**Comment from Launchpad by: Daniel Nichter on: 14-12-2013 03:39:45

1) use insert ... ON DUPLICATE KEY UPDATE col1=VALUES(col1), col2=VALUES(col2), ...

Not possible, too complex and dangerous to change this tool.

2) "set FOREIGN_KEY_CHECKS=0" should always be set.

I think that's a good idea for the next major version of this tool, but for backwards compat, I've left --[no]foreign-key-checks to the same default: yes (i.e on)

3) if a table does have "foreign key constraints with C<ON DELETE> or C<ON UPDATE> definitions" don't allow sync to execute without "set FOREIGN_KEY_CHECKS=0". i.e. if throw an error and say how to do safely

I've done this: --[no]check-child-tables, default: yes. It can be disabled with --no-check-child-tables, and then you probably also want to --no-foreign-key-checks, as noted in the docs for --[no]check-child-tables.

For the current version of this tool, I think this will go a long way: it will at least keep users from unknowingly truncating child tables, but it's still backwards compat. In the next major version of pt-table-sync we can set new/different defaults.

**Comment from Launchpad by: Ryan Huddleston on: 17-09-2013 04:38:40

3) if a table does have "foreign key constraints with C<ON DELETE> or C<ON UPDATE> definitions" don't allow sync to execute without "set FOREIGN_KEY_CHECKS=0". i.e. if throw an error and say how to do safely

**Comment from Launchpad by: Ryan Huddleston on: 17-09-2013 04:34:37

I'm thinking two changes may make sense:

1) use insert ... ON DUPLICATE KEY UPDATE col1=VALUES(col1), col2=VALUES(col2), ...
2) seems "set FOREIGN_KEY_CHECKS=0" should always be set. The goal is to not change the master just replicate what is already there

**Comment from Launchpad by: Daniel Nichter on: 10-09-2013 16:58:20

This is, however, documented (in the OUTPUT section however--should be more prominent):

"""
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.
"""