tee output.txt
show global variables;
show engine innodb status\G
show full processlist;
show global status;
select sleep(60);
show engine innodb status\G
show full processlist;
show global status;
notee;

Here are the steps to be followed while changing the log file size in mysql:

1) SET GLOBAL innodb_fast_shutdwn = 1;
2) Stop the mysqld server and check the end of the error log file to ensure that the shutdown was clean.
3) Move the existing log files to another location for extra safety.
4) Make the size change in the my.cnf and restart.

1146 Table does not exist
1054 column does not exist
1062 duplicate entry for primary key
1406 Data too long for column
1064 sql syntax error
1111 invalid use of group function
1366 incorrect integer value
1046 No database selected

And here is poor man's schema compare using good old diff command...

mysqldump nasik1 --no-data > nasik1.sql

mysqldump -h1.2.3.4 murtizapur --no-data > murtizapur.sql

diff murtizapur.sql nasik1.sql --side-by-side --suppress-common-lines | grep -v ENGINE | grep -v BTREE > to_study.txt

Or use one of the packages:

https://code.google.com/archive/p/phpmydiff/downloads

https://www.red-gate.com/products/mysql/mysql-comparison-bundle/

https://www.devart.com/dbforge/mysql/schemacompare/download.html

SET @rank = 0, @prev_val = NULL;

SELECT rank, correct FROM (
SELECT @rank := IF(@prev_val=correct,@rank,@rank+1) AS rank,
@prev_val := correct AS correct, uid
FROM quiz_user ORDER BY correct DESC
)as result WHERE uid=xxxxxxxxxxxx

It is easy to backup mysql users -

wget percona.com/get/pt-show-grants;
perl pt-show-grants

date -d"-1 day ago" +'%b%d'

equals to

mysql -Bse"select date_format(date(date_add(now() , interval 1 day)),'%b%d')"

You can write multi line comments in a stored procedure by following mysql to think that it is a version specific code.

/*!9999
Multi line comment, retained by mysql
not executed till it reaches the mysql version 9999 :))
*/

We can re-create mysql users using the percona utility.

wget percona.com/get/pt-show-grants

chmod 777 pt-show-grants

./pt-show-grants

BACKUP

innobackupex --user=USERNAME --password=PASSWORD --no-timestamp /data/backups/new_backup <--(PATH OF BACKUP)
innobackupex --apply-log /data/backups/new_backup

RESTORE

service mysql stop
mkdir /tmp/mysql
mv /var/lib/mysql/* /tmp/mysql/
innobackupex --copy-back /data/backups/new_backup <--(PATH OF BACKUP WHERE IS STORED)
chown -R mysql: /var/lib/mysql
service mysql start