Remove BufFile's isTemp flag.

The isTemp flag controls whether buffile.c chops BufFile data up into
1GB segments on disk.  Since it was badly named and always true, get
rid of it.

Author: Thomas Munro (based on suggestion by Peter Geoghegan)
Reviewed-By: Peter Geoghegan, Andres Freund
Discussion: https://postgr.es/m/CAH2-Wz%3D%2B9Rfqh5UdvdW9rGezdhrMGGH-JL1X9FXXVZdeeGeOJA%40mail.gmail.com

src/backend/storage/file/buffile.c

@@ -68,7 +68,6 @@ struct BufFile
 	 * 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? */
 
@@ -99,7 +98,7 @@ static int	BufFileFlush(BufFile *file);
 
 /*
  * Create a BufFile given the first underlying physical file.
- * NOTE: caller must set isTemp and isInterXact if appropriate.
+ * NOTE: caller must set isInterXact if appropriate.
  */
 static BufFile *
 makeBufFile(File firstfile)
@@ -111,7 +110,6 @@ makeBufFile(File firstfile)
 	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;
@@ -136,7 +134,6 @@ extendBufFile(BufFile *file)
 	oldowner = CurrentResourceOwner;
 	CurrentResourceOwner = file->resowner;
 
-	Assert(file->isTemp);
 	pfile = OpenTemporaryFile(file->isInterXact);
 	Assert(pfile >= 0);
 
@@ -173,7 +170,6 @@ BufFileCreateTemp(bool interXact)
 	Assert(pfile >= 0);
 
 	file = makeBufFile(pfile);
-	file->isTemp = true;
 	file->isInterXact = interXact;
 
 	return file;
@@ -288,10 +284,12 @@ BufFileDumpBuffer(BufFile *file)
 	 */
 	while (wpos < file->nbytes)
 	{
+		off_t		availbytes;
+
 		/*
 		 * Advance to next component file if necessary and possible.
 		 */
-		if (file->curOffset >= MAX_PHYSICAL_FILESIZE && file->isTemp)
+		if (file->curOffset >= MAX_PHYSICAL_FILESIZE)
 		{
 			while (file->curFile + 1 >= file->numFiles)
 				extendBufFile(file);
@@ -304,13 +302,10 @@ BufFileDumpBuffer(BufFile *file)
 		 * write as much as asked...
 		 */
 		bytestowrite = file->nbytes - wpos;
-		if (file->isTemp)
-		{
-			off_t		availbytes = MAX_PHYSICAL_FILESIZE - file->curOffset;
+		availbytes = MAX_PHYSICAL_FILESIZE - file->curOffset;
 
-			if ((off_t) bytestowrite > availbytes)
-				bytestowrite = (int) availbytes;
-		}
+		if ((off_t) bytestowrite > availbytes)
+			bytestowrite = (int) availbytes;
 
 		/*
 		 * May need to reposition physical file.
@@ -543,20 +538,18 @@ BufFileSeek(BufFile *file, int fileno, off_t offset, int whence)
 	 * 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)
 	{
-		/* 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;
-		}
+		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;