diff --git a/mysql-test/suite/innodb/r/innodb_bug56680.result b/mysql-test/suite/innodb/r/innodb_bug56680.result
new file mode 100644
index 00000000000..c3afc3e6581
--- /dev/null
+++ b/mysql-test/suite/innodb/r/innodb_bug56680.result
@@ -0,0 +1,102 @@
+SET GLOBAL tx_isolation='REPEATABLE-READ';
+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
+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/t/innodb_bug56680.test b/mysql-test/suite/innodb/t/innodb_bug56680.test
new file mode 100644
index 00000000000..ab81ca2f8e6
--- /dev/null
+++ b/mysql-test/suite/innodb/t/innodb_bug56680.test
@@ -0,0 +1,130 @@
+#
+# Bug #56680 InnoDB may return wrong results from a case-insensitive index
+#
+-- source include/have_innodb.inc
+
+-- disable_query_log
+SET @tx_isolation_orig = @@tx_isolation;
+# 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';
+
+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;
+
+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;
+-- error 0, ER_UNKNOWN_SYSTEM_VARIABLE
+SET GLOBAL innodb_change_buffering_debug = @innodb_change_buffering_debug_orig;
diff --git a/storage/innobase/buf/buf0buf.c b/storage/innobase/buf/buf0buf.c
index 45867388a61..500088c3901 100644
--- a/storage/innobase/buf/buf0buf.c
+++ b/storage/innobase/buf/buf0buf.c
@@ -1270,6 +1270,30 @@ loop:
 		buf_awe_map_page_to_frame(block, TRUE);
 	}
 
+#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)) {
+			mutex_exit(&buf_pool->mutex);
+			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->frame;
+			goto loop;
+		}
+
+		/* Failed to evict the page; change it directly */
+	}
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
 #ifdef UNIV_SYNC_DEBUG
 	buf_block_buf_fix_inc_debug(block, file, line);
 #else
diff --git a/storage/innobase/buf/buf0flu.c b/storage/innobase/buf/buf0flu.c
index 24fa306c127..7dd6bfd9198 100644
--- a/storage/innobase/buf/buf0flu.c
+++ b/storage/innobase/buf/buf0flu.c
@@ -723,6 +723,82 @@ buf_flush_try_page(
 	return(0);
 }
 
+# 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_try_page(). */
+
+ibool
+buf_flush_page_try(
+/*===============*/
+					/* out: TRUE if flushed and
+					mutexes released */
+	buf_block_t*	block)		/*!< in/out: buffer control block */
+{
+	ut_ad(mutex_own(&buf_pool->mutex));
+	ut_ad(block->state == BUF_BLOCK_FILE_PAGE);
+	ut_ad(mutex_own(&block->mutex));
+
+	if (!buf_flush_ready_for_flush(block, 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;
+
+	block->io_fix = BUF_IO_WRITE;
+	block->flush_type = 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);
+	mutex_exit(&buf_pool->mutex);
+
+	/* 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);
+
+	mutex_enter(&buf_pool->mutex);
+	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]);
+	}
+
+	mutex_exit(&buf_pool->mutex);
+	buf_flush_buffered_writes();
+
+	return(TRUE);
+}
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
 /***************************************************************
 Flushes to disk all flushable pages within the flush area. */
 static
diff --git a/storage/innobase/buf/buf0lru.c b/storage/innobase/buf/buf0lru.c
index d3c787d1578..1dc3efd1464 100644
--- a/storage/innobase/buf/buf0lru.c
+++ b/storage/innobase/buf/buf0lru.c
@@ -320,6 +320,60 @@ buf_LRU_get_recent_limit(void)
 	return(limit);
 }
 
+/**********************************************************************
+Try to put a block from the LRU list to the free list. */
+
+ibool
+buf_LRU_free_block(
+/*===============*/
+				/* out: TRUE if freed */
+	buf_block_t*	block)	/* in/out: block to be freed */
+{
+	if (!buf_flush_ready_for_replace(block)) {
+		return(FALSE);
+	}
+
+#ifdef UNIV_DEBUG
+	if (buf_debug_prints) {
+		fprintf(stderr,
+			"Putting space %lu page %lu"
+			" to free list\n",
+			(ulong) block->space,
+			(ulong) block->offset);
+	}
+#endif /* UNIV_DEBUG */
+
+	buf_LRU_block_remove_hashed_page(block);
+
+	mutex_exit(&(buf_pool->mutex));
+	mutex_exit(&block->mutex);
+
+	/* Remove possible adaptive hash index built on the
+	page; in the case of AWE the block may not have a
+	frame at all */
+
+	if (block->frame) {
+		/* The page was declared uninitialized
+		by buf_LRU_block_remove_hashed_page().
+		We need to flag the contents of the
+		page valid (which it still is) in
+		order to avoid bogus Valgrind
+		warnings. */
+		UNIV_MEM_VALID(block->frame, UNIV_PAGE_SIZE);
+		btr_search_drop_page_hash_index(block->frame);
+		UNIV_MEM_INVALID(block->frame, UNIV_PAGE_SIZE);
+	}
+
+	ut_a(block->buf_fix_count == 0);
+
+	mutex_enter(&(buf_pool->mutex));
+	mutex_enter(&block->mutex);
+
+	buf_LRU_block_free_hashed_page(block);
+
+	return(TRUE);
+}
+
 /**********************************************************************
 Look for a replaceable block from the end of the LRU list and put it to
 the free list if found. */
@@ -348,54 +402,13 @@ buf_LRU_search_and_free_block(
 		ut_a(block->in_LRU_list);
 
 		mutex_enter(&block->mutex);
+		freed = buf_LRU_free_block(block);
+		mutex_exit(&block->mutex);
 
-		if (buf_flush_ready_for_replace(block)) {
-
-#ifdef UNIV_DEBUG
-			if (buf_debug_prints) {
-				fprintf(stderr,
-					"Putting space %lu page %lu"
-					" to free list\n",
-					(ulong) block->space,
-					(ulong) block->offset);
-			}
-#endif /* UNIV_DEBUG */
-
-			buf_LRU_block_remove_hashed_page(block);
-
-			mutex_exit(&(buf_pool->mutex));
-			mutex_exit(&block->mutex);
-
-			/* Remove possible adaptive hash index built on the
-			page; in the case of AWE the block may not have a
-			frame at all */
-
-			if (block->frame) {
-				/* The page was declared uninitialized
-				by buf_LRU_block_remove_hashed_page().
-				We need to flag the contents of the
-				page valid (which it still is) in
-				order to avoid bogus Valgrind
-				warnings. */
-				UNIV_MEM_VALID(block->frame, UNIV_PAGE_SIZE);
-				btr_search_drop_page_hash_index(block->frame);
-				UNIV_MEM_INVALID(block->frame, UNIV_PAGE_SIZE);
-			}
-
-			ut_a(block->buf_fix_count == 0);
-
-			mutex_enter(&(buf_pool->mutex));
-			mutex_enter(&block->mutex);
-
-			buf_LRU_block_free_hashed_page(block);
-			freed = TRUE;
-			mutex_exit(&block->mutex);
-
+		if (freed) {
 			break;
 		}
 
-		mutex_exit(&block->mutex);
-
 		block = UT_LIST_GET_PREV(LRU, block);
 		distance++;
 
diff --git a/storage/innobase/handler/ha_innodb.cc b/storage/innobase/handler/ha_innodb.cc
index 5a8f5479223..4c52326a58a 100644
--- a/storage/innobase/handler/ha_innodb.cc
+++ b/storage/innobase/handler/ha_innodb.cc
@@ -79,6 +79,7 @@ extern "C" {
 #include "../storage/innobase/include/dict0crea.h"
 #include "../storage/innobase/include/btr0cur.h"
 #include "../storage/innobase/include/btr0btr.h"
+#include "../storage/innobase/include/ibuf0ibuf.h"
 #include "../storage/innobase/include/fsp0fsp.h"
 #include "../storage/innobase/include/sync0sync.h"
 #include "../storage/innobase/include/fil0fil.h"
@@ -3723,17 +3724,18 @@ include_field:
 		n_requested_fields++;
 
 		templ->col_no = i;
+		templ->clust_rec_field_no = dict_col_get_clust_pos_noninline(
+			&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_noninline(
-				&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) {
@@ -3785,9 +3787,7 @@ skip_field:
 		for (i = 0; i < n_requested_fields; i++) {
 			templ = prebuilt->mysql_template + i;
 
-			templ->rec_field_no = dict_col_get_clust_pos_noninline(
-				&index->table->cols[templ->col_no],
-				clust_index);
+			templ->rec_field_no = templ->clust_rec_field_no;
 		}
 	}
 }
@@ -8990,6 +8990,13 @@ static MYSQL_SYSVAR_LONG(autoinc_lock_mode, innobase_autoinc_lock_mode,
   AUTOINC_OLD_STYLE_LOCKING,	/* Minimum value */
   AUTOINC_NO_LOCKING, 0);	/* Maximum value */
 
+#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 struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(additional_mem_pool_size),
   MYSQL_SYSVAR(autoextend_increment),
@@ -9031,6 +9038,9 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(thread_concurrency),
   MYSQL_SYSVAR(thread_sleep_delay),
   MYSQL_SYSVAR(autoinc_lock_mode),
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+  MYSQL_SYSVAR(change_buffering_debug),
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
   NULL
 };
 
diff --git a/storage/innobase/ibuf/ibuf0ibuf.c b/storage/innobase/ibuf/ibuf0ibuf.c
index d54a3378993..71ecc7ec49f 100644
--- a/storage/innobase/ibuf/ibuf0ibuf.c
+++ b/storage/innobase/ibuf/ibuf0ibuf.c
@@ -22,6 +22,7 @@ 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"
@@ -137,6 +138,11 @@ access order rules. */
 /* Buffer pool size per the maximum insert buffer size */
 #define IBUF_POOL_SIZE_PER_MAX_SIZE	2
 
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+/* Flag to control insert buffer debugging. */
+uint	ibuf_debug;
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
 /* The insert buffer control structure */
 ibuf_t*	ibuf			= NULL;
 
@@ -2819,6 +2825,72 @@ ibuf_insert(
 	}
 }
 
+/************************************************************************
+During merge, inserts to an index page a secondary index entry extracted
+from the insert buffer. */
+static
+void
+ibuf_insert_to_index_page_low(
+/*==========================*/
+	dtuple_t*	entry,	/* in: buffered entry to insert */
+	page_t*		page,	/* in: index page where the buffered entry
+				should be placed */
+	dict_index_t*	index,	/* in: record descriptor */
+	mtr_t*		mtr,	/* in: mtr */
+	page_cur_t*	page_cur)/* in: cursor positioned on the record
+				after which to insert the buffered entry */
+{
+	ulint	space;
+	ulint	page_no;
+	page_t*	bitmap_page;
+	ulint	old_bits;
+
+	if (UNIV_LIKELY
+	    (page_cur_tuple_insert(page_cur, entry, index, mtr) != NULL)) {
+		return;
+	}
+
+	/* If the record did not fit, reorganize */
+
+	btr_page_reorganize(page, index, mtr);
+
+	page_cur_search(page, index, entry, PAGE_CUR_LE, page_cur);
+
+	/* This time the record must fit */
+
+	if (UNIV_LIKELY
+	    (page_cur_tuple_insert(page_cur, entry, index, mtr) != NULL)) {
+		return;
+	}
+
+	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));
+	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 = buf_frame_get_space_id(page);
+	page_no = buf_frame_get_page_no(page);
+
+	bitmap_page = ibuf_bitmap_get_map_page(space, page_no, mtr);
+	old_bits = ibuf_bitmap_page_get_bits(bitmap_page, page_no,
+					     IBUF_BITMAP_FREE, mtr);
+
+	fprintf(stderr,
+		"InnoDB: space %lu, page %lu, bitmap bits %lu\n",
+		(ulong) space, (ulong) page_no, (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. */
@@ -2835,11 +2907,10 @@ ibuf_insert_to_index_page(
 	page_cur_t	page_cur;
 	ulint		low_match;
 	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))) {
@@ -2877,61 +2948,79 @@ dump:
 	low_match = page_cur_search(page, 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;
+
 		rec = page_cur_get_rec(&page_cur);
 
-		btr_cur_del_unmark_for_ibuf(rec, mtr);
-	} else {
-		rec = page_cur_tuple_insert(&page_cur, entry, index, mtr);
+		/* 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)));
 
-		if (rec == NULL) {
-			/* If the record did not fit, reorganize */
+		heap = mem_heap_create(1024);
 
-			btr_page_reorganize(page, index, mtr);
+		offsets = rec_get_offsets(rec, index, NULL, ULINT_UNDEFINED,
+					  &heap);
+		update = row_upd_build_sec_rec_difference_binary(
+			index, entry, rec, NULL, heap);
 
-			page_cur_search(page, index, entry,
-					PAGE_CUR_LE, &page_cur);
-
-			/* This time the record must fit */
-			if (UNIV_UNLIKELY(!page_cur_tuple_insert(
-						  &page_cur, entry, index,
-						  mtr))) {
-
-				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));
-				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);
-
-				bitmap_page = ibuf_bitmap_get_map_page(
-					buf_frame_get_space_id(page),
-					buf_frame_get_page_no(page),
-					mtr);
-				old_bits = ibuf_bitmap_page_get_bits(
-					bitmap_page,
-					buf_frame_get_page_no(page),
-					IBUF_BITMAP_FREE, mtr);
-
-				fprintf(stderr, "InnoDB: Bitmap bits %lu\n",
-					(ulong) old_bits);
-
-				fputs("InnoDB: Submit a detailed bug report"
-				      " to http://bugs.mysql.com\n", stderr);
-			}
+		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, mtr);
+updated_in_place:
+			mem_heap_free(heap);
+			return;
 		}
+
+		/* 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;
+
+		/* 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)) {
+			/* This is the easy case. Do something similar
+			to btr_cur_update_in_place(). */
+			row_upd_rec_in_place(rec, offsets, update);
+			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(page, 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, page, index, mtr,
+					      &page_cur);
+		lock_rec_restore_from_page_infimum(rec, page);
+	} else {
+		ibuf_insert_to_index_page_low(entry, page, index, mtr,
+					      &page_cur);
 	}
 }
 
diff --git a/storage/innobase/include/buf0flu.h b/storage/innobase/include/buf0flu.h
index 322848509f4..e52c22b8f57 100644
--- a/storage/innobase/include/buf0flu.h
+++ b/storage/innobase/include/buf0flu.h
@@ -38,6 +38,20 @@ buf_flush_init_for_writing(
 	dulint	newest_lsn,	/* in: newest modification lsn to the page */
 	ulint	space,		/* in: space id */
 	ulint	page_no);	/* in: page number */
+# 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_try_page(). */
+
+ibool
+buf_flush_page_try(
+/*===============*/
+					/* out: TRUE if flushed and
+					mutexes released */
+	buf_block_t*	block);		/*!< in/out: buffer control block */
+#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/innobase/include/buf0lru.h b/storage/innobase/include/buf0lru.h
index 6d26fd4d3b2..777e55a350d 100644
--- a/storage/innobase/include/buf0lru.h
+++ b/storage/innobase/include/buf0lru.h
@@ -66,6 +66,14 @@ buf_LRU_get_recent_limit(void);
 /*==========================*/
 			/* out: the limit; zero if could not determine it */
 /**********************************************************************
+Try to put a block from the LRU list to the free list. */
+
+ibool
+buf_LRU_free_block(
+/*===============*/
+				/* out: TRUE if freed */
+	buf_block_t*	block);	/* in/out: block to be freed */
+/**********************************************************************
 Look for a replaceable block from the end of the LRU list and put it to
 the free list if found. */
 
diff --git a/storage/innobase/include/ibuf0ibuf.h b/storage/innobase/include/ibuf0ibuf.h
index 77fefe2020b..d6d7a918b62 100644
--- a/storage/innobase/include/ibuf0ibuf.h
+++ b/storage/innobase/include/ibuf0ibuf.h
@@ -18,6 +18,11 @@ Created 7/19/1997 Heikki Tuuri
 #include "ibuf0types.h"
 #include "fsp0fsp.h"
 
+#if defined UNIV_DEBUG || defined UNIV_IBUF_DEBUG
+/* Flag to control insert buffer debugging. */
+extern uint		ibuf_debug;
+#endif /* UNIV_DEBUG || UNIV_IBUF_DEBUG */
+
 extern ibuf_t*	ibuf;
 
 /**********************************************************************
diff --git a/storage/innobase/include/rem0rec.h b/storage/innobase/include/rem0rec.h
index abc204bb583..58762fc3111 100644
--- a/storage/innobase/include/rem0rec.h
+++ b/storage/innobase/include/rem0rec.h
@@ -19,6 +19,9 @@ if and only if the record is the first user record on a non-leaf
 B-tree page that is the leftmost page on its level
 (PAGE_LEVEL is nonzero and FIL_PAGE_PREV is FIL_NULL). */
 #define REC_INFO_MIN_REC_FLAG	0x10UL
+/* The deleted flag in info bits */
+#define REC_INFO_DELETED_FLAG	0x20UL	/* when bit is set to 1, it means the
+					record has been delete marked */
 
 /* Number of extra bytes in an old-style record,
 in addition to the data and the offsets */
diff --git a/storage/innobase/include/rem0rec.ic b/storage/innobase/include/rem0rec.ic
index d91fb4c4391..df66bb13aeb 100644
--- a/storage/innobase/include/rem0rec.ic
+++ b/storage/innobase/include/rem0rec.ic
@@ -98,9 +98,6 @@ and the shift needed to obtain each bit-field of the record. */
 #define	REC_INFO_BITS_MASK	0xF0UL
 #define REC_INFO_BITS_SHIFT	0
 
-/* The deleted flag in info bits */
-#define REC_INFO_DELETED_FLAG	0x20UL	/* when bit is set to 1, it means the
-					record has been delete marked */
 /* The following masks are used to filter the SQL null bit from
 one-byte and two-byte offsets */
 
diff --git a/storage/innobase/include/row0mysql.h b/storage/innobase/include/row0mysql.h
index 488177791a4..52b13838cc7 100644
--- a/storage/innobase/include/row0mysql.h
+++ b/storage/innobase/include/row0mysql.h
@@ -485,6 +485,10 @@ 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/innobase/include/row0upd.h b/storage/innobase/include/row0upd.h
index efbc6d6facf..034b1dafb17 100644
--- a/storage/innobase/include/row0upd.h
+++ b/storage/innobase/include/row0upd.h
@@ -129,9 +129,11 @@ row_upd_changes_field_size_or_external(
 	const ulint*	offsets,/* in: rec_get_offsets(rec, index) */
 	upd_t*		update);/* in: update vector */
 /***************************************************************
-Replaces the new column values stored in the update vector to the record
-given. No field size changes are allowed. This function is used only for
-a clustered index */
+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(). */
 
 void
 row_upd_rec_in_place(
diff --git a/storage/innobase/row/row0mysql.c b/storage/innobase/row/row0mysql.c
index a0f54f7288e..99738115cc7 100644
--- a/storage/innobase/row/row0mysql.c
+++ b/storage/innobase/row/row0mysql.c
@@ -400,7 +400,7 @@ 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/innobase/row/row0sel.c b/storage/innobase/row/row0sel.c
index ad15d0798a2..e03d3d79768 100644
--- a/storage/innobase/row/row0sel.c
+++ b/storage/innobase/row/row0sel.c
@@ -2601,20 +2601,21 @@ row_sel_store_mysql_rec(
 	row_prebuilt_t*	prebuilt,	/* in: prebuilt struct */
 	rec_t*		rec,		/* in: Innobase record in the index
 					which was described in prebuilt's
-					template */
+					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;
-	byte*			data;
-	ulint			len;
 	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);
@@ -2623,10 +2624,15 @@ 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;
+		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 */
@@ -2652,15 +2658,13 @@ row_sel_store_mysql_rec(
 			causes an assert */
 
 			data = btr_rec_copy_externally_stored_field(
-				rec, offsets, templ->rec_field_no,
-				&len, heap);
+				rec, offsets, field_no, &len, heap);
 
 			ut_a(len != UNIV_SQL_NULL);
 		} 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) {
@@ -3019,7 +3023,7 @@ 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);
@@ -3075,14 +3079,19 @@ void
 row_sel_push_cache_row_for_mysql(
 /*=============================*/
 	row_prebuilt_t*	prebuilt,	/* in: prebuilt struct */
-	rec_t*		rec,		/* in: record to push */
-	const ulint*	offsets)	/* in: rec_get_offsets() */
+	rec_t*		rec,		/* in: Innobase record in the index
+					which was described in prebuilt's
+					template, or in the clustered index */
+	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) {
@@ -3111,7 +3120,7 @@ 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))) {
 		ut_error;
 	}
 
@@ -3500,7 +3509,8 @@ row_search_for_mysql(
 							 rec, offsets));
 #endif
 				if (!row_sel_store_mysql_rec(buf, prebuilt,
-							     rec, offsets)) {
+							     rec, FALSE,
+							     offsets)) {
 					err = DB_TOO_BIG_RECORD;
 
 					/* We let the main loop to do the
@@ -4233,19 +4243,8 @@ 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 = clust_rec;
+		ut_ad(rec_offs_validate(result_rec, clust_index, offsets));
 	} else {
 		result_rec = rec;
 	}
@@ -4256,6 +4255,7 @@ 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));
 
 	if ((match_mode == ROW_SEL_EXACT
 	     || prebuilt->n_rows_fetched >= MYSQL_FETCH_CACHE_THRESHOLD)
@@ -4276,7 +4276,7 @@ requires_clust_rec:
 		cursor. */
 
 		row_sel_push_cache_row_for_mysql(prebuilt, result_rec,
-						 offsets);
+						 result_rec != rec, offsets);
 		if (prebuilt->n_fetch_cached == MYSQL_FETCH_CACHE_SIZE) {
 
 			goto got_row;
@@ -4284,15 +4284,31 @@ 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)) {
 				err = DB_TOO_BIG_RECORD;
 
 				goto lock_wait_or_error;
diff --git a/storage/innobase/row/row0upd.c b/storage/innobase/row/row0upd.c
index 034b7010410..0790cfe02e2 100644
--- a/storage/innobase/row/row0upd.c
+++ b/storage/innobase/row/row0upd.c
@@ -430,9 +430,11 @@ row_upd_changes_field_size_or_external(
 }
 
 /***************************************************************
-Replaces the new column values stored in the update vector to the record
-given. No field size changes are allowed. This function is used only for
-a clustered index */
+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(). */
 
 void
 row_upd_rec_in_place(