[#MDEV-20864] Introduce debug option innodb_change_buffer

To diagnose a hang in slow shutdown (innodb_fast_shutdown=0), let us introduce a Boolean startup option in debug builds that will cause the contents of the InnoDB change buffer to be dumped to the server error log at startup, like this:

2019-10-19 15:13:40 139865652927488 [Note] InnoDB: Dumping the change buffer

PHYSICAL RECORD: n_fields 6; 1-byte offsets; info bits 0

 0: len 4; hex 00000004; asc     ;;

 1: len 1; hex 00; asc  ;;

 2: len 4; hex 00000010; asc     ;;

 3: len 16; hex 0000000102fe00010008860300048000; asc                 ;;

 4: len 1; hex 78; asc x;;

 5: len 4; hex 800017c3; asc     ;;

…

PHYSICAL RECORD: n_fields 6; 1-byte offsets; info bits 0

 0: len 4; hex 00000004; asc     ;;

 1: len 1; hex 00; asc  ;;

 2: len 4; hex 00000010; asc     ;;

 3: len 16; hex 0031000102fe00010008860300048000; asc  1              ;;

 4: len 1; hex 78; asc x;;

 5: len 4; hex 800017f4; asc     ;;

2019-10-19 15:13:40 139865652927488 [Note] InnoDB: Dumped the change buffer

[MDEV-20864] Introduce debug option innodb_change_buffer_dump Created: 2019-10-19 Updated: 2020-08-25 Resolved: 2019-10-19
Status:	Closed
Project:	MariaDB Server
Component/s:	Storage Engine - InnoDB
Fix Version/s:	10.2.28, 10.3.19, 10.4.9

[MDEV-20864] Introduce debug option innodb_change_buffer_dump Created: 2019-10-19 Updated: 2020-08-25 Resolved: 2019-10-19