MDEV-21511 Wrong estimate of affected BLOB columns in update

During update, rollback, or MVCC read, we may miscalculate
the number of off-page columns, and thus the size of the
clustered index record. The function btr_push_update_extern_fields()
is mostly redundant, because the off-page columns would also be
moved by row_upd_index_replace_new_col_val(), which is invoked
via row_upd_index_replace_new_col_vals().

btr_push_update_extern_fields(): Remove.

This is based on
mysql/mysql-server@1fa475b85d24de4b9ce2958c0eed738c221fc82c
which refines a fix for a recovery bug fix
mysql/mysql-server@ce0a1e85e24e48b8171f767b44330da635a6ea0a
in MySQL 5.7.5.

No test case was provided by Oracle.
Some of the changed code is being covered by the existing test
innodb.blob-crash.

storage/innobase/btr/btr0cur.cc

 /*****************************************************************************
 
-Copyright (c) 1994, 2018, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 1994, 2019, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2008, Google Inc.
 Copyright (c) 2012, Facebook Inc.
-Copyright (c) 2015, 2019, MariaDB Corporation.
+Copyright (c) 2015, 2020, MariaDB Corporation.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -4374,7 +4374,9 @@ btr_cur_pessimistic_update(
 
 	ut_ad(!page_is_comp(page) || !rec_get_node_ptr_flag(rec));
 	ut_ad(rec_offs_validate(rec, index, *offsets));
-	n_ext += btr_push_update_extern_fields(new_entry, update, entry_heap);
+
+	/* Get number of externally stored columns in updated record */
+	n_ext = dtuple_get_n_ext(new_entry);
 
 	if ((flags & BTR_NO_UNDO_LOG_FLAG)
 	    && rec_offs_any_extern(*offsets)) {
@@ -6593,84 +6595,6 @@ btr_cur_unmark_extern_fields(
 	}
 }
 
-/*******************************************************************//**
-Flags the data tuple fields that are marked as extern storage in the
-update vector.  We use this function to remember which fields we must
-mark as extern storage in a record inserted for an update.
-@return number of flagged external columns */
-ulint
-btr_push_update_extern_fields(
-/*==========================*/
-	dtuple_t*	tuple,	/*!< in/out: data tuple */
-	const upd_t*	update,	/*!< in: update vector */
-	mem_heap_t*	heap)	/*!< in: memory heap */
-{
-	ulint			n_pushed	= 0;
-	ulint			n;
-	const upd_field_t*	uf;
-
-	uf = update->fields;
-	n = upd_get_n_fields(update);
-
-	for (; n--; uf++) {
-		if (dfield_is_ext(&uf->new_val)) {
-			dfield_t*	field
-				= dtuple_get_nth_field(tuple, uf->field_no);
-
-			if (!dfield_is_ext(field)) {
-				dfield_set_ext(field);
-				n_pushed++;
-			}
-
-			switch (uf->orig_len) {
-				byte*	data;
-				ulint	len;
-				byte*	buf;
-			case 0:
-				break;
-			case BTR_EXTERN_FIELD_REF_SIZE:
-				/* Restore the original locally stored
-				part of the column.  In the undo log,
-				InnoDB writes a longer prefix of externally
-				stored columns, so that column prefixes
-				in secondary indexes can be reconstructed. */
-				dfield_set_data(field,
-						(byte*) dfield_get_data(field)
-						+ dfield_get_len(field)
-						- BTR_EXTERN_FIELD_REF_SIZE,
-						BTR_EXTERN_FIELD_REF_SIZE);
-				dfield_set_ext(field);
-				break;
-			default:
-				/* Reconstruct the original locally
-				stored part of the column.  The data
-				will have to be copied. */
-				ut_a(uf->orig_len > BTR_EXTERN_FIELD_REF_SIZE);
-
-				data = (byte*) dfield_get_data(field);
-				len = dfield_get_len(field);
-
-				buf = (byte*) mem_heap_alloc(heap,
-							     uf->orig_len);
-				/* Copy the locally stored prefix. */
-				memcpy(buf, data,
-				       uf->orig_len
-				       - BTR_EXTERN_FIELD_REF_SIZE);
-				/* Copy the BLOB pointer. */
-				memcpy(buf + uf->orig_len
-				       - BTR_EXTERN_FIELD_REF_SIZE,
-				       data + len - BTR_EXTERN_FIELD_REF_SIZE,
-				       BTR_EXTERN_FIELD_REF_SIZE);
-
-				dfield_set_data(field, buf, uf->orig_len);
-				dfield_set_ext(field);
-			}
-		}
-	}
-
-	return(n_pushed);
-}
-
 /*******************************************************************//**
 Returns the length of a BLOB part stored on the header page.
 @return part length */

storage/innobase/include/btr0cur.h

 /*****************************************************************************
 
-Copyright (c) 1994, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2019, MariaDB Corporation.
+Copyright (c) 1994, 2019, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2017, 2020, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -755,18 +755,6 @@ btr_rec_copy_externally_stored_field(
 	ulint*			len,
 	mem_heap_t*		heap);
 
-/*******************************************************************//**
-Flags the data tuple fields that are marked as extern storage in the
-update vector.  We use this function to remember which fields we must
-mark as extern storage in a record inserted for an update.
-@return number of flagged external columns */
-ulint
-btr_push_update_extern_fields(
-/*==========================*/
-	dtuple_t*	tuple,	/*!< in/out: data tuple */
-	const upd_t*	update,	/*!< in: update vector */
-	mem_heap_t*	heap)	/*!< in: memory heap */
-	MY_ATTRIBUTE((nonnull));
 /***********************************************************//**
 Sets a secondary index record's delete mark to the given value. This
 function is only used by the insert buffer merge mechanism. */

storage/innobase/include/rem0rec.ic

 /*****************************************************************************
 
-Copyright (c) 1994, 2015, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2019, MariaDB Corporation.
+Copyright (c) 1994, 2019, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2017, 2020, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -1626,6 +1626,7 @@ rec_get_converted_size(
 
 	data_size = dtuple_get_data_size(dtuple, 0);
 
+	ut_ad(n_ext == dtuple_get_n_ext(dtuple));
 	extra_size = rec_get_converted_extra_size(
 		data_size, dtuple_get_n_fields(dtuple), n_ext);
 

storage/innobase/trx/trx0rec.cc

 /*****************************************************************************
 
-Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2019, MariaDB Corporation.
+Copyright (c) 1996, 2019, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2017, 2020, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -2448,12 +2448,14 @@ trx_undo_prev_version_build(
 
 		entry = row_rec_to_index_entry(
 			rec, index, offsets, &n_ext, heap);
-		n_ext += btr_push_update_extern_fields(entry, update, heap);
 		/* The page containing the clustered index record
 		corresponding to entry is latched in mtr.  Thus the
 		following call is safe. */
 		row_upd_index_replace_new_col_vals(entry, index, update, heap);
 
+		/* Get number of externally stored columns in updated record */
+		n_ext = dtuple_get_n_ext(entry);
+
 		buf = static_cast<byte*>(mem_heap_alloc(
 			heap, rec_get_converted_size(index, entry, n_ext)));