Bug#4692 - DISABLE/ENABLE KEYS waste a space

Disabling and enabling indexes on a non-empty table grows the
index file.

Disabling indexes just sets a flag per non-unique index and does not
free the index blocks of the affected indexes. Re-enabling indexes
creates new indexes with new blocks. The old blocks remain unused
in the index file.

Fixed by dropping and re-creating all indexes if non-empty disabled
indexes exist when enabling indexes. Dropping all indexes resets
the internal end-of-file marker to the end of the index file header.
It also clears the root block pointers of every index and clears the
deleted blocks chains. This way all blocks are declared as free.


myisam/mi_check.c:
  Bug#4692 - DISABLE/ENABLE KEYS waste a space
  Added function mi_drop_all_indexes() to support drop of all indexes
  in case we want to re-enable non-empty disabled indexes.
  Changed mi_repair(), mi_repair_by_sort(), and mi_repair_parallel()
  to use the new function instead of duplicate drop index code.
mysql-test/r/myisam.result:
  Bug#4692 - DISABLE/ENABLE KEYS waste a space
  Added test result.
mysql-test/t/myisam.test:
  Bug#4692 - DISABLE/ENABLE KEYS waste a space
  Added test.

mysql-test/r/myisam.result

@@ -1806,4 +1806,29 @@ SELECT a FROM t1 FORCE INDEX (inx) WHERE a=1;
 a
 1
 DROP TABLE t1;
+CREATE TABLE t1 (c1 INT, c2 INT, UNIQUE INDEX (c1), INDEX (c2)) ENGINE=MYISAM;
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	10	Fixed	0	#	#	#	1024	#	#	#	#	#	#	#		
+INSERT INTO t1 VALUES (1,1);
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	10	Fixed	1	#	#	#	3072	#	#	#	#	#	#	#		
+ALTER TABLE t1 DISABLE KEYS;
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	10	Fixed	1	#	#	#	3072	#	#	#	#	#	#	#		
+ALTER TABLE t1 ENABLE KEYS;
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	10	Fixed	1	#	#	#	3072	#	#	#	#	#	#	#		
+ALTER TABLE t1 DISABLE KEYS;
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	10	Fixed	1	#	#	#	3072	#	#	#	#	#	#	#		
+ALTER TABLE t1 ENABLE KEYS;
+SHOW TABLE STATUS LIKE 't1';
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
+t1	MyISAM	10	Fixed	1	#	#	#	3072	#	#	#	#	#	#	#		
+DROP TABLE t1;
 End of 5.0 tests

mysql-test/t/myisam.test

@@ -1161,4 +1161,30 @@ ALTER TABLE t1 ENABLE KEYS;
 SELECT a FROM t1 FORCE INDEX (inx) WHERE a=1;
 DROP TABLE t1;
 
+#
+# Bug#4692 - DISABLE/ENABLE KEYS waste a space
+#
+CREATE TABLE t1 (c1 INT, c2 INT, UNIQUE INDEX (c1), INDEX (c2)) ENGINE=MYISAM;
+--replace_column 6 # 7 # 8 # 10 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+INSERT INTO t1 VALUES (1,1);
+--replace_column 6 # 7 # 8 # 10 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+ALTER TABLE t1 DISABLE KEYS;
+--replace_column 6 # 7 # 8 # 10 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+ALTER TABLE t1 ENABLE KEYS;
+--replace_column 6 # 7 # 8 # 10 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+ALTER TABLE t1 DISABLE KEYS;
+--replace_column 6 # 7 # 8 # 10 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+ALTER TABLE t1 ENABLE KEYS;
+--replace_column 6 # 7 # 8 # 10 # 11 # 12 # 13 # 14 # 15 # 16 #
+SHOW TABLE STATUS LIKE 't1';
+#--exec ls -log var/master-data/test/t1.MYI
+#--exec myisamchk -dvv var/master-data/test/t1.MYI
+#--exec myisamchk -iev var/master-data/test/t1.MYI
+DROP TABLE t1;
+
 --echo End of 5.0 tests