Add and test --[no]check-child-tables.

bin/pt-table-sync

@@ -10943,6 +10943,27 @@ sub ok_to_sync {
       }
    }
 
+   my $replace = $o->get('replace')
+              || $o->get('replicate')
+              || $o->get('sync-to-master');
+   if ( $replace && $o->get('execute') && $o->get('check-child-tables') ) {
+      my $child_tables = find_child_tables(
+         tbl    => $src,
+         dbh    => $src->{dbh},
+         Quoter => $q,
+      );
+      if ( $child_tables ) {
+         foreach my $tbl ( @$child_tables ) {
+            my $ddl = $tp->get_create_table(
+               $src->{dbh}, $tbl->{db}, $tbl->{tbl});
+            if ( $ddl && $ddl =~ m/(ON (?:DELETE|UPDATE) (?:SET|CASCADE))/ ) {
+               my $fk = $1;
+               die "REPLACE statements on $src->{db}.$src->{tbl} can adversely affect child table $tbl->{name} because it has an $fk foreign key constraint.  See --[no]check-child-tables in the documentation for more information.  --check-child-tables error\n"
+            }
+         }
+      }
+   }
+
    return;
 }
 
@@ -11363,6 +11384,46 @@ sub diff_where {
 }
 }
 
+sub find_child_tables {
+   my ( %args ) = @_;
+   my @required_args = qw(tbl dbh Quoter);
+   foreach my $arg ( @required_args ) {
+      die "I need a $arg argument" unless $args{$arg};
+   }
+   my ($tbl, $dbh, $q) = @args{@required_args};
+
+   if ( lc($tbl->{tbl_struct}->{engine} || '') eq 'myisam' ) {
+      PTDEBUG && _d(q{MyISAM table, not looking for child tables});
+      return;
+   }
+
+   PTDEBUG && _d('Finding child tables');
+
+   my $sql = "SELECT table_schema, table_name "
+           . "FROM information_schema.key_column_usage "
+           . "WHERE constraint_schema='$tbl->{db}' "
+           . "AND referenced_table_name='$tbl->{tbl}'";
+   PTDEBUG && _d($sql);
+   my $rows = $dbh->selectall_arrayref($sql);
+   if ( !$rows || !@$rows ) {
+      PTDEBUG && _d('No child tables found');
+      return;
+   }
+
+   my @child_tables;
+   foreach my $row ( @$rows ) {
+      my $tbl = {
+         db   => $row->[0],
+         tbl  => $row->[1],
+         name => $q->quote(@$row),
+      };
+      push @child_tables, $tbl;
+   }
+
+   PTDEBUG && _d('Child tables:', Dumper(\@child_tables));
+   return \@child_tables;
+}
+
 sub _d {
    my ($package, undef, $line) = caller 0;
    @_ = map { (my $temp = $_) =~ s/\n/\n# /g; $temp; }
@@ -11589,7 +11650,7 @@ L<"SYNOPSIS"> for the overview of the correct usage.
 
 Also be careful with tables that have foreign key constraints with C<ON DELETE>
 or C<ON UPDATE> definitions because these might cause unintended changes on the
-child tables.
+child tables.  See L<"--[no]check-child-tables">.
 
 In general, this tool is best suited when your tables have a primary key or
 unique index.  Although it can synchronize data in tables lacking a primary key
@@ -11875,6 +11936,27 @@ runs SET NAMES UTF8 after connecting to MySQL.  Any other value sets
 binmode on STDOUT without the utf8 layer, and runs SET NAMES after
 connecting to MySQL.
 
+=item --[no]check-child-tables
+
+default: yes
+
+Check if L<"--execute"> will adversely affect child tables.  When
+L<"--replace">, L<"--replicate">, or L<"--sync-to-master"> is specified,
+the tool may sync tables using C<REPLACE> statements.  If a table being
+synced has child tables with C<ON DELETE CASCADE>, C<ON UPDATE CASCADE>,
+or C<ON UPDATE SET NULL>, the tool prints an error and skips the table because
+C<REPLACE> becomes C<DELETE> then C<INSERT>, so the C<DELETE> will cascade
+to the child table and delete its rows.  In the worst case, this can delete
+all rows in child tables!
+
+Specify C<--no-check-child-tables> to disable this check.  To completely
+avoid affecting child tables, also specify C<--no-foreign-key-checks>
+so MySQL will not cascade any operations from the parent to child tables.
+
+This check is only preformed if L<"--execute"> and one of L<"--replace">,
+L<"--replicate">, or L<"--sync-to-master"> is specified.  L<"--print">
+does not check child tables.
+
 =item --[no]check-master
 
 default: yes

t/pt-table-sync/basics.t

@@ -182,7 +182,7 @@ $output = output(
    sub {
       pt_table_sync::main('h=127.1,P=12345,u=msandbox,p=msandbox',
          qw(--print --execute --replicate percona.checksums),
-         qw(--no-foreign-key-checks))
+         qw(--no-foreign-key-checks --no-check-child-tables))
    }
 );
 

t/pt-table-sync/safety_checks.t

@@ -0,0 +1,88 @@
+#!/usr/bin/env perl
+
+BEGIN {
+   die "The PERCONA_TOOLKIT_BRANCH environment variable is not set.\n"
+      unless $ENV{PERCONA_TOOLKIT_BRANCH} && -d $ENV{PERCONA_TOOLKIT_BRANCH};
+   unshift @INC, "$ENV{PERCONA_TOOLKIT_BRANCH}/lib";
+};
+
+use strict;
+use warnings FATAL => 'all';
+use English qw(-no_match_vars);
+use Test::More;
+use Data::Dumper;
+
+use PerconaTest;
+use Sandbox;
+require "$trunk/bin/pt-table-sync";
+
+my $output;
+my $dp = new DSNParser(opts=>$dsn_opts);
+my $sb = new Sandbox(basedir => '/tmp', DSNParser => $dp);
+my $master_dbh = $sb->get_dbh_for('master');
+my $slave_dbh  = $sb->get_dbh_for('slave1');
+
+if ( !$master_dbh ) {
+   plan skip_all => 'Cannot connect to sandbox master';
+}
+elsif ( !$slave_dbh ) {
+   plan skip_all => 'Cannot connect to sandbox slave';
+}
+
+my $master_dsn = $sb->dsn_for('master');
+my $slave1_dsn = $sb->dsn_for('slave1');
+
+# #############################################################################
+# --[no]check-child-tables
+# pt-table-sync deletes child table rows Edit
+# https://bugs.launchpad.net/percona-toolkit/+bug/1223458
+# #############################################################################
+
+$sb->load_file('master', 't/pt-table-sync/samples/on_del_cas.sql');
+
+$master_dbh->do("INSERT INTO on_del_cas.parent VALUES (1), (2)");
+$master_dbh->do("INSERT INTO on_del_cas.child1 VALUES (null, 1)");
+$master_dbh->do("INSERT INTO on_del_cas.child2 VALUES (null, 1)");
+$sb->wait_for_slaves();
+
+$output = output(
+   sub {
+      pt_table_sync::main($slave1_dsn, qw(--sync-to-master),
+         qw(--execute -d on_del_cas))
+   },
+   stderr => 1,
+);
+
+like(
+   $output,
+   qr/on on_del_cas.parent can adversely affect child table `on_del_cas`.`child2` because it has an ON DELETE CASCADE/,
+   "check-child-tables: error message"
+);
+
+my $rows = $slave_dbh->selectall_arrayref("select * from on_del_cas.child2");
+is_deeply(
+   $rows,
+   [ [1,1] ],
+   "check-child-tables: child2 row not deleted"
+) or diag(Dumper($rows));
+
+$output = output(
+   sub {
+      pt_table_sync::main($slave1_dsn, qw(--sync-to-master),
+         qw(--print -d on_del_cas))
+   },
+   stderr => 1,
+);
+
+unlike(
+   $output,
+   qr/on on_del_cas.parent can adversely affect child table `on_del_cas`.`child2` because it has an ON DELETE CASCADE/,
+   "check-child-tables: no error message with --print"
+);
+
+# #############################################################################
+# Done.
+# #############################################################################
+$sb->wipe_clean($master_dbh);
+ok($sb->ok(), "Sandbox servers") or BAIL_OUT(__FILE__ . " broke the sandbox");
+done_testing;

t/pt-table-sync/samples/on_del_cas.sql

@@ -0,0 +1,19 @@
+DROP DATABASE IF EXISTS on_del_cas;
+CREATE DATABASE on_del_cas;
+USE on_del_cas;
+
+CREATE TABLE parent (
+  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
+) ENGINE=InnoDB;
+
+CREATE TABLE child1 (
+  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  parent_id INT NOT NULL,
+  FOREIGN KEY fk1 (parent_id) REFERENCES parent (id) ON DELETE RESTRICT
+) ENGINE=InnoDB;
+
+CREATE TABLE child2 (
+  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  parent_id INT NOT NULL,
+  FOREIGN KEY fk1 (parent_id) REFERENCES parent (id) ON DELETE CASCADE
+) ENGINE=InnoDB;