Esempio n. 1
0
/*
 * PGSharedMemoryCreate
 *
 * 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.
 *
 * 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
 * re-use keys that may have been assigned by a crashed postmaster or backend.
 *
 * makePrivate means to always create a new segment, rather than attach to
 * or recycle any existing segment.
 *
 * The port number is passed for possible use as a key (for SysV, we use
 * it to generate the starting shmem key).	In a standalone backend,
 * zero will be passed.
 */
PGShmemHeader *
PGSharedMemoryCreate(Size size, bool makePrivate, int port)
{
	IpcMemoryKey NextShmemSegID;
	void	   *memAddress;
	PGShmemHeader *hdr;
	IpcMemoryId shmid;
	struct stat statbuf;
	Size		sysvsize;

#if defined(EXEC_BACKEND) || !defined(MAP_HUGETLB)
	if (huge_pages == HUGE_PAGES_ON)
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("huge pages not supported on this platform")));
#endif

	/* Room for a header? */
	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));

	/*
	 * As of PostgreSQL 9.3, we normally allocate only a very small amount of
	 * System V shared memory, and only for the purposes of providing an
	 * interlock to protect the data directory.  The real shared memory block
	 * is allocated using mmap().  This works around the problem that many
	 * systems have very low limits on the amount of System V shared memory
	 * that can be allocated.  Even a limit of a few megabytes will be enough
	 * to run many copies of PostgreSQL without needing to adjust system
	 * settings.
	 *
	 * We assume that no one will attempt to run PostgreSQL 9.3 or later on
	 * systems that are ancient enough that anonymous shared memory is not
	 * supported, such as pre-2.4 versions of Linux.  If that turns out to be
	 * false, we might need to add a run-time test here and do this only if
	 * the running kernel supports it.
	 *
	 * However, we disable this logic in the EXEC_BACKEND case, and fall back
	 * to the old method of allocating the entire segment using System V
	 * shared memory, because there's no way to attach an mmap'd segment to a
	 * process after exec().  Since EXEC_BACKEND is intended only for
	 * developer use, this shouldn't be a big problem.
	 */
#ifndef EXEC_BACKEND
	AnonymousShmem = CreateAnonymousSegment(&size);
	AnonymousShmemSize = size;

	/* Now we need only allocate a minimal-sized SysV shmem block. */
	sysvsize = sizeof(PGShmemHeader);
#else
	sysvsize = size;
#endif

	/* Make sure PGSharedMemoryAttach doesn't fail without need */
	UsedShmemSegAddr = NULL;

	/* Loop till we find a free IPC key */
	NextShmemSegID = port * 1000;

	for (NextShmemSegID++;; NextShmemSegID++)
	{
		/* Try to create new segment */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
		if (memAddress)
			break;				/* successful create and attach */

		/* Check shared memory and possibly remove and recreate */

		if (makePrivate)		/* a standalone backend shouldn't do this */
			continue;

		if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, &shmid)) == NULL)
			continue;			/* can't attach, not one of mine */

		/*
		 * If I am not the creator and it belongs to an extant process,
		 * continue.
		 */
		hdr = (PGShmemHeader *) memAddress;
		if (hdr->creatorPID != getpid())
		{
			if (kill(hdr->creatorPID, 0) == 0 || errno != ESRCH)
			{
				shmdt(memAddress);
				continue;		/* segment belongs to a live process */
			}
		}

		/*
		 * The segment appears to be from a dead Postgres process, or from a
		 * previous cycle of life in this same process.  Zap it, if possible.
		 * This probably shouldn't fail, but if it does, assume the segment
		 * belongs to someone else after all, and continue quietly.
		 */
		shmdt(memAddress);
		if (shmctl(shmid, IPC_RMID, NULL) < 0)
			continue;

		/*
		 * Now try again to create the segment.
		 */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
		if (memAddress)
			break;				/* successful create and attach */

		/*
		 * Can only get here if some other process managed to create the same
		 * shmem key before we did.  Let him have that one, loop around to try
		 * next key.
		 */
	}

	/*
	 * OK, we created a new segment.  Mark it as created by this process. The
	 * order of assignments here is critical so that another Postgres process
	 * can't see the header as valid but belonging to an invalid PID!
	 */
	hdr = (PGShmemHeader *) memAddress;
	hdr->creatorPID = getpid();
	hdr->magic = PGShmemMagic;

	/* Fill in the data directory ID info, too */
	if (stat(DataDir, &statbuf) < 0)
		ereport(FATAL,
				(errcode_for_file_access(),
				 errmsg("could not stat data directory \"%s\": %m",
						DataDir)));
	hdr->device = statbuf.st_dev;
	hdr->inode = statbuf.st_ino;

	/*
	 * Initialize space allocation status for segment.
	 */
	hdr->totalsize = size;
	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));

	/* Save info for possible future use */
	UsedShmemSegAddr = memAddress;
	UsedShmemSegID = (unsigned long) NextShmemSegID;

	/*
	 * If AnonymousShmem is NULL here, then we're not using anonymous shared
	 * memory, and should return a pointer to the System V shared memory
	 * block. Otherwise, the System V shared memory block is only a shim, and
	 * we must return a pointer to the real block.
	 */
	if (AnonymousShmem == NULL)
		return hdr;
	memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
	return (PGShmemHeader *) AnonymousShmem;
}
Esempio n. 2
0
/*
 * PGSharedMemoryCreate
 *
 * 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.
 *
 * 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
 * re-use keys that may have been assigned by a crashed postmaster or backend.
 *
 * makePrivate means to always create a new segment, rather than attach to
 * or recycle any existing segment.
 *
 * The port number is passed for possible use as a key (for SysV, we use
 * it to generate the starting shmem key).  In a standalone backend,
 * zero will be passed.
 */
PGShmemHeader *
PGSharedMemoryCreate(Size size, bool makePrivate, int port,
					 PGShmemHeader **shim)
{
	IpcMemoryKey NextShmemSegID;
	void	   *memAddress;
	PGShmemHeader *hdr;
	IpcMemoryId shmid;
	struct stat statbuf;
	Size		sysvsize;

	/* Complain if hugepages demanded but we can't possibly support them */
#if !defined(USE_ANONYMOUS_SHMEM) || !defined(MAP_HUGETLB)
	if (huge_pages == HUGE_PAGES_ON)
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("huge pages not supported on this platform")));
#endif

	/* Room for a header? */
	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));

#ifdef USE_ANONYMOUS_SHMEM
	AnonymousShmem = CreateAnonymousSegment(&size);
	AnonymousShmemSize = size;

	/* Register on-exit routine to unmap the anonymous segment */
	on_shmem_exit(AnonymousShmemDetach, (Datum) 0);

	/* Now we need only allocate a minimal-sized SysV shmem block. */
	sysvsize = sizeof(PGShmemHeader);
#else
	sysvsize = size;
#endif

	/* Make sure PGSharedMemoryAttach doesn't fail without need */
	UsedShmemSegAddr = NULL;

	/* Loop till we find a free IPC key */
	NextShmemSegID = port * 1000;

	for (NextShmemSegID++;; NextShmemSegID++)
	{
		/* Try to create new segment */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
		if (memAddress)
			break;				/* successful create and attach */

		/* Check shared memory and possibly remove and recreate */

		if (makePrivate)		/* a standalone backend shouldn't do this */
			continue;

		if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, &shmid)) == NULL)
			continue;			/* can't attach, not one of mine */

		/*
		 * If I am not the creator and it belongs to an extant process,
		 * continue.
		 */
		hdr = (PGShmemHeader *) memAddress;
		if (hdr->creatorPID != getpid())
		{
			if (kill(hdr->creatorPID, 0) == 0 || errno != ESRCH)
			{
				shmdt(memAddress);
				continue;		/* segment belongs to a live process */
			}
		}

		/*
		 * The segment appears to be from a dead Postgres process, or from a
		 * previous cycle of life in this same process.  Zap it, if possible,
		 * and any associated dynamic shared memory segments, as well. This
		 * probably shouldn't fail, but if it does, assume the segment belongs
		 * to someone else after all, and continue quietly.
		 */
		if (hdr->dsm_control != 0)
			dsm_cleanup_using_control_segment(hdr->dsm_control);
		shmdt(memAddress);
		if (shmctl(shmid, IPC_RMID, NULL) < 0)
			continue;

		/*
		 * Now try again to create the segment.
		 */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
		if (memAddress)
			break;				/* successful create and attach */

		/*
		 * Can only get here if some other process managed to create the same
		 * shmem key before we did.  Let him have that one, loop around to try
		 * next key.
		 */
	}

	/*
	 * OK, we created a new segment.  Mark it as created by this process. The
	 * order of assignments here is critical so that another Postgres process
	 * can't see the header as valid but belonging to an invalid PID!
	 */
	hdr = (PGShmemHeader *) memAddress;
	hdr->creatorPID = getpid();
	hdr->magic = PGShmemMagic;
	hdr->dsm_control = 0;

	/* Fill in the data directory ID info, too */
	if (stat(DataDir, &statbuf) < 0)
		ereport(FATAL,
				(errcode_for_file_access(),
				 errmsg("could not stat data directory \"%s\": %m",
						DataDir)));
	hdr->device = statbuf.st_dev;
	hdr->inode = statbuf.st_ino;

	/*
	 * Initialize space allocation status for segment.
	 */
	hdr->totalsize = size;
	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
	*shim = hdr;

	/* Save info for possible future use */
	UsedShmemSegAddr = memAddress;
	UsedShmemSegID = (unsigned long) NextShmemSegID;

	/*
	 * If AnonymousShmem is NULL here, then we're not using anonymous shared
	 * memory, and should return a pointer to the System V shared memory
	 * block. Otherwise, the System V shared memory block is only a shim, and
	 * we must return a pointer to the real block.
	 */
#ifdef USE_ANONYMOUS_SHMEM
	if (AnonymousShmem == NULL)
		return hdr;
	memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
	return (PGShmemHeader *) AnonymousShmem;
#else
	return hdr;
#endif
}
Esempio n. 3
0
/*
 * PGSharedMemoryCreate
 *
 * 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.
 *
 * 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
 * re-use keys that may have been assigned by a crashed postmaster or backend.
 *
 * makePrivate means to always create a new segment, rather than attach to
 * or recycle any existing segment.
 *
 * The port number is passed for possible use as a key (for SysV, we use
 * it to generate the starting shmem key).	In a standalone backend,
 * zero will be passed.
 */
PGShmemHeader *
PGSharedMemoryCreate(Size size, bool makePrivate, int port)
{
	IpcMemoryKey NextShmemSegID;
	void	   *memAddress;
	PGShmemHeader *hdr;
	IpcMemoryId shmid;
	struct stat statbuf;
	Size		sysvsize = size;

	/* Room for a header? */
	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));

	/*
	 * As of PostgreSQL 9.3, we normally allocate only a very small amount of
	 * System V shared memory, and only for the purposes of providing an
	 * interlock to protect the data directory.  The real shared memory block
	 * is allocated using mmap().  This works around the problem that many
	 * systems have very low limits on the amount of System V shared memory
	 * that can be allocated.  Even a limit of a few megabytes will be enough
	 * to run many copies of PostgreSQL without needing to adjust system
	 * settings.
	 *
	 * However, we disable this logic in the EXEC_BACKEND case, and fall back
	 * to the old method of allocating the entire segment using System V shared
	 * memory, because there's no way to attach an mmap'd segment to a process
	 * after exec().  Since EXEC_BACKEND is intended only for developer use,
	 * this shouldn't be a big problem.
	 */
#ifndef EXEC_BACKEND
#ifdef SHM_HUGETLB
	/*
	 * We also only use SysV shared memoery with HugeTLB, as
	 * otherwise we need to map a file on hugetlbfs.
	 */
	if (!EnableHugeTLB)
#endif
	{
		long	pagesize = sysconf(_SC_PAGE_SIZE);

		/*
		 * Ensure request size is a multiple of pagesize.
		 *
		 * pagesize will, for practical purposes, always be a power of two.
		 * But just in case it isn't, we do it this way instead of using
		 * TYPEALIGN().
		 */
		if (pagesize > 0 && size % pagesize != 0)
			size += pagesize - (size % pagesize);

		/*
		 * We assume that no one will attempt to run PostgreSQL 9.3 or later
		 * on systems that are ancient enough that anonymous shared memory is
		 * not supported, such as pre-2.4 versions of Linux.  If that turns out
		 * to be false, we might need to add a run-time test here and do this
		 * only if the running kernel supports it.
		 */
		AnonymousShmem = mmap(NULL, size, PROT_READ|PROT_WRITE, PG_MMAP_FLAGS,
							  -1, 0);
		if (AnonymousShmem == MAP_FAILED)
			ereport(FATAL,
			 (errmsg("could not map anonymous shared memory: %m"),
			  (errno == ENOMEM) ?
			   errhint("This error usually means that PostgreSQL's request "
					   "for a shared memory segment exceeded available memory "
					   "or swap space. To reduce the request size (currently "
					   "%lu bytes), reduce PostgreSQL's shared memory usage, "
					   "perhaps by reducing shared_buffers or "
					   "max_connections.",
					   (unsigned long) size) : 0));
		AnonymousShmemSize = size;

		/* Now we need only allocate a minimal-sized SysV shmem block. */
		sysvsize = sizeof(PGShmemHeader);
	}
#endif

	/* Make sure PGSharedMemoryAttach doesn't fail without need */
	UsedShmemSegAddr = NULL;

	/* Loop till we find a free IPC key */
	NextShmemSegID = port * 1000;

	for (NextShmemSegID++;; NextShmemSegID++)
	{
		/* Try to create new segment */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
		if (memAddress)
			break;				/* successful create and attach */

		/* Check shared memory and possibly remove and recreate */

		if (makePrivate)		/* a standalone backend shouldn't do this */
			continue;

		if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, &shmid)) == NULL)
			continue;			/* can't attach, not one of mine */

		/*
		 * If I am not the creator and it belongs to an extant process,
		 * continue.
		 */
		hdr = (PGShmemHeader *) memAddress;
		if (hdr->creatorPID != getpid())
		{
			if (kill(hdr->creatorPID, 0) == 0 || errno != ESRCH)
			{
				shmdt(memAddress);
				continue;		/* segment belongs to a live process */
			}
		}

		/*
		 * The segment appears to be from a dead Postgres process, or from a
		 * previous cycle of life in this same process.  Zap it, if possible.
		 * This probably shouldn't fail, but if it does, assume the segment
		 * belongs to someone else after all, and continue quietly.
		 */
		shmdt(memAddress);
		if (shmctl(shmid, IPC_RMID, NULL) < 0)
			continue;

		/*
		 * Now try again to create the segment.
		 */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
		if (memAddress)
			break;				/* successful create and attach */

		/*
		 * Can only get here if some other process managed to create the same
		 * shmem key before we did.  Let him have that one, loop around to try
		 * next key.
		 */
	}

	/*
	 * OK, we created a new segment.  Mark it as created by this process. The
	 * order of assignments here is critical so that another Postgres process
	 * can't see the header as valid but belonging to an invalid PID!
	 */
	hdr = (PGShmemHeader *) memAddress;
	hdr->creatorPID = getpid();
	hdr->magic = PGShmemMagic;

	/* Fill in the data directory ID info, too */
	if (stat(DataDir, &statbuf) < 0)
		ereport(FATAL,
				(errcode_for_file_access(),
				 errmsg("could not stat data directory \"%s\": %m",
						DataDir)));
	hdr->device = statbuf.st_dev;
	hdr->inode = statbuf.st_ino;

	/*
	 * Initialize space allocation status for segment.
	 */
	hdr->totalsize = size;
	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));

	/* Save info for possible future use */
	UsedShmemSegAddr = memAddress;
	UsedShmemSegID = (unsigned long) NextShmemSegID;

	/*
	 * If AnonymousShmem is NULL here, then we're not using anonymous shared
	 * memory, and should return a pointer to the System V shared memory block.
	 * Otherwise, the System V shared memory block is only a shim, and we must
	 * return a pointer to the real block.
	 */
	if (AnonymousShmem == NULL)
		return hdr;
	memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
	return (PGShmemHeader *) AnonymousShmem;
}
Esempio n. 4
0
/*
 * PGSharedMemoryCreate
 *
 * 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.
 *
 * 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
 * re-use keys that may have been assigned by a crashed postmaster or backend.
 *
 * makePrivate means to always create a new segment, rather than attach to
 * or recycle any existing segment.
 *
 * The port number is passed for possible use as a key (for SysV, we use
 * it to generate the starting shmem key).	In a standalone backend,
 * zero will be passed.
 */
PGShmemHeader *
PGSharedMemoryCreate(Size size, bool makePrivate, int port)
{
	IpcMemoryKey NextShmemSegID;
	void	   *memAddress;
	PGShmemHeader *hdr;
	IpcMemoryId shmid;

#ifndef WIN32
	struct stat statbuf;
#endif

	/* Room for a header? */
	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));

	/* Make sure PGSharedMemoryAttach doesn't fail without need */
	UsedShmemSegAddr = NULL;

	/* Loop till we find a free IPC key */
	NextShmemSegID = port * 1000;

	for (NextShmemSegID++;; NextShmemSegID++)
	{
		/* Try to create new segment */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
		if (memAddress)
			break;				/* successful create and attach */

		/* Check shared memory and possibly remove and recreate */

		if (makePrivate)		/* a standalone backend shouldn't do this */
			continue;

		if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, &shmid)) == NULL)
			continue;			/* can't attach, not one of mine */

		/*
		 * If I am not the creator and it belongs to an extant process,
		 * continue.
		 */
		hdr = (PGShmemHeader *) memAddress;
		if (hdr->creatorPID != getpid())
		{
			if (kill(hdr->creatorPID, 0) == 0 || errno != ESRCH)
			{
				shmdt(memAddress);
				continue;		/* segment belongs to a live process */
			}
		}

		/*
		 * The segment appears to be from a dead Postgres process, or from a
		 * previous cycle of life in this same process.  Zap it, if possible.
		 * This probably shouldn't fail, but if it does, assume the segment
		 * belongs to someone else after all, and continue quietly.
		 */
		shmdt(memAddress);
		if (shmctl(shmid, IPC_RMID, NULL) < 0)
			continue;

		/*
		 * Now try again to create the segment.
		 */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
		if (memAddress)
			break;				/* successful create and attach */

		/*
		 * Can only get here if some other process managed to create the same
		 * shmem key before we did.  Let him have that one, loop around to try
		 * next key.
		 */
	}

	/*
	 * OK, we created a new segment.  Mark it as created by this process. The
	 * order of assignments here is critical so that another Postgres process
	 * can't see the header as valid but belonging to an invalid PID!
	 */
	hdr = (PGShmemHeader *) memAddress;
	hdr->creatorPID = getpid();
	hdr->magic = PGShmemMagic;

#ifndef WIN32
	/* Fill in the data directory ID info, too */
	if (stat(DataDir, &statbuf) < 0)
		ereport(FATAL,
				(errcode_for_file_access(),
				 errmsg("could not stat data directory \"%s\": %m",
						DataDir)));
	hdr->device = statbuf.st_dev;
	hdr->inode = statbuf.st_ino;
#endif

	/*
	 * Initialize space allocation status for segment.
	 */
	hdr->totalsize = size;
	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));

	/* Save info for possible future use */
	UsedShmemSegAddr = memAddress;
	UsedShmemSegID = (unsigned long) NextShmemSegID;

	return hdr;
}