```sh
mysql> select count(*) from users;
+----------+
| count(*) |
+----------+
| 25305798 |
+----------+
1 row in set (10.24 sec)

# Inplace, rebuilds table, allows DML
mysql -u root experiments --execute="alter table users add column ptfun varchar(50) default 'pt fun'"
106s (1min 46s)

# Starts with 1k chunk for first select query followed by 30k and then straight away to 51-56k
pt-online-schema-change --alter "add column ptfun varchar(50) default 'pt fun'" D=experiments,t=users,u=root --execute --alter-foreign-keys-method rebuild_constraints
297s (4min 57s)

# made changes to the online schema code to work on host, instead of socket
# With 9k chunks:
osc_cli copy --ddl-file=alter.sql --database=experiments --socket=/tmp/mysql.socket --mysql-user=root --mysql-password= --outfile-dir=/Users/rishabhpugalia/www/dev/percona/outfile
689s (10min 29s)

# With 60k chunks:
osc_cli copy --ddl-file=alter.sql --database=experiments --socket=/tmp/mysql.socket --mysql-user=root --mysql-password= --outfile-dir=/Users/rishabhpugalia/www/dev/percona/outfile --chunk-size=15000000
559s (9m 19s)

2m vs 5m vs 10.5m || 9.2m
```

For FB, had to make these changes:

```sh
$ cat /etc/my.cnf
[mysqld]

binlog-format = 'STATEMENT'
secure-file-priv = ''
```

In `db.py`, made this change in `connection_config` variable:

```sh
'host':'localhost',
# 'unix_socket': socket,
```

### Differences Noticed

DB selects data into OUTFILE and then LOADs data INFILE in the defined chunks. Finally it does checksumming based on queries like these:

```sql
2018-04-03T04:09:23.520806Z       77 Query    /* /usr/local/bin/osc_cli:db.pyc */ SELECT  count(*) as cnt, bit_xor(crc32(@range_end_0:=`id`)), bit_xor(crc32(`name`)), bit_xor(crc32(`email`)), bit_xor(crc32(`active`)), bit_xor(crc32(`active_woi`)), bit_xor(crc32(`bambam5`)), bit_xor(crc32(`bambam6`)), bit_xor(crc32(`booboo5`)) FROM (  SELECT * FROM `__osc_new_users` FORCE INDEX (`PRIMARY`)  WHERE ( `id` > @range_start_0 )  ORDER BY `id` LIMIT 64935 ) as tmp
```

PT does simple insert into select and doesn't execute any specific query for checksumming. Might be happening inside their code but nothing mentioned in the doc, command's output or general log.

```
18-04-03T04:19:18.231881Z       81 Query    EXPLAIN SELECT `id`, `name`, `email`, `active`, `active_woi`, `bambam5`, `bambam6`, `booboo5` FROM `experiments`.`users` FORCE INDEX(`PRIMARY`) WHERE ((`id` >= '29798504')) AND ((`id` <= '29854092')) LOCK IN SHARE MODE /*explain pt-online-schema-change 30864 copy nibble*/
2018-04-03T04:19:18.232317Z       81 Query    INSERT LOW_PRIORITY IGNORE INTO `experiments`.`_users_new` (`id`, `name`, `email`, `active`, `active_woi`, `bambam5`, `bambam6`, `booboo5`) SELECT `id`, `name`, `email`, `active`, `active_woi`, `bambam5`, `bambam6`, `booboo5` FROM `experiments`.`users` FORCE INDEX(`PRIMARY`) WHERE ((`id` >= '29798504')) AND ((`id` <= '29854092')) LOCK IN SHARE MODE /*pt-online-schema-change 30864 copy nibble*/
```