advice on pt-online-schema-change--cause dead lock

[wayuki]

I am a DBA @China,pt-online-schema-change is a great tool,
in online ddl,for update,the trigger is

 my $update_trigger
      = "CREATE TRIGGER `${prefix}_upd` AFTER UPDATE ON $orig_tbl->{name} "
      . "FOR EACH ROW "
      . "BEGIN "
      . "DELETE IGNORE FROM $new_tbl->{name} WHERE !($upd_index_cols) AND $del_index_cols;"
      . "REPLACE INTO $new_tbl->{name} ($qcols) VALUES ($new_vals);"
      . "END ";

if there is a unique key at second index,sush as
CREATE TABLE `myitem` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT ,
  `mer_item_no` bigint(20) unsigned NOT NULL DEFAULT '0' , PRIMARY KEY (`id`),
  UNIQUE KEY `uni_merchandise_item` (`mer_item_no`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8
it can cause gap lock,why not change to just

​insert into on duplicate key update

no delete from,
then no gap lock ,since gap lock can cause many deadlock

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PT-1427