Failure upon upgrade from 5.7.23 to 10.2 and 10.3, pagesize 4K

https://travis-ci.org/elenst/travis-tests/jobs/409014461

# 2018-07-28T04:59:50 [24239] Running mysql_upgrade:

# 2018-07-28T04:59:50 [24239]   "/home/travis/server/bin/mysql_upgrade" --host=127.0.0.1 --port=19300 -uroot

ERROR 1071 (42000) at line 596: Specified key was too long; max key length is 768 bytes

ERROR 1071 (42000) at line 600: Specified key was too long; max key length is 768 bytes

ERROR 1071 (42000) at line 603: Specified key was too long; max key length is 768 bytes

FATAL ERROR: Upgrade failed

# 2018-07-28T04:59:51 [24239][ERROR] mysql_upgrade failed

Nothing special is needed on MySQL side, apart from bootstrap with page_size 4K. The pre-created datadir is attached. The exact steps to create it were these:

• start MySQL 5.7.23 in initialize mode:

  /data/bld/mysql-5.7/bin/mysqld --no-defaults --basedir=/data/bld/mysql-5.7 --datadir=/data/bld/mysql-5.7/data --log-error=/data/bld/mysql-5.7/data/log.err --loose-lc-messages-dir= --loose-language= --port=3306 --socket=/tmp/mysql.sock --tmpdir=/tmp --loose-core-file --initialize --innodb-page-size=4K

• start the same server in normal mode, with skip-grant-tables:

  /data/bld/mysql-5.7/bin/mysqld --no-defaults --basedir=/data/bld/mysql-5.7 --datadir=/data/bld/mysql-5.7/data --log-error=/data/bld/mysql-5.7/data/log.err --loose-lc-messages-dir= --loose-language= --port=3306 --socket=/tmp/mysql.sock --tmpdir=/tmp --loose-core-file --innodb-page-size=4K --skip-grant-tables

• execute

  MySQL [(none)]> flush privileges;

  Query OK, 0 rows affected (0.01 sec)

  MySQL [(none)]> set password for root@localhost = '';

  Query OK, 0 rows affected (0.00 sec)

• shut down the server normally.

Note: Upon initialization, MySQL sets one-time password which it writes to the error log. MySQL one-time passwords don't work for me reliably on some reason, that's why I reset it using skip-grant-tables. It's not important for the upgrade issue.

To reproduce the upgrade problem, start recent MariaDB 10.2 on the created datadir (which you either created as above, or unpacked from the attachment). Don't forget innodb_page_size=4K.

The server should complain in the error log but start all right. Then run mysql_upgrade with root user without parameters, like

bin/mysql_upgrade -uroot --protocol=tcp

It complains a lot while running, but the real (fatal) problem happens on phase 4/7:

Phase 4/7: Running 'mysql_fix_privilege_tables'

ERROR 1071 (42000) at line 596: Specified key was too long; max key length is 768 bytes

ERROR 1071 (42000) at line 600: Specified key was too long; max key length is 768 bytes

ERROR 1071 (42000) at line 603: Specified key was too long; max key length is 768 bytes

FATAL ERROR: Upgrade failed