MDEV-19974 InnoDB: Cannot load compressed BLOB

Problem:
=======
	During online alter, fts tokenization thread uses new table page size
to read the externally stored page from old table. If the alter changes
the page size then it leads to failure of alter table.

Solution:
=========
	fts tokenization thread should use old table page size to read the
externally stored page from old table.

mysql-test/suite/innodb_fts/r/innodb_fts_misc.result

@@ -1384,3 +1384,8 @@ SELECT * FROM t1 WHERE MATCH (a) AGAINST ('+"good database"' IN BOOLEAN MODE);
 id	a
 1	know mysql good database
 DROP TABLE t1;
+CREATE TABLE t1(f1 TEXT, FULLTEXT KEY(f1))ENGINE=InnoDB;
+INSERT INTO t1 VALUES(repeat("this is the test case", 500));
+ALTER TABLE t1 KEY_BLOCK_SIZE=4;
+ALTER TABLE t1 KEY_BLOCK_SIZE=0;
+DROP TABLE t1;

mysql-test/suite/innodb_fts/t/innodb_fts_misc.test

@@ -1331,3 +1331,11 @@ INSERT INTO t1 (a) VALUES
 SELECT * FROM t1 WHERE MATCH (a) AGAINST ('+"good database"' IN BOOLEAN MODE);
 
 DROP TABLE t1;
+
+# MDEV-19974 InnoDB: Cannot load compressed BLOB
+CREATE TABLE t1(f1 TEXT, FULLTEXT KEY(f1))ENGINE=InnoDB;
+INSERT INTO t1 VALUES(repeat("this is the test case", 500));
+ALTER TABLE t1 KEY_BLOCK_SIZE=4;
+ALTER TABLE t1 KEY_BLOCK_SIZE=0;
+DROP TABLE t1;
+

storage/innobase/include/row0ftsort.h

@@ -59,6 +59,8 @@ struct fts_psort_t;
 struct fts_psort_common_t {
 	row_merge_dup_t*	dup;		/*!< descriptor of FTS index */
 	dict_table_t*		new_table;	/*!< source table */
+	/* Old table page size */
+	page_size_t		old_page_size;
 	trx_t*			trx;		/*!< transaction */
 	fts_psort_t*		all_info;	/*!< all parallel sort info */
 	os_event_t		sort_event;	/*!< sort event */
@@ -190,26 +192,27 @@ row_merge_create_fts_sort_index(
 				instead of 8 bytes integer to
 				store Doc ID during sort */
 
-/********************************************************************//**
-Initialize FTS parallel sort structures.
+/** Initialize FTS parallel sort structures.
+@param[in]	trx		transaction
+@param[in,out]	dup		descriptor of FTS index being created
+@param[in]	new_table	table where indexes are created
+@param[in]	opt_doc_id_size	whether to use 4 bytes instead of 8 bytes
+				integer to store Doc ID during sort
+@param[in]	old_page_size	page size of the old table during alter
+@param[out]	psort		parallel sort info to be instantiated
+@param[out]	merge		parallel merge info to be instantiated
 @return TRUE if all successful */
 ibool
 row_fts_psort_info_init(
-/*====================*/
-	trx_t*			trx,	/*!< in: transaction */
-	row_merge_dup_t*	dup,	/*!< in,own: descriptor of
-					FTS index being created */
-	const dict_table_t*	new_table,/*!< in: table where indexes are
-					created */
+	trx_t*			trx,
+	row_merge_dup_t*	dup,
+	const dict_table_t*	new_table,
 	ibool			opt_doc_id_size,
-					/*!< in: whether to use 4 bytes
-					instead of 8 bytes integer to
-					store Doc ID during sort */
-	fts_psort_t**		psort,	/*!< out: parallel sort info to be
-					instantiated */
-	fts_psort_t**		merge)	/*!< out: parallel merge info
-					to be instantiated */
+	const page_size_t	old_page_size,
+	fts_psort_t**		psort,
+	fts_psort_t**		merge)
 	MY_ATTRIBUTE((nonnull));
+
 /********************************************************************//**
 Clean up and deallocate FTS parallel sort structures, and close
 temparary merge sort files */

storage/innobase/row/row0ftsort.cc

@@ -159,25 +159,26 @@ row_merge_create_fts_sort_index(
 
 	return(new_index);
 }
-/*********************************************************************//**
-Initialize FTS parallel sort structures.
+
+/** Initialize FTS parallel sort structures.
+@param[in]	trx		transaction
+@param[in,out]	dup		descriptor of FTS index being created
+@param[in]	new_table	table where indexes are created
+@param[in]	opt_doc_id_size	whether to use 4 bytes instead of 8 bytes
+				integer to store Doc ID during sort
+@param[in]	old_page_size	page size of the old table during alter
+@param[out]	psort		parallel sort info to be instantiated
+@param[out]	merge		parallel merge info to be instantiated
 @return TRUE if all successful */
 ibool
 row_fts_psort_info_init(
-/*====================*/
-	trx_t*			trx,	/*!< in: transaction */
-	row_merge_dup_t*	dup,	/*!< in,own: descriptor of
-					FTS index being created */
-	const dict_table_t*	new_table,/*!< in: table on which indexes are
-					created */
-	ibool			opt_doc_id_size,
-					/*!< in: whether to use 4 bytes
-					instead of 8 bytes integer to
-					store Doc ID during sort */
-	fts_psort_t**		psort,	/*!< out: parallel sort info to be
-					instantiated */
-	fts_psort_t**		merge)	/*!< out: parallel merge info
-					to be instantiated */
+        trx_t*                  trx,
+        row_merge_dup_t*        dup,
+        const dict_table_t*     new_table,
+        ibool                   opt_doc_id_size,
+        const page_size_t       old_page_size,
+        fts_psort_t**           psort,
+        fts_psort_t**           merge)
 {
 	ulint			i;
 	ulint			j;
@@ -210,6 +211,7 @@ row_fts_psort_info_init(
 
 	common_info->dup = dup;
 	common_info->new_table = (dict_table_t*) new_table;
+	common_info->old_page_size = old_page_size;
 	common_info->trx = trx;
 	common_info->all_info = psort_info;
 	common_info->sort_event = os_event_create(0);
@@ -803,7 +805,8 @@ DECLARE_THREAD(fts_parallel_tokenization)(
 	block = psort_info->merge_block;
 	crypt_block = psort_info->crypt_block;
 
-	const page_size_t&	page_size = dict_table_page_size(table);
+	const page_size_t	old_page_size =
+			psort_info->psort_common->old_page_size;
 
 	row_merge_fts_get_next_doc_item(psort_info, &doc_item);
 
@@ -833,7 +836,7 @@ loop:
 				doc.text.f_str =
 					btr_copy_externally_stored_field(
 						&doc.text.f_len, data,
-						page_size, data_len, blob_heap);
+						old_page_size, data_len, blob_heap);
 			} else {
 				doc.text.f_str = data;
 				doc.text.f_len = data_len;

storage/innobase/row/row0merge.cc

@@ -4678,6 +4678,7 @@ row_merge_build_indexes(
 			created */
 			if (!row_fts_psort_info_init(
 					trx, dup, new_table, opt_doc_id_size,
+					dict_table_page_size(old_table),
 					&psort_info, &merge_info)) {
 				error = DB_CORRUPTION;
 				goto func_exit;