branches/zip: Clean up after a crash during DROP INDEX.

When InnoDB crashes while dropping an index, ensure that
the index will be completely dropped during crash recovery.

row_merge_drop_index(): Before dropping an index, rename the index to
start with TEMP_INDEX_PREFIX_STR and commit the change, so that
row_merge_drop_temp_indexes() will drop the index after crash
recovery if the server crashes while dropping the index.

fseg_inode_try_get(): New function, forked from fseg_inode_get().
Return NULL if the file segment index node is free.

fseg_inode_get(): Assert that the file segment index node is not free.

fseg_free_step(): If the file segment index node is already free,
print a diagnostic message and return TRUE.

fsp_free_seg_inode(): Write a nonzero number to FSEG_MAGIC_N, so that
allocated-and-freed file segment index nodes can be better
distinguished from uninitialized ones.

This is rb://174, addressing Issue #348.

Tested by restarting mysqld upon the completion of the added
log_write_up_to() invocation below, during DROP INDEX.  The index was
dropped after crash recovery, and re-issuing the DROP INDEX did not
crash the server.

  Index: btr/btr0btr.c
  ===================================================================
  --- btr/btr0btr.c	(revision 6026)
  +++ btr/btr0btr.c	(working copy)
  @@ -42,6 +42,7 @@ Created 6/2/1994 Heikki Tuuri
   #include "ibuf0ibuf.h"
   #include "trx0trx.h"
  +#include "log0log.h"
   
   /*
   Latching strategy of the InnoDB B-tree
   --------------------------------------
  @@ -873,6 +874,8 @@ leaf_loop:
   
   		goto leaf_loop;
   	}
  +
  +	log_write_up_to(mtr.end_lsn, LOG_WAIT_ALL_GROUPS, TRUE);
   top_loop:
   	mtr_start(&mtr);

ChangeLog

+2009-10-01	The InnoDB Team
+
+	* fsp/fsp0fsp.c, row/row0merge.c:
+	Clean up after a crash during DROP INDEX.  When InnoDB crashes
+	while dropping an index, ensure that the index will be completely
+	dropped during crash recovery.  The MySQL .frm file may still
+	contain the dropped index, but there is little that we can do
+	about it.
+
 2009-09-28	The InnoDB Team
 
 	* handler/ha_innodb.cc:

fsp/fsp0fsp.c

@@ -2041,7 +2041,7 @@ fsp_free_seg_inode(
 	}
 
 	mlog_write_dulint(inode + FSEG_ID, ut_dulint_zero, mtr);
-	mlog_write_ulint(inode + FSEG_MAGIC_N, 0, MLOG_4BYTES, mtr);
+	mlog_write_ulint(inode + FSEG_MAGIC_N, 0xfa051ce3, MLOG_4BYTES, mtr);
 
 	if (ULINT_UNDEFINED
 	    == fsp_seg_inode_page_find_used(page, zip_size, mtr)) {
@@ -2057,11 +2057,11 @@ fsp_free_seg_inode(
 
 /**********************************************************************//**
 Returns the file segment inode, page x-latched.
-@return	segment inode, page x-latched */
+@return	segment inode, page x-latched; NULL if the inode is free */
 static
 fseg_inode_t*
-fseg_inode_get(
-/*===========*/
+fseg_inode_try_get(
+/*===============*/
 	fseg_header_t*	header,	/*!< in: segment header */
 	ulint		space,	/*!< in: space id */
 	ulint		zip_size,/*!< in: compressed page size in bytes
@@ -2077,8 +2077,34 @@ fseg_inode_get(
 
 	inode = fut_get_ptr(space, zip_size, inode_addr, RW_X_LATCH, mtr);
 
-	ut_ad(mach_read_from_4(inode + FSEG_MAGIC_N) == FSEG_MAGIC_N_VALUE);
+	if (UNIV_UNLIKELY
+	    (ut_dulint_is_zero(mach_read_from_8(inode + FSEG_ID)))) {
 
+		inode = NULL;
+	} else {
+		ut_ad(mach_read_from_4(inode + FSEG_MAGIC_N)
+		      == FSEG_MAGIC_N_VALUE);
+	}
+
+	return(inode);
+}
+
+/**********************************************************************//**
+Returns the file segment inode, page x-latched.
+@return	segment inode, page x-latched */
+static
+fseg_inode_t*
+fseg_inode_get(
+/*===========*/
+	fseg_header_t*	header,	/*!< in: segment header */
+	ulint		space,	/*!< in: space id */
+	ulint		zip_size,/*!< in: compressed page size in bytes
+				or 0 for uncompressed pages */
+	mtr_t*		mtr)	/*!< in: mtr handle */
+{
+	fseg_inode_t*	inode
+		= fseg_inode_try_get(header, space, zip_size, mtr);
+	ut_a(inode);
 	return(inode);
 }
 
@@ -3495,7 +3521,13 @@ fseg_free_step(
 	ut_a(descr);
 	ut_a(xdes_get_bit(descr, XDES_FREE_BIT,
 			  header_page % FSP_EXTENT_SIZE, mtr) == FALSE);
-	inode = fseg_inode_get(header, space, zip_size, mtr);
+	inode = fseg_inode_try_get(header, space, zip_size, mtr);
+
+	if (UNIV_UNLIKELY(inode == NULL)) {
+		fprintf(stderr, "double free of inode from %u:%u\n",
+			(unsigned) space, (unsigned) header_page);
+		return(TRUE);
+	}
 
 	descr = fseg_get_first_extent(inode, space, zip_size, mtr);
 

row/row0merge.c

@@ -1947,7 +1947,15 @@ row_merge_drop_index(
 	static const char str1[] =
 		"PROCEDURE DROP_INDEX_PROC () IS\n"
 		"BEGIN\n"
+		/* Rename the index, so that it will be dropped by
+		row_merge_drop_temp_indexes() at crash recovery
+		if the server crashes before this trx is committed. */
+		"UPDATE SYS_INDEXES SET NAME=CONCAT('"
+		TEMP_INDEX_PREFIX_STR "', NAME) WHERE ID = :indexid;\n"
+		"COMMIT WORK;\n"
+		/* Drop the field definitions of the index. */
 		"DELETE FROM SYS_FIELDS WHERE INDEX_ID = :indexid;\n"
+		/* Drop the index definition and the B-tree. */
 		"DELETE FROM SYS_INDEXES WHERE ID = :indexid\n"
 		"		AND TABLE_ID = :tableid;\n"
 		"END;\n";