1 files changed, 63 insertions, 1 deletions

diff --git a/innobase/trx/trx0sys.c b/innobase/trx/trx0sys.c
index d9eace5ad9a..37e148fe001 100644
--- a/innobase/trx/trx0sys.c
+++ b/innobase/trx/trx0sys.c
@@ -45,6 +45,43 @@ or there was no master log position info inside InnoDB. */
 char 		trx_sys_mysql_master_log_name[TRX_SYS_MYSQL_LOG_NAME_LEN];
 ib_longlong	trx_sys_mysql_master_log_pos	= -1;
 
+/* Do NOT merge this to the 4.1 code base! */
+ibool		trx_sys_downgrading_from_4_1_1	= FALSE;
+
+/********************************************************************
+Do NOT merge this to the 4.1 code base!
+Marks the trx sys header when we have successfully downgraded from the >= 4.1.1
+multiple tablespace format back to the 4.0 format. */
+
+void
+trx_sys_mark_downgraded_from_4_1_1(void)
+/*====================================*/
+{
+	page_t*	page;
+	byte*	doublewrite;
+	mtr_t	mtr;
+
+	/* Let us mark to the trx_sys header that the downgrade has been
+	done. */
+
+	mtr_start(&mtr);
+
+	page = buf_page_get(TRX_SYS_SPACE, TRX_SYS_PAGE_NO, RW_X_LATCH, &mtr);
+	buf_page_dbg_add_level(page, SYNC_NO_ORDER_CHECK);
+
+	doublewrite = page + TRX_SYS_DOUBLEWRITE;
+
+	mlog_write_ulint(doublewrite + TRX_SYS_DOUBLEWRITE_SPACE_ID_STORED,
+				TRX_SYS_DOUBLEWRITE_SPACE_ID_STORED_N + 1,
+				MLOG_4BYTES, &mtr);
+	mtr_commit(&mtr);
+		
+	/* Flush the modified pages to disk and make a checkpoint */
+	log_make_checkpoint_at(ut_dulint_max, TRUE);
+
+	trx_sys_downgrading_from_4_1_1 = FALSE;
+}
+
 /********************************************************************
 Determines if a page number is located inside the doublewrite buffer. */
 
@@ -187,7 +224,7 @@ start_again:
 		just read in some numbers */
 
 		trx_doublewrite_init(doublewrite);
-		
+
 		mtr_commit(&mtr);
 	} else {
 		fprintf(stderr,
@@ -351,6 +388,31 @@ trx_sys_doublewrite_init_or_restore_pages(
 					== TRX_SYS_DOUBLEWRITE_MAGIC_N) {
 		/* The doublewrite buffer has been created */
 		
+		/* Do NOT merge to the 4.1 code base! */
+        	if (mach_read_from_4(doublewrite
+				+ TRX_SYS_DOUBLEWRITE_SPACE_ID_STORED)
+            		== TRX_SYS_DOUBLEWRITE_SPACE_ID_STORED_N) {
+			
+			fprintf(stderr,
+"InnoDB: You are downgrading from the multiple tablespace format of\n"
+"InnoDB: >= MySQL-4.1.1 back to the old format of MySQL-4.0.\n"
+"InnoDB:\n"
+"InnoDB: MAKE SURE that the mysqld server is idle, and purge and the insert\n"
+"InnoDB: buffer merge have run to completion under >= 4.1.1 before trying to\n"
+"InnoDB: downgrade! You can determine this by looking at SHOW INNODB STATUS:\n"
+"InnoDB: if the Main thread is 'waiting for server activity' and SHOW\n"
+"InnoDB: PROCESSLIST shows that you have ended all other connections\n"
+"InnoDB: to mysqld, then purge and the insert buffer merge have been\n"
+"InnoDB: completed.\n"
+"InnoDB: If you have already created tables in >= 4.1.1, then those\n"
+"InnoDB: tables cannot be used under 4.0.\n"
+"InnoDB: NOTE THAT this downgrade procedure has not been properly tested!\n"
+"InnoDB: The safe way to downgrade is to dump all InnoDB tables and recreate\n"
+"InnoDB: the whole tablespace.\n");
+
+			trx_sys_downgrading_from_4_1_1 = TRUE;
+		}
+
 		trx_doublewrite_init(doublewrite);
 
 		block1 = trx_doublewrite->block1;