Shantanu's Blog

There is a very easy way to compare files using python.

import filecmp
dc = filecmp.dircmp('dirA', 'dirB')

Now you can find common files as well as files missing in second directory using common, left_only methods.

dc.common
dc.left_only
dc.right_only

Or simply ask for the full report.

dc.report_full_closure()

Easy and neat!

While troubleshooting mysql issue, the first place to check is error log. If the error log is clean, then the next option to evaluate is slow query log

# enable slow query log
mysql> set global slow_query_log = on;

# change the default 10 seconds to 1 second
# make sure that the queries not using indexes are logged
SET GLOBAL long_query_time=1;
SET GLOBAL log_queries_not_using_indexes=1;

# If the slow log is growing too fast, feel free to again set the variables back to how they were:

SET GLOBAL long_query_time=10;
SET GLOBAL log_queries_not_using_indexes=0;

# or disable the slow query log
set global slow_query_log = off;

The unicode characters are not allowed to be stored in latin1
You will get an error as shown below:

drop table todel;
create table todel (name varchar(100)) DEFAULT CHARSET=latin1;

insert into todel values ('हिदी' )
Error in query (1366): Incorrect string value: '\xE0\xA4\xB9\xE0\xA4\xBF...' for column 'name' at row 1

insert into todel values (convert ('हिदी' using binary));
select convert(convert(name using binary) using utf8) from todel;

The work-around is to store the record as binary and while selecting, use convert function twice as shown above.
_____

There is a better way though. Why not to use utf8 encoding for the entire table?

drop table todel;
create table todel (name varchar(100)) DEFAULT CHARSET=utf8;

insert into todel values ('हिदी' );
select * from todel;
_____

You think that altering the table to utf8 will solve this issue?

alter table todel default charset=utf8;

No. Because even if the default table type is now utf8, the columns are still latin1

 mysql> show create table todel;
+-------+---------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                        |
+-------+---------------------------------------------------------------------------------------------------------------------+
| todel | CREATE TABLE `todel` (
  `name` varchar(100) CHARACTER SET latin1 DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

alter table todel modify name varchar(100) character set utf8 ;

Now even if we have column as well as table type utf8, we still get junk characters instead of unicode.

mysql> select * from todel;
+---------------------------+
| name                      |
+---------------------------+
| हिदी              |
+---------------------------+
1 row in set (0.00 sec)

The bad news is that the convert query that was working fine earlier has now stopped working as expected.

mysql> select convert(convert(name using binary) using utf8) from todel;
+------------------------------------------------+
| convert(convert(name using binary) using utf8) |
+------------------------------------------------+
| हिदी                                   |
+------------------------------------------------+
1 row in set (0.00 sec)

The unicode data is lost in the conversion.
_____

So the correct solution would be to add a utf8 column to latin1 table and update that column data with correct unicode string.
Let's start all over again:

drop table todel;
create table todel (name varchar(100)) DEFAULT CHARSET=latin1;
insert into todel values (convert ('हिदी' using binary));
select convert(convert(name using binary) using utf8) from todel;

alter table todel add column hindi varchar(100) character set utf8;

update todel set hindi = convert(convert(name using binary) using utf8) ;

mysql> select convert(convert(name using binary) using utf8), hindi from todel;
+------------------------------------------------+--------------+
| convert(convert(name using binary) using utf8) | hindi        |
+------------------------------------------------+--------------+
| हिदी                                           | हिदी         |
+------------------------------------------------+--------------+
1 row in set (0.00 sec)

_____

Now the problem is that the application is not aware of this new column called "hindi" and it is still using column "name". We need an insert and update trigger to keep correcting the values in the hindi column. Something like this...

delimiter |
CREATE TRIGGER todel_bi after INSERT ON todel
  FOR EACH ROW
  BEGIN
    UPDATE todel SET hindi = convert(convert(name using binary) using utf8) WHERE id = NEW.id;
  END;
|

insert into todel (id, name) values (2, (convert ('मराठी' using binary)));

I thought the after insert trigger would solve this issue, but I get an error.

ERROR 1442 (HY000): Can't update table in trigger because it is already used by statement which invoked this stored function/trigger.

Now I need to write a stored procedure that inserts the record in the target table and change the code accordingly (that will call the procedure).
_____

So we are back where we started. Why not simply replace the name column with this new unicode aware column?

drop table todel;
create table todel (name varchar(100)) DEFAULT CHARSET=latin1;
insert into todel values (convert ('हिदी' using binary));

alter table todel add column hindi varchar(100) character set utf8;
update todel set hindi = convert(convert(name using binary) using utf8) ;
alter table todel drop column name;
alter table todel change column hindi name varchar(100) character set utf8;