diff --git a/mysql-test/suite/innodb_plugin/r/innodb_bug56680.result b/mysql-test/suite/innodb_plugin/r/innodb_bug56680.result
new file mode 100644
index 00000000000..5e798b69167
--- /dev/null
+++ b/mysql-test/suite/innodb_plugin/r/innodb_bug56680.result
@@ -0,0 +1,109 @@
+SET GLOBAL tx_isolation='REPEATABLE-READ';
+SET GLOBAL innodb_file_format=Barracuda;
+SET GLOBAL innodb_file_per_table=on;
+CREATE TABLE bug56680(
+a INT AUTO_INCREMENT PRIMARY KEY,
+b CHAR(1),
+c INT,
+INDEX(b))
+ENGINE=InnoDB;
+INSERT INTO bug56680 VALUES(0,'x',1);
+BEGIN;
+SELECT b FROM bug56680;
+b
+x
+BEGIN;
+UPDATE bug56680 SET b='X';
+SELECT b FROM bug56680;
+b
+x
+SELECT * FROM bug56680;
+a	b	c
+1	x	1
+ROLLBACK;
+SELECT b FROM bug56680;
+b
+x
+SET GLOBAL tx_isolation='READ-UNCOMMITTED';
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+BEGIN;
+SELECT b FROM bug56680 LIMIT 2;
+b
+x
+x
+BEGIN;
+DELETE FROM bug56680 WHERE a=1;
+INSERT INTO bug56680 VALUES(1,'X',1);
+SELECT b FROM bug56680 LIMIT 3;
+b
+X
+x
+x
+SELECT b FROM bug56680 LIMIT 2;
+b
+x
+x
+CHECK TABLE bug56680;
+Table	Op	Msg_type	Msg_text
+test.bug56680	check	status	OK
+ROLLBACK;
+SELECT b FROM bug56680 LIMIT 2;
+b
+x
+x
+CHECK TABLE bug56680;
+Table	Op	Msg_type	Msg_text
+test.bug56680	check	status	OK
+SELECT b FROM bug56680 LIMIT 2;
+b
+x
+x
+CREATE TABLE bug56680_2(
+a INT AUTO_INCREMENT PRIMARY KEY,
+b VARCHAR(2) CHARSET latin1 COLLATE latin1_german2_ci,
+c INT,
+INDEX(b))
+ENGINE=InnoDB;
+INSERT INTO bug56680_2 SELECT 0,_latin1 0xdf,c FROM bug56680;
+BEGIN;
+SELECT HEX(b) FROM bug56680_2 LIMIT 2;
+HEX(b)
+DF
+DF
+DELETE FROM bug56680_2 WHERE a=1;
+INSERT INTO bug56680_2 VALUES(1,'SS',1);
+SELECT HEX(b) FROM bug56680_2 LIMIT 3;
+HEX(b)
+5353
+DF
+DF
+CHECK TABLE bug56680_2;
+Table	Op	Msg_type	Msg_text
+test.bug56680_2	check	status	OK
+ALTER TABLE bug56680_2 ROW_FORMAT=COMPRESSED KEY_BLOCK_SIZE=1;
+SELECT HEX(b) FROM bug56680_2 LIMIT 2;
+HEX(b)
+5353
+DF
+DELETE FROM bug56680_2 WHERE a=1;
+INSERT INTO bug56680_2 VALUES(1,_latin1 0xdf,1);
+SELECT HEX(b) FROM bug56680_2 LIMIT 3;
+HEX(b)
+DF
+DF
+DF
+CHECK TABLE bug56680_2;
+Table	Op	Msg_type	Msg_text
+test.bug56680_2	check	status	OK
+DROP TABLE bug56680_2;
+DROP TABLE bug56680;
diff --git a/mysql-test/suite/innodb_plugin/t/innodb_bug56680.test b/mysql-test/suite/innodb_plugin/t/innodb_bug56680.test
new file mode 100644
index 00000000000..8d0f685c723
--- /dev/null
+++ b/mysql-test/suite/innodb_plugin/t/innodb_bug56680.test
@@ -0,0 +1,142 @@
+#
+# Bug #56680 InnoDB may return wrong results from a case-insensitive index
+#
+-- source include/have_innodb_plugin.inc
+
+-- disable_query_log
+SET @tx_isolation_orig = @@tx_isolation;
+SET @innodb_file_per_table_orig = @@innodb_file_per_table;
+SET @innodb_file_format_orig = @@innodb_file_format;
+SET @innodb_file_format_check_orig = @@innodb_file_format_check;
+# The flag innodb_change_buffering_debug is only available in debug builds.
+# It instructs InnoDB to try to evict pages from the buffer pool when
+# change buffering is possible, so that the change buffer will be used
+# whenever possible.
+-- error 0,ER_UNKNOWN_SYSTEM_VARIABLE
+SET @innodb_change_buffering_debug_orig = @@innodb_change_buffering_debug;
+-- error 0,ER_UNKNOWN_SYSTEM_VARIABLE
+SET GLOBAL innodb_change_buffering_debug = 1;
+-- enable_query_log
+SET GLOBAL tx_isolation='REPEATABLE-READ';
+SET GLOBAL innodb_file_format=Barracuda;
+SET GLOBAL innodb_file_per_table=on;
+
+CREATE TABLE bug56680(
+       a INT AUTO_INCREMENT PRIMARY KEY,
+       b CHAR(1),
+       c INT,
+       INDEX(b))
+ENGINE=InnoDB;
+
+INSERT INTO bug56680 VALUES(0,'x',1);
+BEGIN;
+SELECT b FROM bug56680;
+
+connect (con1,localhost,root,,);
+connection con1;
+BEGIN;
+UPDATE bug56680 SET b='X';
+
+connection default;
+# This should return the last committed value 'x', but would return 'X'
+# due to a bug in row_search_for_mysql().
+SELECT b FROM bug56680;
+# This would always return the last committed value 'x'.
+SELECT * FROM bug56680;
+
+connection con1;
+ROLLBACK;
+disconnect con1;
+
+connection default;
+
+SELECT b FROM bug56680;
+
+# For the rest of this test, use the READ UNCOMMITTED isolation level
+# to see what exists in the secondary index.
+SET GLOBAL tx_isolation='READ-UNCOMMITTED';
+
+# Create enough rows for the table, so that the insert buffer will be
+# used for modifying the secondary index page. There must be multiple
+# index pages, because changes to the root page are never buffered.
+
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+INSERT INTO bug56680 SELECT 0,b,c FROM bug56680;
+
+BEGIN;
+SELECT b FROM bug56680 LIMIT 2;
+
+connect (con1,localhost,root,,);
+connection con1;
+BEGIN;
+DELETE FROM bug56680 WHERE a=1;
+# This should be buffered, if innodb_change_buffering_debug = 1 is in effect.
+INSERT INTO bug56680 VALUES(1,'X',1);
+
+# This should force an insert buffer merge, and return 'X' in the first row.
+SELECT b FROM bug56680 LIMIT 3;
+
+connection default;
+SELECT b FROM bug56680 LIMIT 2;
+CHECK TABLE bug56680;
+
+connection con1;
+ROLLBACK;
+SELECT b FROM bug56680 LIMIT 2;
+CHECK TABLE bug56680;
+
+connection default;
+disconnect con1;
+
+SELECT b FROM bug56680 LIMIT 2;
+
+CREATE TABLE bug56680_2(
+       a INT AUTO_INCREMENT PRIMARY KEY,
+       b VARCHAR(2) CHARSET latin1 COLLATE latin1_german2_ci,
+       c INT,
+       INDEX(b))
+ENGINE=InnoDB;
+
+INSERT INTO bug56680_2 SELECT 0,_latin1 0xdf,c FROM bug56680;
+
+BEGIN;
+SELECT HEX(b) FROM bug56680_2 LIMIT 2;
+DELETE FROM bug56680_2 WHERE a=1;
+# This should be buffered, if innodb_change_buffering_debug = 1 is in effect.
+INSERT INTO bug56680_2 VALUES(1,'SS',1);
+
+# This should force an insert buffer merge, and return 'SS' in the first row.
+SELECT HEX(b) FROM bug56680_2 LIMIT 3;
+CHECK TABLE bug56680_2;
+
+# Test this with compressed tables.
+ALTER TABLE bug56680_2 ROW_FORMAT=COMPRESSED KEY_BLOCK_SIZE=1;
+
+SELECT HEX(b) FROM bug56680_2 LIMIT 2;
+DELETE FROM bug56680_2 WHERE a=1;
+# This should be buffered, if innodb_change_buffering_debug = 1 is in effect.
+INSERT INTO bug56680_2 VALUES(1,_latin1 0xdf,1);
+
+# This should force an insert buffer merge, and return 0xdf in the first row.
+SELECT HEX(b) FROM bug56680_2 LIMIT 3;
+CHECK TABLE bug56680_2;
+
+DROP TABLE bug56680_2;
+DROP TABLE bug56680;
+
+-- disable_query_log
+SET GLOBAL tx_isolation = @tx_isolation_orig;
+SET GLOBAL innodb_file_per_table = @innodb_file_per_table_orig;
+SET GLOBAL innodb_file_format = @innodb_file_format_orig;
+SET GLOBAL innodb_file_format_check = @innodb_file_format_check_orig;
+-- error 0, ER_UNKNOWN_SYSTEM_VARIABLE
+SET GLOBAL innodb_change_buffering_debug = @innodb_change_buffering_debug_orig;
diff --git a/storage/innodb_plugin/ChangeLog b/storage/innodb_plugin/ChangeLog
index 488669346fd..db37fa2b4bb 100644
--- a/storage/innodb_plugin/ChangeLog
+++ b/storage/innodb_plugin/ChangeLog
@@ -1,3 +1,13 @@
+2010-10-19	The InnoDB Team
+
+	* btr/btr0cur.c, buf/buf0buf.c, buf/buf0flu.c, handler/ha_innodb.cc,
+	ibuf/ibuf0ibuf.c, include/btr0cur.h, include/buf0flu.h,
+	include/ibuf0ibuf.h, include/row0mysql.h,
+	row/row0mysql.c, row/row0sel.c,
+	innodb_bug56680.test, innodb_bug56680.result:
+	Fix Bug #56680 InnoDB may return wrong results from a
+	case-insensitive covering index
+
 2010-10-18	The InnoDB Team
 
 	* handler/ha_innodb.cc, handler/ha_innodb.h, innodb_bug57252.result,
diff --git a/storage/innodb_plugin/btr/btr0cur.c b/storage/innodb_plugin/btr/btr0cur.c
index 9812e91e8a5..79fe328a631 100644
--- a/storage/innodb_plugin/btr/btr0cur.c
+++ b/storage/innodb_plugin/btr/btr0cur.c
@@ -1626,7 +1626,7 @@ func_exit:
 See if there is enough place in the page modification log to log
 an update-in-place.
 @return	TRUE if enough place */
-static
+UNIV_INTERN
 ibool
 btr_cur_update_alloc_zip(
 /*=====================*/
diff --git a/storage/innodb_plugin/buf/buf0buf.c b/storage/innodb_plugin/buf/buf0buf.c
index 660686bac1e..65d4311b840 100644
--- a/storage/innodb_plugin/buf/buf0buf.c
+++ b/storage/innodb_plugin/buf/buf0buf.c
@@ -2286,6 +2286,30 @@ wait_until_unfixed:
 	bytes. */
 	UNIV_MEM_ASSERT_RW(&block->page, sizeof block->page);
 #endif
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+	if (mode == BUF_GET_IF_IN_POOL && ibuf_debug) {
+		/* Try to evict the block from the buffer pool, to use the
+		insert buffer as much as possible. */
+
+		if (buf_LRU_free_block(&block->page, TRUE, NULL)
+		    == BUF_LRU_FREED) {
+			buf_pool_mutex_exit();
+			mutex_exit(&block->mutex);
+			fprintf(stderr,
+				"innodb_change_buffering_debug evict %u %u\n",
+				(unsigned) space, (unsigned) offset);
+			return(NULL);
+		} else if (buf_flush_page_try(block)) {
+			fprintf(stderr,
+				"innodb_change_buffering_debug flush %u %u\n",
+				(unsigned) space, (unsigned) offset);
+			guess = block;
+			goto loop;
+		}
+
+		/* Failed to evict the page; change it directly */
+	}
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
 
 	buf_block_buf_fix_inc(block, file, line);
 
diff --git a/storage/innodb_plugin/buf/buf0flu.c b/storage/innodb_plugin/buf/buf0flu.c
index 747ce65879d..2123f8a060d 100644
--- a/storage/innodb_plugin/buf/buf0flu.c
+++ b/storage/innodb_plugin/buf/buf0flu.c
@@ -1039,6 +1039,82 @@ buf_flush_write_block_low(
 	}
 }
 
+# if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+/********************************************************************//**
+Writes a flushable page asynchronously from the buffer pool to a file.
+NOTE: buf_pool_mutex and block->mutex must be held upon entering this
+function, and they will be released by this function after flushing.
+This is loosely based on buf_flush_batch() and buf_flush_page().
+@return TRUE if the page was flushed and the mutexes released */
+UNIV_INTERN
+ibool
+buf_flush_page_try(
+/*===============*/
+	buf_block_t*	block)		/*!< in/out: buffer control block */
+{
+	ut_ad(buf_pool_mutex_own());
+	ut_ad(buf_block_get_state(block) == BUF_BLOCK_FILE_PAGE);
+	ut_ad(mutex_own(&block->mutex));
+
+	if (!buf_flush_ready_for_flush(&block->page, BUF_FLUSH_LRU)) {
+		return(FALSE);
+	}
+
+	if (buf_pool->n_flush[BUF_FLUSH_LRU] > 0
+	    || buf_pool->init_flush[BUF_FLUSH_LRU]) {
+		/* There is already a flush batch of the same type running */
+		return(FALSE);
+	}
+
+	buf_pool->init_flush[BUF_FLUSH_LRU] = TRUE;
+
+	buf_page_set_io_fix(&block->page, BUF_IO_WRITE);
+
+	buf_page_set_flush_type(&block->page, BUF_FLUSH_LRU);
+
+	if (buf_pool->n_flush[BUF_FLUSH_LRU]++ == 0) {
+
+		os_event_reset(buf_pool->no_flush[BUF_FLUSH_LRU]);
+	}
+
+	/* VERY IMPORTANT:
+	Because any thread may call the LRU flush, even when owning
+	locks on pages, to avoid deadlocks, we must make sure that the
+	s-lock is acquired on the page without waiting: this is
+	accomplished because buf_flush_ready_for_flush() must hold,
+	and that requires the page not to be bufferfixed. */
+
+	rw_lock_s_lock_gen(&block->lock, BUF_IO_WRITE);
+
+	/* Note that the s-latch is acquired before releasing the
+	buf_pool mutex: this ensures that the latch is acquired
+	immediately. */
+
+	mutex_exit(&block->mutex);
+	buf_pool_mutex_exit();
+
+	/* Even though block is not protected by any mutex at this
+	point, it is safe to access block, because it is io_fixed and
+	oldest_modification != 0.  Thus, it cannot be relocated in the
+	buffer pool or removed from flush_list or LRU_list. */
+
+	buf_flush_write_block_low(&block->page);
+
+	buf_pool_mutex_enter();
+	buf_pool->init_flush[BUF_FLUSH_LRU] = FALSE;
+
+	if (buf_pool->n_flush[BUF_FLUSH_LRU] == 0) {
+		/* The running flush batch has ended */
+		os_event_set(buf_pool->no_flush[BUF_FLUSH_LRU]);
+	}
+
+	buf_pool_mutex_exit();
+	buf_flush_buffered_writes();
+
+	return(TRUE);
+}
+# endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
 /********************************************************************//**
 Writes a flushable page asynchronously from the buffer pool to a file.
 NOTE: in simulated aio we must call
diff --git a/storage/innodb_plugin/handler/ha_innodb.cc b/storage/innodb_plugin/handler/ha_innodb.cc
index 35f1a4974e2..99d4f294f81 100644
--- a/storage/innodb_plugin/handler/ha_innodb.cc
+++ b/storage/innodb_plugin/handler/ha_innodb.cc
@@ -4432,17 +4432,18 @@ include_field:
 		n_requested_fields++;
 
 		templ->col_no = i;
+		templ->clust_rec_field_no = dict_col_get_clust_pos(
+			&index->table->cols[i], clust_index);
+		ut_ad(templ->clust_rec_field_no != ULINT_UNDEFINED);
 
 		if (index == clust_index) {
-			templ->rec_field_no = dict_col_get_clust_pos(
-				&index->table->cols[i], index);
+			templ->rec_field_no = templ->clust_rec_field_no;
 		} else {
 			templ->rec_field_no = dict_index_get_nth_col_pos(
 								index, i);
-		}
-
-		if (templ->rec_field_no == ULINT_UNDEFINED) {
-			prebuilt->need_to_access_clustered = TRUE;
+			if (templ->rec_field_no == ULINT_UNDEFINED) {
+				prebuilt->need_to_access_clustered = TRUE;
+			}
 		}
 
 		if (field->null_ptr) {
@@ -4494,9 +4495,7 @@ skip_field:
 		for (i = 0; i < n_requested_fields; i++) {
 			templ = prebuilt->mysql_template + i;
 
-			templ->rec_field_no = dict_col_get_clust_pos(
-				&index->table->cols[templ->col_no],
-				clust_index);
+			templ->rec_field_no = templ->clust_rec_field_no;
 		}
 	}
 }
@@ -10945,6 +10944,13 @@ static MYSQL_SYSVAR_STR(change_buffering, innobase_change_buffering,
   innodb_change_buffering_validate,
   innodb_change_buffering_update, "inserts"); 
 
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+static MYSQL_SYSVAR_UINT(change_buffering_debug, ibuf_debug,
+  PLUGIN_VAR_RQCMDARG,
+  "Debug flags for InnoDB change buffering (0=none)",
+  NULL, NULL, 0, 0, 1, 0);
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
 static MYSQL_SYSVAR_ULONG(read_ahead_threshold, srv_read_ahead_threshold,
   PLUGIN_VAR_RQCMDARG,
   "Number of pages that must be accessed sequentially for InnoDB to "
@@ -11005,6 +11011,9 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(version),
   MYSQL_SYSVAR(use_sys_malloc),
   MYSQL_SYSVAR(change_buffering),
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+  MYSQL_SYSVAR(change_buffering_debug),
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
   MYSQL_SYSVAR(read_ahead_threshold),
   MYSQL_SYSVAR(io_capacity),
   NULL
diff --git a/storage/innodb_plugin/ibuf/ibuf0ibuf.c b/storage/innodb_plugin/ibuf/ibuf0ibuf.c
index 5e9b4b27611..701e8f0ef04 100644
--- a/storage/innodb_plugin/ibuf/ibuf0ibuf.c
+++ b/storage/innodb_plugin/ibuf/ibuf0ibuf.c
@@ -49,6 +49,7 @@ Created 7/19/1997 Heikki Tuuri
 #include "btr0cur.h"
 #include "btr0pcur.h"
 #include "btr0btr.h"
+#include "row0upd.h"
 #include "sync0sync.h"
 #include "dict0boot.h"
 #include "fut0lst.h"
@@ -170,6 +171,11 @@ access order rules. */
 /** Operations that can currently be buffered. */
 UNIV_INTERN ibuf_use_t	ibuf_use		= IBUF_USE_INSERT;
 
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+/** Flag to control insert buffer debugging. */
+UNIV_INTERN uint	ibuf_debug;
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
 /** The insert buffer control structure */
 UNIV_INTERN ibuf_t*	ibuf			= NULL;
 
@@ -2881,9 +2887,80 @@ During merge, inserts to an index page a secondary index entry extracted
 from the insert buffer. */
 static
 void
+ibuf_insert_to_index_page_low(
+/*==========================*/
+	const dtuple_t*	entry,	/*!< in: buffered entry to insert */
+	buf_block_t*	block,	/*!< in/out: index page where the buffered
+				entry should be placed */
+	dict_index_t*	index,	/*!< in: record descriptor */
+	mtr_t*		mtr,	/*!< in/out: mtr */
+	page_cur_t*	page_cur)/*!< in/out: cursor positioned on the record
+				after which to insert the buffered entry */
+{
+	const page_t*	page;
+	ulint		space;
+	ulint		page_no;
+	ulint		zip_size;
+	const page_t*	bitmap_page;
+	ulint		old_bits;
+
+	if (UNIV_LIKELY
+	    (page_cur_tuple_insert(page_cur, entry, index, 0, mtr) != NULL)) {
+		return;
+	}
+
+	/* If the record did not fit, reorganize */
+
+	btr_page_reorganize(block, index, mtr);
+	page_cur_search(block, index, entry, PAGE_CUR_LE, page_cur);
+
+	/* This time the record must fit */
+
+	if (UNIV_LIKELY
+	    (page_cur_tuple_insert(page_cur, entry, index, 0, mtr) != NULL)) {
+		return;
+	}
+
+	page = buf_block_get_frame(block);
+
+	ut_print_timestamp(stderr);
+
+	fprintf(stderr,
+		"  InnoDB: Error: Insert buffer insert fails;"
+		" page free %lu, dtuple size %lu\n",
+		(ulong) page_get_max_insert_size(page, 1),
+		(ulong) rec_get_converted_size(index, entry, 0));
+	fputs("InnoDB: Cannot insert index record ", stderr);
+	dtuple_print(stderr, entry);
+	fputs("\nInnoDB: The table where this index record belongs\n"
+	      "InnoDB: is now probably corrupt. Please run CHECK TABLE on\n"
+	      "InnoDB: that table.\n", stderr);
+
+	space = page_get_space_id(page);
+	zip_size = buf_block_get_zip_size(block);
+	page_no = page_get_page_no(page);
+
+	bitmap_page = ibuf_bitmap_get_map_page(space, page_no, zip_size, mtr);
+	old_bits = ibuf_bitmap_page_get_bits(bitmap_page, page_no, zip_size,
+					     IBUF_BITMAP_FREE, mtr);
+
+	fprintf(stderr,
+		"InnoDB: space %lu, page %lu, zip_size %lu, bitmap bits %lu\n",
+		(ulong) space, (ulong) page_no,
+		(ulong) zip_size, (ulong) old_bits);
+
+	fputs("InnoDB: Submit a detailed bug report"
+	      " to http://bugs.mysql.com\n", stderr);
+}
+
+/************************************************************************
+During merge, inserts to an index page a secondary index entry extracted
+from the insert buffer. */
+static
+void
 ibuf_insert_to_index_page(
 /*======================*/
-	dtuple_t*	entry,	/*!< in: buffered entry to insert */
+	const dtuple_t*	entry,	/*!< in: buffered entry to insert */
 	buf_block_t*	block,	/*!< in/out: index page where the buffered entry
 				should be placed */
 	dict_index_t*	index,	/*!< in: record descriptor */
@@ -2893,11 +2970,10 @@ ibuf_insert_to_index_page(
 	ulint		low_match;
 	page_t*		page		= buf_block_get_frame(block);
 	rec_t*		rec;
-	page_t*		bitmap_page;
-	ulint		old_bits;
 
 	ut_ad(ibuf_inside());
 	ut_ad(dtuple_check_typed(entry));
+	ut_ad(!buf_block_align(page)->is_hashed);
 
 	if (UNIV_UNLIKELY(dict_table_is_comp(index->table)
 			  != (ibool)!!page_is_comp(page))) {
@@ -2935,71 +3011,86 @@ dump:
 	low_match = page_cur_search(block, index, entry,
 				    PAGE_CUR_LE, &page_cur);
 
-	if (low_match == dtuple_get_n_fields(entry)) {
+	if (UNIV_UNLIKELY(low_match == dtuple_get_n_fields(entry))) {
+		mem_heap_t*	heap;
+		upd_t*		update;
+		ulint*		offsets;
 		page_zip_des_t*	page_zip;
 
 		rec = page_cur_get_rec(&page_cur);
+
+		/* This is based on
+		row_ins_sec_index_entry_by_modify(BTR_MODIFY_LEAF). */
+		ut_ad(rec_get_deleted_flag(rec, page_is_comp(page)));
+
+		heap = mem_heap_create(1024);
+
+		offsets = rec_get_offsets(rec, index, NULL, ULINT_UNDEFINED,
+					  &heap);
+		update = row_upd_build_sec_rec_difference_binary(
+			index, entry, rec, NULL, heap);
+
 		page_zip = buf_block_get_page_zip(block);
 
-		btr_cur_del_unmark_for_ibuf(rec, page_zip, mtr);
-	} else {
-		rec = page_cur_tuple_insert(&page_cur, entry, index, 0, mtr);
-
-		if (UNIV_LIKELY(rec != NULL)) {
+		if (update->n_fields == 0) {
+			/* The records only differ in the delete-mark.
+			Clear the delete-mark, like we did before
+			Bug #56680 was fixed. */
+			btr_cur_del_unmark_for_ibuf(rec, page_zip, mtr);
+updated_in_place:
+			mem_heap_free(heap);
 			return;
 		}
 
-		/* If the record did not fit, reorganize */
+		/* Copy the info bits. Clear the delete-mark. */
+		update->info_bits = rec_get_info_bits(rec, page_is_comp(page));
+		update->info_bits &= ~REC_INFO_DELETED_FLAG;
 
-		btr_page_reorganize(block, index, mtr);
-		page_cur_search(block, index, entry, PAGE_CUR_LE, &page_cur);
-
-		/* This time the record must fit */
-		if (UNIV_UNLIKELY
-		    (!page_cur_tuple_insert(&page_cur, entry, index,
-					    0, mtr))) {
-			ulint	space;
-			ulint	page_no;
-			ulint	zip_size;
-
-			ut_print_timestamp(stderr);
-
-			fprintf(stderr,
-				"  InnoDB: Error: Insert buffer insert"
-				" fails; page free %lu,"
-				" dtuple size %lu\n",
-				(ulong) page_get_max_insert_size(
-					page, 1),
-				(ulong) rec_get_converted_size(
-					index, entry, 0));
-			fputs("InnoDB: Cannot insert index record ",
-			      stderr);
-			dtuple_print(stderr, entry);
-			fputs("\nInnoDB: The table where"
-			      " this index record belongs\n"
-			      "InnoDB: is now probably corrupt."
-			      " Please run CHECK TABLE on\n"
-			      "InnoDB: that table.\n", stderr);
-
-			space = page_get_space_id(page);
-			zip_size = buf_block_get_zip_size(block);
-			page_no = page_get_page_no(page);
-
-			bitmap_page = ibuf_bitmap_get_map_page(
-				space, page_no, zip_size, mtr);
-			old_bits = ibuf_bitmap_page_get_bits(
-				bitmap_page, page_no, zip_size,
-				IBUF_BITMAP_FREE, mtr);
-
-			fprintf(stderr,
-				"InnoDB: space %lu, page %lu,"
-				" zip_size %lu, bitmap bits %lu\n",
-				(ulong) space, (ulong) page_no,
-				(ulong) zip_size, (ulong) old_bits);
-
-			fputs("InnoDB: Submit a detailed bug report"
-			      " to http://bugs.mysql.com\n", stderr);
+		/* We cannot invoke btr_cur_optimistic_update() here,
+		because we do not have a btr_cur_t or que_thr_t,
+		as the insert buffer merge occurs at a very low level. */
+		if (!row_upd_changes_field_size_or_external(index, offsets,
+							    update)
+		    && (!page_zip || btr_cur_update_alloc_zip(
+				page_zip, block, index,
+				rec_offs_size(offsets), FALSE, mtr))) {
+			/* This is the easy case. Do something similar
+			to btr_cur_update_in_place(). */
+			row_upd_rec_in_place(rec, index, offsets,
+					     update, page_zip);
+			goto updated_in_place;
 		}
+
+		/* A collation may identify values that differ in
+		storage length.
+		Some examples (1 or 2 bytes):
+		utf8_turkish_ci: I = U+0131 LATIN SMALL LETTER DOTLESS I
+		utf8_general_ci: S = U+00DF LATIN SMALL LETTER SHARP S
+		utf8_general_ci: A = U+00E4 LATIN SMALL LETTER A WITH DIAERESIS
+
+		latin1_german2_ci: SS = U+00DF LATIN SMALL LETTER SHARP S
+
+		Examples of a character (3-byte UTF-8 sequence)
+		identified with 2 or 4 characters (1-byte UTF-8 sequences):
+
+		utf8_unicode_ci: 'II' = U+2171 SMALL ROMAN NUMERAL TWO
+		utf8_unicode_ci: '(10)' = U+247D PARENTHESIZED NUMBER TEN
+		*/
+
+		/* Delete the different-length record, and insert the
+		buffered one. */
+
+		lock_rec_store_on_page_infimum(block, rec);
+		page_cur_delete_rec(&page_cur, index, offsets, mtr);
+		page_cur_move_to_prev(&page_cur);
+		mem_heap_free(heap);
+
+		ibuf_insert_to_index_page_low(entry, block, index, mtr,
+					      &page_cur);
+		lock_rec_restore_from_page_infimum(block, rec, block);
+	} else {
+		ibuf_insert_to_index_page_low(entry, block, index, mtr,
+					      &page_cur);
 	}
 }
 
diff --git a/storage/innodb_plugin/include/btr0cur.h b/storage/innodb_plugin/include/btr0cur.h
index e151fdcb563..7f6bff11f84 100644
--- a/storage/innodb_plugin/include/btr0cur.h
+++ b/storage/innodb_plugin/include/btr0cur.h
@@ -242,6 +242,22 @@ btr_cur_pessimistic_insert(
 	que_thr_t*	thr,	/*!< in: query thread or NULL */
 	mtr_t*		mtr);	/*!< in: mtr */
 /*************************************************************//**
+See if there is enough place in the page modification log to log
+an update-in-place.
+@return	TRUE if enough place */
+UNIV_INTERN
+ibool
+btr_cur_update_alloc_zip(
+/*=====================*/
+	page_zip_des_t*	page_zip,/*!< in/out: compressed page */
+	buf_block_t*	block,	/*!< in/out: buffer page */
+	dict_index_t*	index,	/*!< in: the index corresponding to the block */
+	ulint		length,	/*!< in: size needed */
+	ibool		create,	/*!< in: TRUE=delete-and-insert,
+				FALSE=update-in-place */
+	mtr_t*		mtr)	/*!< in: mini-transaction */
+	__attribute__((nonnull, warn_unused_result));
+/*************************************************************//**
 Updates a record when the update causes no size changes in its fields.
 @return	DB_SUCCESS or error number */
 UNIV_INTERN
diff --git a/storage/innodb_plugin/include/buf0flu.h b/storage/innodb_plugin/include/buf0flu.h
index c996f6eaab4..cb8c49fde15 100644
--- a/storage/innodb_plugin/include/buf0flu.h
+++ b/storage/innodb_plugin/include/buf0flu.h
@@ -75,6 +75,20 @@ buf_flush_init_for_writing(
 	ib_uint64_t	newest_lsn);	/*!< in: newest modification lsn
 					to the page */
 #ifndef UNIV_HOTBACKUP
+# if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+/********************************************************************//**
+Writes a flushable page asynchronously from the buffer pool to a file.
+NOTE: buf_pool_mutex and block->mutex must be held upon entering this
+function, and they will be released by this function after flushing.
+This is loosely based on buf_flush_batch() and buf_flush_page().
+@return TRUE if the page was flushed and the mutexes released */
+UNIV_INTERN
+ibool
+buf_flush_page_try(
+/*===============*/
+	buf_block_t*	block)		/*!< in/out: buffer control block */
+	__attribute__((nonnull, warn_unused_result));
+# endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
 /*******************************************************************//**
 This utility flushes dirty blocks from the end of the LRU list or flush_list.
 NOTE 1: in the case of an LRU flush the calling thread may own latches to
diff --git a/storage/innodb_plugin/include/ibuf0ibuf.h b/storage/innodb_plugin/include/ibuf0ibuf.h
index 8aa21fb9d95..f8cc4471d43 100644
--- a/storage/innodb_plugin/include/ibuf0ibuf.h
+++ b/storage/innodb_plugin/include/ibuf0ibuf.h
@@ -48,6 +48,11 @@ typedef enum {
 /** Operations that can currently be buffered. */
 extern ibuf_use_t	ibuf_use;
 
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+/** Flag to control insert buffer debugging. */
+extern uint		ibuf_debug;
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
 /** The insert buffer control structure */
 extern ibuf_t*		ibuf;
 
diff --git a/storage/innodb_plugin/include/row0mysql.h b/storage/innodb_plugin/include/row0mysql.h
index b69e657361b..42182cc0044 100644
--- a/storage/innodb_plugin/include/row0mysql.h
+++ b/storage/innodb_plugin/include/row0mysql.h
@@ -527,6 +527,10 @@ struct mysql_row_templ_struct {
 					Innobase record in the current index;
 					not defined if template_type is
 					ROW_MYSQL_WHOLE_ROW */
+	ulint	clust_rec_field_no;	/*!< field number of the column in an
+					Innobase record in the clustered index;
+					not defined if template_type is
+					ROW_MYSQL_WHOLE_ROW */
 	ulint	mysql_col_offset;	/*!< offset of the column in the MySQL
 					row format */
 	ulint	mysql_col_len;		/*!< length of the column in the MySQL
diff --git a/storage/innodb_plugin/include/row0upd.h b/storage/innodb_plugin/include/row0upd.h
index 635d746d5a1..4e2de9bd2ec 100644
--- a/storage/innodb_plugin/include/row0upd.h
+++ b/storage/innodb_plugin/include/row0upd.h
@@ -167,8 +167,11 @@ row_upd_changes_field_size_or_external(
 	const upd_t*	update);/*!< in: update vector */
 #endif /* !UNIV_HOTBACKUP */
 /***********************************************************//**
-Replaces the new column values stored in the update vector to the record
-given. No field size changes are allowed. */
+Replaces the new column values stored in the update vector to the
+record given. No field size changes are allowed. This function is
+usually invoked on a clustered index. The only use case for a
+secondary index is row_ins_sec_index_entry_by_modify() or its
+counterpart in ibuf_insert_to_index_page(). */
 UNIV_INTERN
 void
 row_upd_rec_in_place(
diff --git a/storage/innodb_plugin/row/row0mysql.c b/storage/innodb_plugin/row/row0mysql.c
index 78b3b2afdbf..107af481b79 100644
--- a/storage/innodb_plugin/row/row0mysql.c
+++ b/storage/innodb_plugin/row/row0mysql.c
@@ -444,7 +444,7 @@ row_mysql_convert_row_to_innobase(
 					row is used, as row may contain
 					pointers to this record! */
 {
-	mysql_row_templ_t*	templ;
+	const mysql_row_templ_t*templ;
 	dfield_t*		dfield;
 	ulint			i;
 
diff --git a/storage/innodb_plugin/row/row0sel.c b/storage/innodb_plugin/row/row0sel.c
index ea1a19eb82f..ac78a95839c 100644
--- a/storage/innodb_plugin/row/row0sel.c
+++ b/storage/innodb_plugin/row/row0sel.c
@@ -2675,21 +2675,22 @@ row_sel_store_mysql_rec(
 	row_prebuilt_t*	prebuilt,	/*!< in: prebuilt struct */
 	const rec_t*	rec,		/*!< in: Innobase record in the index
 					which was described in prebuilt's
-					template; must be protected by
-					a page latch */
+					template, or in the clustered index;
+					must be protected by a page latch */
+	ibool		rec_clust,	/*!< in: TRUE if rec is in the
+					clustered index instead of
+					prebuilt->index */
 	const ulint*	offsets)	/*!< in: array returned by
-					rec_get_offsets() */
+					rec_get_offsets(rec) */
 {
-	mysql_row_templ_t*	templ;
-	mem_heap_t*		extern_field_heap	= NULL;
-	mem_heap_t*		heap;
-	const byte*		data;
-	ulint			len;
-	ulint			i;
+	mem_heap_t*	extern_field_heap	= NULL;
+	mem_heap_t*	heap;
+	ulint		i;
 
 	ut_ad(prebuilt->mysql_template);
 	ut_ad(prebuilt->default_rec);
 	ut_ad(rec_offs_validate(rec, NULL, offsets));
+	ut_ad(!rec_get_deleted_flag(rec, rec_offs_comp(offsets)));
 
 	if (UNIV_LIKELY_NULL(prebuilt->blob_heap)) {
 		mem_heap_free(prebuilt->blob_heap);
@@ -2698,10 +2699,15 @@ row_sel_store_mysql_rec(
 
 	for (i = 0; i < prebuilt->n_template; i++) {
 
-		templ = prebuilt->mysql_template + i;
+		const mysql_row_templ_t*templ = prebuilt->mysql_template + i;
+		const byte*		data;
+		ulint			len;
+		ulint			field_no;
 
-		if (UNIV_UNLIKELY(rec_offs_nth_extern(offsets,
-						      templ->rec_field_no))) {
+		field_no = rec_clust
+			? templ->clust_rec_field_no : templ->rec_field_no;
+
+		if (UNIV_UNLIKELY(rec_offs_nth_extern(offsets, field_no))) {
 
 			/* Copy an externally stored field to the temporary
 			heap */
@@ -2729,7 +2735,7 @@ row_sel_store_mysql_rec(
 			data = btr_rec_copy_externally_stored_field(
 				rec, offsets,
 				dict_table_zip_size(prebuilt->table),
-				templ->rec_field_no, &len, heap);
+				field_no, &len, heap);
 
 			if (UNIV_UNLIKELY(!data)) {
 				/* The externally stored field
@@ -2750,8 +2756,7 @@ row_sel_store_mysql_rec(
 		} else {
 			/* Field is stored in the row. */
 
-			data = rec_get_nth_field(rec, offsets,
-						 templ->rec_field_no, &len);
+			data = rec_get_nth_field(rec, offsets, field_no, &len);
 
 			if (UNIV_UNLIKELY(templ->type == DATA_BLOB)
 			    && len != UNIV_SQL_NULL) {
@@ -3113,7 +3118,7 @@ row_sel_pop_cached_row_for_mysql(
 	row_prebuilt_t*	prebuilt)	/*!< in: prebuilt struct */
 {
 	ulint			i;
-	mysql_row_templ_t*	templ;
+	const mysql_row_templ_t*templ;
 	byte*			cached_rec;
 	ut_ad(prebuilt->n_fetch_cached > 0);
 	ut_ad(prebuilt->mysql_prefix_len <= prebuilt->mysql_row_len);
@@ -3170,15 +3175,21 @@ ibool
 row_sel_push_cache_row_for_mysql(
 /*=============================*/
 	row_prebuilt_t*	prebuilt,	/*!< in: prebuilt struct */
-	const rec_t*	rec,		/*!< in: record to push; must
-					be protected by a page latch */
-	const ulint*	offsets)	/*!< in: rec_get_offsets() */
+	const rec_t*	rec,		/*!< in: record to push, in the index
+					which was described in prebuilt's
+					template, or in the clustered index;
+					must be protected by a page latch */
+	ibool		rec_clust,	/*!< in: TRUE if rec is in the
+					clustered index instead of
+					prebuilt->index */
+	const ulint*	offsets)	/*!< in: rec_get_offsets(rec) */
 {
 	byte*	buf;
 	ulint	i;
 
 	ut_ad(prebuilt->n_fetch_cached < MYSQL_FETCH_CACHE_SIZE);
 	ut_ad(rec_offs_validate(rec, NULL, offsets));
+	ut_ad(!rec_get_deleted_flag(rec, rec_offs_comp(offsets)));
 	ut_a(!prebuilt->templ_contains_blob);
 
 	if (prebuilt->fetch_cache[0] == NULL) {
@@ -3207,7 +3218,7 @@ row_sel_push_cache_row_for_mysql(
 	if (UNIV_UNLIKELY(!row_sel_store_mysql_rec(
 				  prebuilt->fetch_cache[
 					  prebuilt->n_fetch_cached],
-				  prebuilt, rec, offsets))) {
+				  prebuilt, rec, rec_clust, offsets))) {
 		return(FALSE);
 	}
 
@@ -3608,7 +3619,8 @@ row_search_for_mysql(
 				ut_ad(!rec_get_deleted_flag(rec, comp));
 
 				if (!row_sel_store_mysql_rec(buf, prebuilt,
-							     rec, offsets)) {
+							     rec, FALSE,
+							     offsets)) {
 					/* Only fresh inserts may contain
 					incomplete externally stored
 					columns. Pretend that such
@@ -4242,7 +4254,6 @@ no_gap_lock:
 			is necessary, because we can only get the undo
 			information via the clustered index record. */
 
-			ut_ad(index != clust_index);
 			ut_ad(!dict_index_is_clust(index));
 
 			if (!lock_sec_rec_cons_read_sees(
@@ -4358,26 +4369,10 @@ requires_clust_rec:
 			goto next_rec;
 		}
 
-		if (prebuilt->need_to_access_clustered) {
-
-			result_rec = clust_rec;
-
-			ut_ad(rec_offs_validate(result_rec, clust_index,
-						offsets));
-		} else {
-			/* We used 'offsets' for the clust rec, recalculate
-			them for 'rec' */
-			offsets = rec_get_offsets(rec, index, offsets,
-						  ULINT_UNDEFINED, &heap);
-			result_rec = rec;
-		}
-
-		/* result_rec can legitimately be delete-marked
-		now that it has been established that it points to a
-		clustered index record that exists in the read view. */
+		result_rec = clust_rec;
+		ut_ad(rec_offs_validate(result_rec, clust_index, offsets));
 	} else {
 		result_rec = rec;
-		ut_ad(!rec_get_deleted_flag(rec, comp));
 	}
 
 	/* We found a qualifying record 'result_rec'. At this point,
@@ -4386,6 +4381,7 @@ requires_clust_rec:
 	ut_ad(rec_offs_validate(result_rec,
 				result_rec != rec ? clust_index : index,
 				offsets));
+	ut_ad(!rec_get_deleted_flag(result_rec, comp));
 
 	/* At this point, the clustered index record is protected
 	by a page latch that was acquired when pcur was positioned.
@@ -4410,6 +4406,7 @@ requires_clust_rec:
 		cursor. */
 
 		if (!row_sel_push_cache_row_for_mysql(prebuilt, result_rec,
+						      result_rec != rec,
 						      offsets)) {
 			/* Only fresh inserts may contain incomplete
 			externally stored columns. Pretend that such
@@ -4427,15 +4424,31 @@ requires_clust_rec:
 
 		goto next_rec;
 	} else {
-		if (prebuilt->template_type == ROW_MYSQL_DUMMY_TEMPLATE) {
+		if (UNIV_UNLIKELY
+		    (prebuilt->template_type == ROW_MYSQL_DUMMY_TEMPLATE)) {
+			/* CHECK TABLE: fetch the row */
+
+			if (result_rec != rec
+			    && !prebuilt->need_to_access_clustered) {
+				/* We used 'offsets' for the clust
+				rec, recalculate them for 'rec' */
+				offsets = rec_get_offsets(rec, index, offsets,
+							  ULINT_UNDEFINED,
+							  &heap);
+				result_rec = rec;
+			}
+
 			memcpy(buf + 4, result_rec
 			       - rec_offs_extra_size(offsets),
 			       rec_offs_size(offsets));
 			mach_write_to_4(buf,
 					rec_offs_extra_size(offsets) + 4);
 		} else {
-			if (!row_sel_store_mysql_rec(buf, prebuilt,
-						     result_rec, offsets)) {
+			/* Returning a row to MySQL */
+
+			if (!row_sel_store_mysql_rec(buf, prebuilt, result_rec,
+						     result_rec != rec,
+						     offsets)) {
 				/* Only fresh inserts may contain
 				incomplete externally stored
 				columns. Pretend that such records do
diff --git a/storage/innodb_plugin/row/row0upd.c b/storage/innodb_plugin/row/row0upd.c
index 04c3139fcc7..444003ba3f0 100644
--- a/storage/innodb_plugin/row/row0upd.c
+++ b/storage/innodb_plugin/row/row0upd.c
@@ -466,8 +466,11 @@ row_upd_changes_field_size_or_external(
 #endif /* !UNIV_HOTBACKUP */
 
 /***********************************************************//**
-Replaces the new column values stored in the update vector to the record
-given. No field size changes are allowed. */
+Replaces the new column values stored in the update vector to the
+record given. No field size changes are allowed. This function is
+usually invoked on a clustered index. The only use case for a
+secondary index is row_ins_sec_index_entry_by_modify() or its
+counterpart in ibuf_insert_to_index_page(). */
 UNIV_INTERN
 void
 row_upd_rec_in_place(