text: /*-------------------------------------------------------------------------
   *
   * buffile.c
   *	  Management of large buffered files, primarily temporary files.
   *
   * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * IDENTIFICATION
   *	  src/backend/storage/file/buffile.c
   *
   * NOTES:
   *
   * BufFiles provide a very incomplete emulation of stdio atop virtual Files
   * (as managed by fd.c).  Currently, we only support the buffered-I/O
   * aspect of stdio: a read or write of the low-level File occurs only
   * when the buffer is filled or emptied.  This is an even bigger win
   * for virtual Files than for ordinary kernel files, since reducing the
   * frequency with which a virtual File is touched reduces "thrashing"
   * of opening/closing file descriptors.
   *
   * Note that BufFile structs are allocated with palloc(), and therefore
   * will go away automatically at transaction end.  If the underlying
   * virtual File is made with OpenTemporaryFile, then all resources for
   * the file are certain to be cleaned up even if processing is aborted
   * by ereport(ERROR).  The data structures required are made in the
   * palloc context that was current when the BufFile was created, and
   * any external resources such as temp files are owned by the ResourceOwner
   * that was current at that time.
   *
   * BufFile also supports temporary files that exceed the OS file size limit
   * (by opening multiple fd.c temporary files).  This is an essential feature
   * for sorts and hashjoins on large amounts of data.
   *-------------------------------------------------------------------------
   */
  
  #include "postgres.h"
  
  #include "executor/instrument.h"
  #include "storage/fd.h"
  #include "storage/buffile.h"
  #include "storage/buf_internals.h"
  #include "utils/resowner.h"
  
  /*
   * We break BufFiles into gigabyte-sized segments, regardless of RELSEG_SIZE.
   * The reason is that we'd like large temporary BufFiles to be spread across
   * multiple tablespaces when available.
   */
  #define MAX_PHYSICAL_FILESIZE	0x40000000
  #define BUFFILE_SEG_SIZE		(MAX_PHYSICAL_FILESIZE / BLCKSZ)
  
  /*
   * This data structure represents a buffered file that consists of one or
   * more physical files (each accessed through a virtual file descriptor
   * managed by fd.c).
   */
  struct BufFile
  {
  	int			numFiles;		/* number of physical files in set */
  	/* all files except the last have length exactly MAX_PHYSICAL_FILESIZE */
  	File	   *files;			/* palloc'd array with numFiles entries */
  	off_t	   *offsets;		/* palloc'd array with numFiles entries */
  
  	/*
  	 * offsets[i] is the current seek position of files[i].  We use this to
  	 * avoid making redundant FileSeek calls.
  	 */
  
  	bool		isTemp;			/* can only add files if this is TRUE */
  	bool		isInterXact;	/* keep open over transactions? */
  	bool		dirty;			/* does buffer need to be written? */
  
  	/*
  	 * resowner is the ResourceOwner to use for underlying temp files.  (We
  	 * don't need to remember the memory context we're using explicitly,
  	 * because after creation we only repalloc our arrays larger.)
  	 */
  	ResourceOwner resowner;
  
  	/*
  	 * "current pos" is position of start of buffer within the logical file.
  	 * Position as seen by user of BufFile is (curFile, curOffset + pos).
  	 */
  	int			curFile;		/* file index (0..n) part of current pos */
  	off_t		curOffset;		/* offset part of current pos */
  	int			pos;			/* next read/write position in buffer */
  	int			nbytes;			/* total # of valid bytes in buffer */
  	char		buffer[BLCKSZ];
  };
  
  static BufFile *makeBufFile(File firstfile);
  static void extendBufFile(BufFile *file);
  static void BufFileLoadBuffer(BufFile *file);
  static void BufFileDumpBuffer(BufFile *file);
  static int	BufFileFlush(BufFile *file);
  
  
  /*
   * Create a BufFile given the first underlying physical file.
   * NOTE: caller must set isTemp and isInterXact if appropriate.
   */
  static BufFile *
  makeBufFile(File firstfile)
  {
  	BufFile    *file = (BufFile *) palloc(sizeof(BufFile));
  
  	file->numFiles = 1;
  	file->files = (File *) palloc(sizeof(File));
  	file->files[0] = firstfile;
  	file->offsets = (off_t *) palloc(sizeof(off_t));
  	file->offsets[0] = 0L;
  	file->isTemp = false;
  	file->isInterXact = false;
  	file->dirty = false;
  	file->resowner = CurrentResourceOwner;
  	file->curFile = 0;
  	file->curOffset = 0L;
  	file->pos = 0;
  	file->nbytes = 0;
  
  	return file;
  }
  
  /*
   * Add another component temp file.
   */
  static void
  extendBufFile(BufFile *file)
  {
  	File		pfile;
  	ResourceOwner oldowner;
  
  	/* Be sure to associate the file with the BufFile's resource owner */
  	oldowner = CurrentResourceOwner;
  	CurrentResourceOwner = file->resowner;
  
  	Assert(file->isTemp);
  	pfile = OpenTemporaryFile(file->isInterXact);
  	Assert(pfile >= 0);
  
  	CurrentResourceOwner = oldowner;
  
  	file->files = (File *) repalloc(file->files,
  									(file->numFiles + 1) * sizeof(File));
  	file->offsets = (off_t *) repalloc(file->offsets,
  									   (file->numFiles + 1) * sizeof(off_t));
  	file->files[file->numFiles] = pfile;
  	file->offsets[file->numFiles] = 0L;
  	file->numFiles++;
  }
  
  /*
   * Create a BufFile for a new temporary file (which will expand to become
   * multiple temporary files if more than MAX_PHYSICAL_FILESIZE bytes are
   * written to it).
   *
   * If interXact is true, the temp file will not be automatically deleted
   * at end of transaction.
   *
   * Note: if interXact is true, the caller had better be calling us in a
   * memory context, and with a resource owner, that will survive across
   * transaction boundaries.
   */
  BufFile *
  BufFileCreateTemp(bool interXact)
  {
  	BufFile    *file;
  	File		pfile;
  
  	pfile = OpenTemporaryFile(interXact);
  	Assert(pfile >= 0);
  
  	file = makeBufFile(pfile);
  	file->isTemp = true;
  	file->isInterXact = interXact;
  
  	return file;
  }
  
  #ifdef NOT_USED
  /*
   * Create a BufFile and attach it to an already-opened virtual File.
   *
   * This is comparable to fdopen() in stdio.  This is the only way at present
   * to attach a BufFile to a non-temporary file.  Note that BufFiles created
   * in this way CANNOT be expanded into multiple files.
   */
  BufFile *
  BufFileCreate(File file)
  {
  	return makeBufFile(file);
  }
  #endif
  
  /*
   * Close a BufFile
   *
   * Like fclose(), this also implicitly FileCloses the underlying File.
   */
  void
  BufFileClose(BufFile *file)
  {
  	int			i;
  
  	/* flush any unwritten data */
  	BufFileFlush(file);
  	/* close the underlying file(s) (with delete if it's a temp file) */
  	for (i = 0; i < file->numFiles; i++)
  		FileClose(file->files[i]);
  	/* release the buffer space */
  	pfree(file->files);
  	pfree(file->offsets);
  	pfree(file);
  }
  
  /*
   * BufFileLoadBuffer
   *
   * Load some data into buffer, if possible, starting from curOffset.
   * At call, must have dirty = false, pos and nbytes = 0.
   * On exit, nbytes is number of bytes loaded.
   */
  static void
  BufFileLoadBuffer(BufFile *file)
  {
  	File		thisfile;
  
  	/*
  	 * Advance to next component file if necessary and possible.
  	 *
  	 * This path can only be taken if there is more than one component, so it
  	 * won't interfere with reading a non-temp file that is over
  	 * MAX_PHYSICAL_FILESIZE.
  	 */
  	if (file->curOffset >= MAX_PHYSICAL_FILESIZE &&
  		file->curFile + 1 < file->numFiles)
  	{
  		file->curFile++;
  		file->curOffset = 0L;
  	}
  
  	/*
  	 * May need to reposition physical file.
  	 */
  	thisfile = file->files[file->curFile];
  	if (file->curOffset != file->offsets[file->curFile])
  	{
  		if (FileSeek(thisfile, file->curOffset, SEEK_SET) != file->curOffset)
  			return;				/* seek failed, read nothing */
  		file->offsets[file->curFile] = file->curOffset;
  	}
  
  	/*
  	 * Read whatever we can get, up to a full bufferload.
  	 */
  	file->nbytes = FileRead(thisfile, file->buffer, sizeof(file->buffer));
  	if (file->nbytes < 0)
  		file->nbytes = 0;
  	file->offsets[file->curFile] += file->nbytes;
  	/* we choose not to advance curOffset here */
  
  	pgBufferUsage.temp_blks_read++;
  }
  
  /*
   * BufFileDumpBuffer
   *
   * Dump buffer contents starting at curOffset.
   * At call, should have dirty = true, nbytes > 0.
   * On exit, dirty is cleared if successful write, and curOffset is advanced.
   */
  static void
  BufFileDumpBuffer(BufFile *file)
  {
  	int			wpos = 0;
  	int			bytestowrite;
  	File		thisfile;
  
  	/*
  	 * Unlike BufFileLoadBuffer, we must dump the whole buffer even if it
  	 * crosses a component-file boundary; so we need a loop.
  	 */
  	while (wpos < file->nbytes)
  	{
  		/*
  		 * Advance to next component file if necessary and possible.
  		 */
  		if (file->curOffset >= MAX_PHYSICAL_FILESIZE && file->isTemp)
  		{
  			while (file->curFile + 1 >= file->numFiles)
  				extendBufFile(file);
  			file->curFile++;
  			file->curOffset = 0L;
  		}
  
  		/*
  		 * Enforce per-file size limit only for temp files, else just try to
  		 * write as much as asked...
  		 */
  		bytestowrite = file->nbytes - wpos;
  		if (file->isTemp)
  		{
  			off_t		availbytes = MAX_PHYSICAL_FILESIZE - file->curOffset;
  
  			if ((off_t) bytestowrite > availbytes)
  				bytestowrite = (int) availbytes;
  		}
  
  		/*
  		 * May need to reposition physical file.
  		 */
  		thisfile = file->files[file->curFile];
  		if (file->curOffset != file->offsets[file->curFile])
  		{
  			if (FileSeek(thisfile, file->curOffset, SEEK_SET) != file->curOffset)
  				return;			/* seek failed, give up */
  			file->offsets[file->curFile] = file->curOffset;
  		}
  		bytestowrite = FileWrite(thisfile, file->buffer + wpos, bytestowrite);
  		if (bytestowrite <= 0)
  			return;				/* failed to write */
  		file->offsets[file->curFile] += bytestowrite;
  		file->curOffset += bytestowrite;
  		wpos += bytestowrite;
  
  		pgBufferUsage.temp_blks_written++;
  	}
  	file->dirty = false;
  
  	/*
  	 * At this point, curOffset has been advanced to the end of the buffer,
  	 * ie, its original value + nbytes.  We need to make it point to the
  	 * logical file position, ie, original value + pos, in case that is less
  	 * (as could happen due to a small backwards seek in a dirty buffer!)
  	 */
  	file->curOffset -= (file->nbytes - file->pos);
  	if (file->curOffset < 0)	/* handle possible segment crossing */
  	{
  		file->curFile--;
  		Assert(file->curFile >= 0);
  		file->curOffset += MAX_PHYSICAL_FILESIZE;
  	}
  
  	/*
  	 * Now we can set the buffer empty without changing the logical position
  	 */
  	file->pos = 0;
  	file->nbytes = 0;
  }
  
  /*
   * BufFileRead
   *
   * Like fread() except we assume 1-byte element size.
   */
  size_t
  BufFileRead(BufFile *file, void *ptr, size_t size)
  {
  	size_t		nread = 0;
  	size_t		nthistime;
  
  	if (file->dirty)
  	{
  		if (BufFileFlush(file) != 0)
  			return 0;			/* could not flush... */
  		Assert(!file->dirty);
  	}
  
  	while (size > 0)
  	{
  		if (file->pos >= file->nbytes)
  		{
  			/* Try to load more data into buffer. */
  			file->curOffset += file->pos;
  			file->pos = 0;
  			file->nbytes = 0;
  			BufFileLoadBuffer(file);
  			if (file->nbytes <= 0)
  				break;			/* no more data available */
  		}
  
  		nthistime = file->nbytes - file->pos;
  		if (nthistime > size)
  			nthistime = size;
  		Assert(nthistime > 0);
  
  		memcpy(ptr, file->buffer + file->pos, nthistime);
  
  		file->pos += nthistime;
  		ptr = (void *) ((char *) ptr + nthistime);
  		size -= nthistime;
  		nread += nthistime;
  	}
  
  	return nread;
  }
  
  /*
   * BufFileWrite
   *
   * Like fwrite() except we assume 1-byte element size.
   */
  size_t
  BufFileWrite(BufFile *file, void *ptr, size_t size)
  {
  	size_t		nwritten = 0;
  	size_t		nthistime;
  
  	while (size > 0)
  	{
  		if (file->pos >= BLCKSZ)
  		{
  			/* Buffer full, dump it out */
  			if (file->dirty)
  			{
  				BufFileDumpBuffer(file);
  				if (file->dirty)
  					break;		/* I/O error */
  			}
  			else
  			{
  				/* Hmm, went directly from reading to writing? */
  				file->curOffset += file->pos;
  				file->pos = 0;
  				file->nbytes = 0;
  			}
  		}
  
  		nthistime = BLCKSZ - file->pos;
  		if (nthistime > size)
  			nthistime = size;
  		Assert(nthistime > 0);
  
  		memcpy(file->buffer + file->pos, ptr, nthistime);
  
  		file->dirty = true;
  		file->pos += nthistime;
  		if (file->nbytes < file->pos)
  			file->nbytes = file->pos;
  		ptr = (void *) ((char *) ptr + nthistime);
  		size -= nthistime;
  		nwritten += nthistime;
  	}
  
  	return nwritten;
  }
  
  /*
   * BufFileFlush
   *
   * Like fflush()
   */
  static int
  BufFileFlush(BufFile *file)
  {
  	if (file->dirty)
  	{
  		BufFileDumpBuffer(file);
  		if (file->dirty)
  			return EOF;
  	}
  
  	return 0;
  }
  
  /*
   * BufFileSeek
   *
   * Like fseek(), except that target position needs two values in order to
   * work when logical filesize exceeds maximum value representable by long.
   * We do not support relative seeks across more than LONG_MAX, however.
   *
   * Result is 0 if OK, EOF if not.  Logical position is not moved if an
   * impossible seek is attempted.
   */
  int
  BufFileSeek(BufFile *file, int fileno, off_t offset, int whence)
  {
  	int			newFile;
  	off_t		newOffset;
  
  	switch (whence)
  	{
  		case SEEK_SET:
  			if (fileno < 0)
  				return EOF;
  			newFile = fileno;
  			newOffset = offset;
  			break;
  		case SEEK_CUR:
  
  			/*
  			 * Relative seek considers only the signed offset, ignoring
  			 * fileno. Note that large offsets (> 1 gig) risk overflow in this
  			 * add, unless we have 64-bit off_t.
  			 */
  			newFile = file->curFile;
  			newOffset = (file->curOffset + file->pos) + offset;
  			break;
  #ifdef NOT_USED
  		case SEEK_END:
  			/* could be implemented, not needed currently */
  			break;
  #endif
  		default:
  			elog(ERROR, "invalid whence: %d", whence);
  			return EOF;
  	}
  	while (newOffset < 0)
  	{
  		if (--newFile < 0)
  			return EOF;
  		newOffset += MAX_PHYSICAL_FILESIZE;
  	}
  	if (newFile == file->curFile &&
  		newOffset >= file->curOffset &&
  		newOffset <= file->curOffset + file->nbytes)
  	{
  		/*
  		 * Seek is to a point within existing buffer; we can just adjust
  		 * pos-within-buffer, without flushing buffer.  Note this is OK
  		 * whether reading or writing, but buffer remains dirty if we were
  		 * writing.
  		 */
  		file->pos = (int) (newOffset - file->curOffset);
  		return 0;
  	}
  	/* Otherwise, must reposition buffer, so flush any dirty data */
  	if (BufFileFlush(file) != 0)
  		return EOF;
  
  	/*
  	 * At this point and no sooner, check for seek past last segment. The
  	 * above flush could have created a new segment, so checking sooner would
  	 * not work (at least not with this code).
  	 */
  	if (file->isTemp)
  	{
  		/* convert seek to "start of next seg" to "end of last seg" */
  		if (newFile == file->numFiles && newOffset == 0)
  		{
  			newFile--;
  			newOffset = MAX_PHYSICAL_FILESIZE;
  		}
  		while (newOffset > MAX_PHYSICAL_FILESIZE)
  		{
  			if (++newFile >= file->numFiles)
  				return EOF;
  			newOffset -= MAX_PHYSICAL_FILESIZE;
  		}
  	}
  	if (newFile >= file->numFiles)
  		return EOF;
  	/* Seek is OK! */
  	file->curFile = newFile;
  	file->curOffset = newOffset;
  	file->pos = 0;
  	file->nbytes = 0;
  	return 0;
  }
  
  void
  BufFileTell(BufFile *file, int *fileno, off_t *offset)
  {
  	*fileno = file->curFile;
  	*offset = file->curOffset + file->pos;
  }
  
  /*
   * BufFileSeekBlock --- block-oriented seek
   *
   * Performs absolute seek to the start of the n'th BLCKSZ-sized block of
   * the file.  Note that users of this interface will fail if their files
   * exceed BLCKSZ * LONG_MAX bytes, but that is quite a lot; we don't work
   * with tables bigger than that, either...
   *
   * Result is 0 if OK, EOF if not.  Logical position is not moved if an
   * impossible seek is attempted.
   */
  int
  BufFileSeekBlock(BufFile *file, long blknum)
  {
  	return BufFileSeek(file,
  					   (int) (blknum / BUFFILE_SEG_SIZE),
  					   (off_t) (blknum % BUFFILE_SEG_SIZE) * BLCKSZ,
  					   SEEK_SET);
  }
  
  #ifdef NOT_USED
  /*
   * BufFileTellBlock --- block-oriented tell
   *
   * Any fractional part of a block in the current seek position is ignored.
   */
  long
  BufFileTellBlock(BufFile *file)
  {
  	long		blknum;
  
  	blknum = (file->curOffset + file->pos) / BLCKSZ;
  	blknum += file->curFile * BUFFILE_SEG_SIZE;
  	return blknum;
  }
  
  #endif
  