*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.41 1999/02/13 23:18:35 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.42 1999/04/05 22:25:11 tgl Exp $
*
*-------------------------------------------------------------------------
*/
* The magnetic disk storage manager keeps track of open file descriptors
* in its own descriptor pool. This happens for two reasons. First, at
* transaction boundaries, we walk the list of descriptors and flush
- * anything that we've dirtied in the current transaction. Second, we
- * have to support relations of > 4GBytes. In order to do this, we break
- * relations up into chunks of < 2GBytes and store one chunk in each of
- * several files that represent the relation.
+ * anything that we've dirtied in the current transaction. Second, we want
+ * to support relations larger than the OS' file size limit (often 2GBytes).
+ * In order to do that, we break relations up into chunks of < 2GBytes
+ * and store one chunk in each of several files that represent the relation.
+ * See the BLCKSZ and RELSEG_SIZE configuration constants in include/config.h.
*/
typedef struct _MdfdVec
#define MDFD_DIRTY (uint16) 0x01
#define MDFD_FREE (uint16) 0x02
-/*
- * RELSEG_SIZE appears to be the number of segments that can
- * be in a disk file. It was defined as 262144 based on 8k
- * blocks, but now that the block size can be changed, this
- * has to be calculated at compile time. Otherwise, the file
- * size limit would not work out to 2-gig (2147483648).
- *
- * The number needs to be (2 ** 31) / BLCKSZ, but to be keep
- * the math under MAXINT, pre-divide by 256 and use ...
- *
- * (((2 ** 23) / BLCKSZ) * (2 ** 8))
- *
- * 07 Jan 98 darrenk
- *
- * Now possibly let the OS handle it...
- *
- * 19 Mar 98 darrenk
- *
- */
-
-#ifndef LET_OS_MANAGE_FILESIZE
-#define RELSEG_SIZE ((8388608 / BLCKSZ) * 256)
-#endif
-
/* routines declared here */
static MdfdVec *_mdfd_openseg(Relation reln, int segno, int oflags);
static MdfdVec *_mdfd_getseg(Relation reln, int blkno, int oflag);
*/
#define BLCKSZ 8192
+/*
+ * RELSEG_SIZE is the maximum number of blocks allowed in one disk file.
+ * Thus, the maximum size of a single file is RELSEG_SIZE * BLCKSZ;
+ * relations bigger than that are divided into multiple files.
+ *
+ * CAUTION: RELSEG_SIZE * BLCKSZ must be less than your OS' limit on file size.
+ * This is typically 2Gb or 4Gb in a 32-bit operating system. By default,
+ * we make the limit one billion bytes to avoid any possible integer-overflow
+ * problems within the OS. A limit smaller than necessary only means we
+ * divide a large relation into more chunks than necessary, so it seems best
+ * to err in the direction of a small limit.
+ *
+ * CAUTION: you had best do an initdb if you change either BLCKSZ or
+ * RELSEG_SIZE.
+ */
+#define RELSEG_SIZE (1000000000 / BLCKSZ)
+
/*
* The following is set using configure.
*/