Rewrite check for fiel sizse overflow

Author: knizhnik

src/backend/storage/file/cfs.c

@@ -470,14 +470,16 @@ int cfs_munmap(FileMap* map)
  */
 uint32 cfs_alloc_page(FileMap* map, uint32 oldSize, uint32 newSize)
 {
-	pg_atomic_fetch_add_u32(&map->hdr.usedSize, newSize - oldSize);
-	return pg_atomic_fetch_add_u32(&map->hdr.physSize, newSize);
-}
+	uint32 oldPhysSize = pg_atomic_read_u32(&map->hdr.physSize);
+	uint32 newPhysSize;
 
-void cfs_undo_alloc_page(FileMap* map, uint32 oldSize, uint32 newSize)
-{
-	pg_atomic_fetch_sub_u32(&map->hdr.usedSize, newSize - oldSize);
-	pg_atomic_fetch_sub_u32(&map->hdr.physSize, newSize);
+	do {
+		newPhysSize = oldPhysSize + newSize;
+		if (oldPhysSize > newPhysSize)
+			elog(ERROR, "CFS: segment file exceed 4Gb limit");
+	} while (!pg_atomic_compare_exchange_u32(&map->hdr.physSize, &oldPhysSize, newPhysSize));
+
+	return oldPhysSize;
 }
 
 /*

src/backend/storage/file/fd.c

@@ -1980,10 +1980,6 @@ FileWrite(File file, char *buffer, int amount)
 			 * because we want to write all updated pages sequentially
 			 */
 			pos = cfs_alloc_page(map, CFS_INODE_SIZE(inode), compressedSize);
-			if (pos > CFS_RED_LINE) {
-				cfs_undo_alloc_page(map, CFS_INODE_SIZE(inode), compressedSize);
-				elog(ERROR, "CFS: segment file exceed 4Gb limit");
-			}
 
 			inode = CFS_INODE(compressedSize, pos);
 			buffer = compressedBuffer;
@@ -2110,7 +2106,7 @@ FileWrite(File file, char *buffer, int amount)
 		{
 			elog(LOG, "CFS: backend %d forced to perform GC on file %s block %u because it's size exceed %u bytes",
 				 MyProcPid, VfdCache[file].fileName, (uint32)(VfdCache[file].seekPos / BLCKSZ),  pos);
-			cfs_gc_segment(VfdCache[file].fileName, pos + amount < CFS_YELLOW_LINE);
+			cfs_gc_segment(VfdCache[file].fileName, pos + amount < CFS_RED_LINE);
 		}
 	}
 	return returnCode;

src/include/storage/cfs.h

@@ -6,7 +6,7 @@
 #include "port/atomics.h"
 #include "storage/rijndael.h"
 
-#define CFS_VERSION "0.43"
+#define CFS_VERSION "0.45"
 
 #define CFS_GC_LOCK  0x10000000
 
@@ -52,8 +52,7 @@ typedef uint64 inode_t;
 #define CFS_INODE(size,offs)  (((inode_t)(size) << 32) | (offs))
 
 #define CFS_IMPLICIT_GC_THRESHOLD 0x80000000U /* 2Gb */
-#define CFS_YELLOW_LINE           0xC0000000U /* 3Gb */
-#define CFS_RED_LINE              0xFFF00000U /* 4Gb - page_size*100 */
+#define CFS_RED_LINE              0xC0000000U /* 3Gb */
 
 size_t cfs_compress(void* dst, size_t dst_size, void const* src, size_t src_size);
 size_t cfs_decompress(void* dst, size_t dst_size, void const* src, size_t src_size);
@@ -125,7 +124,6 @@ typedef struct
 void     cfs_lock_file(FileMap* map, char const* path);
 void     cfs_unlock_file(FileMap* map);
 uint32   cfs_alloc_page(FileMap* map, uint32 oldSize, uint32 newSize);
-void     cfs_undo_alloc_page(FileMap* map, uint32 oldSize, uint32 newSize);
 void     cfs_extend(FileMap* map, uint32 pos);
 bool     cfs_control_gc(bool enabled);
 int      cfs_msync(FileMap* map);