,
-								strlen(PG_TEMP_FILE_PREFIX)) == 0)
-						unlink(rm_path);
-					else
-						elog(LOG,
-							 "unexpected file found in temporary-files directory: \"%s\"",
-							 rm_path);
-				}
-				FreeDir(temp_dir);
-			}
-		}
-		FreeDir(db_dir);
+}
+
+/* Process one pgsql_tmp directory for RemovePgTempFiles */
+static void
+RemovePgTempFilesInDir(const char *tmpdirname)
+{
+	DIR		   *temp_dir;
+	struct dirent *temp_de;
+	char		rm_path[MAXPGPATH];
+
+	temp_dir = AllocateDir(tmpdirname);
+	if (temp_dir == NULL)
+	{
+		/* anything except ENOENT is fishy */
+		if (errno != ENOENT)
+			elog(LOG,
+				 "could not open temporary-files directory \"%s\": %m",
+				 tmpdirname);
+		return;
+	}
+
+	while ((temp_de = readdir(temp_dir)) != NULL)
+	{
+		if (strcmp(temp_de->d_name, ".") == 0 ||
+			strcmp(temp_de->d_name, "..") == 0)
+			continue;
+
+		snprintf(rm_path, sizeof(rm_path), "%s/%s",
+				 tmpdirname, temp_de->d_name);
+
+		if (strncmp(temp_de->d_name,
+					PG_TEMP_FILE_PREFIX,
+					strlen(PG_TEMP_FILE_PREFIX)) == 0)
+			unlink(rm_path);	/* note we ignore any error */
+		else
+			elog(LOG,
+				 "unexpected file found in temporary-files directory: \"%s\"",
+				 rm_path);
 	}
+
+	FreeDir(temp_dir);
 }

src/backend/storage/ipc/ipci.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/ipci.c,v 1.72 2004/09/29 15:15:55 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/ipci.c,v 1.73 2004/12/29 21:36:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -19,6 +19,7 @@
 #include "access/xlog.h"
 #include "miscadmin.h"
 #include "postmaster/bgwriter.h"
+#include "postmaster/postmaster.h"
 #include "storage/bufmgr.h"
 #include "storage/freespace.h"
 #include "storage/ipc.h"
@@ -37,14 +38,15 @@
  *		Creates and initializes shared memory and semaphores.
  *
  * This is called by the postmaster or by a standalone backend.
- * It is also called by a backend forked from the postmaster under
- * the EXEC_BACKEND case.  (In the non EXEC_BACKEND case, backends
- * start life already attached to shared memory.)  The initialization
- * functions are set up to simply "attach" to pre-existing shared memory
- * structures in the latter case.  We have to do that in order to
- * initialize pointers in local memory that reference the shared structures.
- * (In the non EXEC_BACKEND case, these pointer values are inherited via
- * fork() from the postmaster.)
+ * It is also called by a backend forked from the postmaster in the
+ * EXEC_BACKEND case.  In the latter case, the shared memory segment
+ * already exists and has been physically attached to, but we have to
+ * initialize pointers in local memory that reference the shared structures,
+ * because we didn't inherit the correct pointer values from the postmaster
+ * as we do in the fork() scenario.  The easiest way to do that is to run
+ * through the same code as before.  (Note that the called routines mostly
+ * check IsUnderPostmaster, rather than EXEC_BACKEND, to detect this case.
+ * This is a bit code-wasteful and could be cleaned up.)
  *
  * If "makePrivate" is true then we only need private memory, not shared
  * memory.	This is true for a standalone backend, false for a postmaster.
@@ -101,14 +103,16 @@ CreateSharedMemoryAndSemaphores(bool makePrivate,
 	else
 	{
 		/*
-		 * Attach to the shmem segment. (this should only ever be reached
-		 * by EXEC_BACKEND code, and only then with makePrivate == false)
+		 * We are reattaching to an existing shared memory segment.
+		 * This should only be reached in the EXEC_BACKEND case, and
+		 * even then only with makePrivate == false.
 		 */
 #ifdef EXEC_BACKEND
 		Assert(!makePrivate);
-		seghdr = PGSharedMemoryCreate(-1, makePrivate, 0);
+		Assert(UsedShmemSegAddr != NULL);
+		seghdr = UsedShmemSegAddr;
 #else
-		Assert(false);
+		elog(PANIC, "should be attached to shared memory already");
 #endif
 	}
 

src/include/postmaster/postmaster.h

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/postmaster/postmaster.h,v 1.7 2004/08/29 05:06:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/postmaster/postmaster.h,v 1.8 2004/12/29 21:36:08 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,6 +41,9 @@ extern void ClosePostmasterPorts(bool am_syslogger);
 #ifdef EXEC_BACKEND
 extern pid_t postmaster_forkexec(int argc, char *argv[]);
 extern int	SubPostmasterMain(int argc, char *argv[]);
+
+extern size_t ShmemBackendArraySize(void);
+extern void ShmemBackendArrayAllocation(void);
 #endif
 
 #endif   /* _POSTMASTER_H */

src/include/storage/ipc.h

@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/ipc.h,v 1.68 2004/08/29 05:06:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/ipc.h,v 1.69 2004/12/29 21:36:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -33,10 +33,4 @@ extern void CreateSharedMemoryAndSemaphores(bool makePrivate,
 								int maxBackends,
 								int port);
 
-#ifdef EXEC_BACKEND
-/* postmaster.c */
-extern size_t ShmemBackendArraySize(void);
-extern void ShmemBackendArrayAllocation(void);
-#endif
-
 #endif   /* IPC_H */

src/include/storage/pg_shmem.h

@@ -17,7 +17,7 @@
  * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/pg_shmem.h,v 1.12 2004/11/09 21:30:18 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/storage/pg_shmem.h,v 1.13 2004/12/29 21:36:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,6 +41,8 @@ typedef struct PGShmemHeader	/* standard header for all Postgres shmem */
 #ifdef EXEC_BACKEND
 extern unsigned long UsedShmemSegID;
 extern void *UsedShmemSegAddr;
+
+extern void PGSharedMemoryReAttach(void);
 #endif
 
 extern PGShmemHeader *PGSharedMemoryCreate(uint32 size, bool makePrivate,