``pt-online-schema-change`` could break replication.

**Reported in Launchpad by gu lei last update 19-03-2012 16:57:32

pt-online-schema-change h=127.0.0.1,P=3306,t=db.tiny_url --alter "drop key url","add key url(url(80))" --sleep 0.1

MySQL version:5.1.55-rel12.6-log Percona Server with XtraDB (GPL), Release 12.6, Revision 200

on slave:

show slave status\G

Master_Host: 192.168.1.1
Master_User: repuser
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: crtalk1-bin.009260
Read_Master_Log_Pos: 125939386
Relay_Log_File: tw_usr-relay-bin.029288
Relay_Log_Pos: 122264451
Relay_Master_Log_File: crtalk1-bin.009260
Slave_IO_Running: Yes
Slave_SQL_Running: No
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 1146
Last_Error: Error 'Table 'db.__tmp_tiny_url' doesn't exist' on opening tables
Skip_Counter: 0
Exec_Master_Log_Pos: 122264304
Relay_Log_Space: 125939734
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 1146
Last_SQL_Error: Error 'Table 'db.__tmp_tiny_url' doesn't exist' on opening tables

binlog on master:
mysqlbinlog -v -v --base64-output=DECODE-ROWS crtalk1-bin.009261 | grep -B 1 -A 10 __tmp|more
#120216 0:00:27 server id 152233306 end_log_pos 29260 Table_map: `db`.`tiny_url` mapp
ed to number 278651
#120216 0:00:27 server id 152233306 end_log_pos 29324 Table_map: `db`.`__tmp_tiny_url
` mapped to number 278645
#120216 0:00:27 server id 152233306 end_log_pos 29420 Write_rows: table id 278651
#120216 0:00:27 server id 152233306 end_log_pos 29516 Write_rows: table id 278645 flags: S
TMT_END_F

1. 1. 1. INSERT INTO db.tiny_url
      2. SET
      3. @1=88801080 /* INT meta=0 nullable=0 is_null=0 */
      4. @2='http://15449413.blog.hexun.com/62026240_d.html' /* VARSTRING(400) meta=400 nullable=0 is_n
         ull=0 */
      5. @3='--' /* VARSTRING(18) meta=18 nullable=0 is_null=0 */
      6. @4=0 /* LONGINT meta=0 nullable=0 is_null=0 */
      7. @5='00:00:27' /* TIME meta=0 nullable=0 is_null=0 */
      8. INSERT INTO db.__tmp_tiny_url
      9. SET
      10. @1=88801080 /* INT meta=0 nullable=0 is_null=0 */
      11. @2='http://15449413.blog.hexun.com/62026240_d.html' /* VARSTRING(400) meta=400 nullable=0 is_n
          ull=0 */
      12. @3='--' /* VARSTRING(18) meta=18 nullable=0 is_null=0 */
      13. @4=0 /* LONGINT meta=0 nullable=0 is_null=0 */
      14. @5='00:00:27' /* TIME meta=0 nullable=0 is_null=0 */
2. at 29516
   #120216 0:00:27 server id 152233306 end_log_pos 29543 Xid = 38657832443
   COMMIT/!/;
3. at 29543

__tmp_tiny_url created only on master but triggers wrote binlog so error occured on slave.