Add --default-engine to pt-osc.

bin/pt-online-schema-change

@@ -8461,6 +8461,9 @@ sub create_new_table{
       my $sql    = $ddl;
       $sql       =~ s/\ACREATE TABLE .*?\($/CREATE TABLE $quoted (/m;
       $sql       =~ s/^  CONSTRAINT `/  CONSTRAINT `_/gm;
+      if ( $o->get('default-engine') ) {
+         $sql =~ s/\s+ENGINE=\S+//;
+      }
       PTDEBUG && _d($sql);
       eval {
          $cxn->dbh()->do($sql);
@@ -9619,6 +9622,17 @@ single value of Threads_running that is wrong for every server, but a default of
 50 seems likely to be unacceptably high for most servers, indicating that the
 operation should be canceled immediately.
 
+=item --default-engine
+
+Remove C<ENGINE> from the new table.
+
+By default the new table is created with the same table options as
+the original table, so if the original table uses InnoDB, then the new
+table will use InnoDB.  In certain cases involving replication, this may
+cause unintended changes on replicas which use a different engine for
+the same table.  Specifying this option causes the new table to be
+created with the system's default engine.
+
 =item --defaults-file
 
 short form: -F; type: string

t/pt-online-schema-change/basics.t

@@ -634,6 +634,31 @@ test_alter_table(
                   qw(--no-drop-new-table)],
 );
 
+# #############################################################################
+# --default-engine
+# #############################################################################
+
+SKIP: {
+   skip "--default-engine tests require < MySQL 5.5", 1
+      if $sandbox_version ge '5.5';
+
+   # The alter doesn't actually change the engine (test_type),
+   # but the --default-engine does because the table uses InnoDB
+   # but MyISAM is the default engine before MySQL 5.5.
+   test_alter_table(
+      name       => "--default-engine",
+      table      => "pt_osc.t",
+      file       => "default-engine.sql",
+      test_type  => "new_engine",
+      new_engine => "MyISAM",
+      cmds       => [
+         '--default-engine',
+         '--execute',
+         '--alter', 'ADD INDEX (d)',
+      ],
+   );
+}
+
 # #############################################################################
 # Done.
 # #############################################################################

t/pt-online-schema-change/samples/default-engine.sql

@@ -0,0 +1,20 @@
+DROP DATABASE IF EXISTS pt_osc;
+CREATE DATABASE pt_osc;
+USE pt_osc;
+CREATE TABLE t (
+  id int auto_increment primary key,
+  c  char(32),
+  d  date,
+  unique index (c(32))
+) ENGINE=InnoDB;
+INSERT INTO pt_osc.t VALUES
+   (null, 'a', now()),
+   (null, 'b', now()),
+   (null, 'c', now()),
+   (null, 'd', now()),
+   (null, 'e', now()),
+   (null, 'f', now()),
+   (null, 'g', now()),
+   (null, 'h', now()),
+   (null, 'i', now()),
+   (null, 'j', now()); -- 10