File Coverage

blib/lib/DBIx/OnlineDDL.pm

Criterion	Covered	Total	%
statement	364	493	73.8
branch	43	136	31.6
condition	32	120	26.6
subroutine	43	56	76.7
pod	11	12	91.6
total	493	817	60.3

package DBIx::OnlineDDL;

our $AUTHORITY = 'cpan:GSG';
# ABSTRACT: Run DDL on online databases safely
use version;
our $VERSION = 'v0.930.1'; # VERSION

use v5.10;
use Moo;
use MooX::StrictConstructor;

use Types::Standard        qw( Str Bool HashRef CodeRef InstanceOf Dict Optional );
use Types::Common::Numeric qw( PositiveNum PositiveInt );

use Class::Load;
use DBI::Const::GetInfoType;
use DBIx::BatchChunker 0.92;  # with stmt attrs
use Eval::Reversible;
use List::Util        1.44 (qw( uniq any all ));  # 1.44 has uniq
use Sub::Util               qw( subname set_subname );
use Term::ProgressBar 2.14;   # with silent option

# Don't export the above, but don't conflict with StrictConstructor, either
use namespace::clean -except => [qw< new meta >];

my $DEFAULT_MAX_ATTEMPTS = 20;

#pod =encoding utf8
#pod
#pod =head1 SYNOPSIS
#pod
#pod     use DBIx::OnlineDDL;
#pod     use DBIx::BatchChunker;
#pod
#pod     DBIx::OnlineDDL->construct_and_execute(
#pod         rsrc          => $dbic_schema->source('Account'),
#pod         ### OR ###
#pod         dbi_connector => $dbix_connector_retry_object,
#pod         table_name    => 'accounts',
#pod
#pod         coderef_hooks => {
#pod             # This is the phase where the DDL is actually run
#pod             before_triggers => \&drop_foobar,
#pod
#pod             # Run other operations right before the swap
#pod             before_swap => \&delete_deprecated_accounts,
#pod         },
#pod
#pod         process_name => 'Dropping foobar from accounts',
#pod
#pod         copy_opts => {
#pod             chunk_size => 5000,
#pod             debug => 1,
#pod         },
#pod     );
#pod
#pod     sub drop_foobar {
#pod         my $oddl  = shift;
#pod         my $name  = $oddl->new_table_name;
#pod         my $qname = $oddl->dbh->quote_identifier($name);
#pod
#pod         # Drop the 'foobar' column, since it is no longer used
#pod         $oddl->dbh_runner_do("ALTER TABLE $qname DROP COLUMN foobar");
#pod     }
#pod
#pod     sub delete_deprecated_accounts {
#pod         my $oddl = shift;
#pod         my $name = $oddl->new_table_name;
#pod         my $dbh  = $oddl->dbh;  # only use for quoting!
#pod
#pod         my $qname = $dbh->quote_identifier($name);
#pod
#pod         DBIx::BatchChunker->construct_and_execute(
#pod             chunk_size  => 5000,
#pod
#pod             debug => 1,
#pod
#pod             process_name     => 'Deleting deprecated accounts',
#pod             process_past_max => 1,
#pod
#pod             dbic_storage => $oddl->rsrc->storage,
#pod             min_stmt => "SELECT MIN(account_id) FROM $qname",
#pod             max_stmt => "SELECT MAX(account_id) FROM $qname",
#pod             stmt     => join("\n",
#pod                 "DELETE FROM $qname",
#pod                 "WHERE",
#pod                 "    account_type = ".$dbh->quote('deprecated')." AND",
#pod                 "    account_id BETWEEN ? AND ?",
#pod             ),
#pod         );
#pod     }
#pod
#pod =head1 DESCRIPTION
#pod
#pod This is a database utility class for running DDL operations (like C) safely
#pod on large tables.  It has a similar scope as L, but is designed for
#pod DDL, rather than DML.  It also has a similar function to other utilities like
#pod L or
#pod L, but actually works properly with foreign
#pod keys, and is written as a Perl module to hook directly into a DBI handle.
#pod
#pod Like most online schema change tools, this works by creating a new shell table that looks
#pod just like the old table, running the DDL changes (through the L hook),
#pod copying data to the new table, and swapping the tables.  Triggers are created to keep the
#pod data in sync.  See L for more information.
#pod
#pod The full operation is protected with an L via L.
#pod If any step in the process fails, the undo stack is run to return the DB back to normal.
#pod
#pod This module uses as many of the DBI info methods as possible, along with ANSI SQL in most
#pod places, to be compatible with multiple RDBMS.  So far, it will work with MySQL or SQLite,
#pod but can be expanded to include more systems with a relatively small amount of code
#pod changes.  (See L for details.)
#pod
#pod B You should not rely on this class to magically fix any and all locking
#pod problems the DB might experience just because it's being used.  Thorough testing and
#pod best practices are still required.
#pod
#pod =head2 When you shouldn't use this module
#pod
#pod =head3 Online DDL is already available in the RDBMS
#pod
#pod If you're running MySQL 5.6+ without clustering, just use C for every DDL
#pod statement.  It is seriously simple and guarantees that the table changes you make are not
#pod going to lock the table, or it will fail right away to tell you it's an incompatible
#pod change.
#pod
#pod If you're running something like Galera clusters, this typically wouldn't be an option,
#pod as it would lock up the clusters while the C statement is running, despite
#pod the C statement.  (Galera clusters were the prime motivation for writing this
#pod module.)
#pod
#pod Other RDBMSs may have support for online DDL as well.  Check the documentation first.  If
#pod they don't, patches for this tool are welcome!
#pod
#pod =head3 The operation is small
#pod
#pod Does your DDL only take 2 seconds?  Just do it!  Don't bother with trying to swap tables
#pod around, wasting time with full table copies, etc.  It's not worth the time spent or risk.
#pod
#pod =head3 When you actually want to run DML, not DDL
#pod
#pod L is more appropriate for running DML operations (like C,
#pod C, C).  If you need to do both, you can use the L hook
#pod for DDL, and the L hook for DML.  Or just run DBIx::BatchChunker after the
#pod OnlineDDL process is complete.
#pod
#pod =head3 Other online schema change tools fit your needs
#pod
#pod Don't have foreign key constraints and C is already working for you?  Great!
#pod Keep using it.
#pod
#pod =head1 ATTRIBUTES
#pod
#pod =head2 DBIC Attributes
#pod
#pod =head3 rsrc
#pod
#pod A L.  This will be the source used for all operations, DDL or
#pod otherwise.  Optional, but recommended for DBIC users.
#pod
#pod The DBIC storage handler's C will be tweaked to ensure sane defaults and
#pod proper post-connection details.
#pod
#pod =cut

has rsrc => (
    is       => 'ro',
    isa      => InstanceOf['DBIx::Class::ResultSource'],
    required => 0,
);

#pod =head3 dbic_retry_opts
#pod
#pod A hashref of DBIC retry options.  These options control how retry protection works within
#pod DBIC.  Right now, this is just limited to C, which controls the number of
#pod times to retry.  The default C is 20.
#pod
#pod =cut

has dbic_retry_opts => (
    is       => 'ro',
    isa      => HashRef,
    required => 0,
    default  => sub { {} },
);

#pod =head2 DBI Attributes
#pod
#pod =head3 dbi_connector
#pod
#pod A L object.  Instead of L statement handles, this is the
#pod recommended non-DBIC way for OnlineDDL (and BatchChunker) to interface with the DBI, as
#pod it handles retries on failures.  The connection mode used is whatever default is set
#pod within the object.
#pod
#pod Required, except for DBIC users, who should be setting L above.  It is also
#pod assumed that the correct database is already active.
#pod
#pod The object will be tweaked to ensure sane defaults, proper post-connection details, a
#pod custom C, and set a default C of 20, if not already set.
#pod
#pod =cut

has dbi_connector => (
    is       => 'ro',
    isa      => InstanceOf['DBIx::Connector::Retry'],
    required => 0,
);

#pod =head3 table_name
#pod
#pod The table name to be copied and eventually replaced.  Required unless L is
#pod specified.
#pod
#pod =cut

has table_name => (
    is       => 'ro',
    isa      => Str,
    required => 1,
    lazy     => 1,
    default  => sub {
        my $rsrc = shift->rsrc // return;
        $rsrc->from;
    },
);

#pod =head3 new_table_name
#pod
#pod The new table name to be created, copied to, and eventually used as the final table.
#pod Optional.
#pod
#pod If not defined, a name will be created automatically.  This might be the better route,
#pod since the default builder will search for an unused name in the DB right before OnlineDDL
#pod needs it.
#pod
#pod =cut

has new_table_name => (
    is       => 'ro',
    isa      => Str,
    required => 0,
    lazy     => 1,
    builder  => 1,
);

sub _build_new_table_name {
    my $self = shift;
    my $dbh  = $self->dbh;
    my $vars = $self->_vars;

    my $catalog         = $vars->{catalog};
    my $schema          = $vars->{schema};
    my $orig_table_name = $self->table_name;

    my $escape = $dbh->get_info( $GetInfoType{SQL_SEARCH_PATTERN_ESCAPE} ) // '\\';

    return $self->_find_new_identifier(
        "_${orig_table_name}_new" => set_subname('_new_table_name_finder', sub {
            $dbh = shift;
            my $like_expr = shift;
            $like_expr =~ s/([_%])/$escape$1/g;

            $dbh->table_info($catalog, $schema, $like_expr)->fetchrow_array;
        }),
        'SQL_MAXIMUM_TABLE_NAME_LENGTH',
    );
}

#pod =head2 Progress Bar Attributes
#pod
#pod =head3 progress_bar
#pod
#pod The progress bar used for most of the process.  A different one is used for the actual
#pod table copy with L, since that step takes longer.
#pod
#pod Optional.  If the progress bar isn't specified, a default one will be created.  If the
#pod terminal isn't interactive, the default L will be set to C to
#pod naturally skip the output.
#pod
#pod =cut

has progress_bar => (
    is       => 'rw',
    isa      => InstanceOf['Term::ProgressBar'],
);

sub _progress_bar_setup {
    my $self = shift;
    my $vars = $self->_vars;

    my $steps = 6 + scalar keys %{ $self->coderef_hooks };

    my $progress = $self->progress_bar || Term::ProgressBar->new({
        name   => $self->progress_name,
        count  => $steps,
        ETA    => 'linear',
        silent => !(-t *STDERR && -t *STDIN),  # STDERR is what {fh} is set to use
    });

    $vars->{progress_bar} = $progress;
}

#pod =head3 progress_name
#pod
#pod A string used to assist in creating a progress bar.  Ignored if L is
#pod already specified.
#pod
#pod This is the preferred way of customizing the progress bar without having to create one
#pod from scratch.
#pod
#pod =cut

has progress_name => (
    is       => 'rw',
    isa      => Str,
    required => 0,
    lazy     => 1,
    default  => sub {
        my $table_name = shift->table_name;
        'Altering'.($table_name ? " $table_name" : '');
    },
);

#pod =head2 Other Attributes
#pod
#pod =head3 coderef_hooks
#pod
#pod A hashref of coderefs.  Each of these are used in different steps in the process.  All
#pod of these are optional, but it is B that C is
#pod specified.  Otherwise, you're not actually running any DDL and the table copy is
#pod essentially a no-op.
#pod
#pod All of these triggers pass the C object as the only argument.  The
#pod L can be acquired from that and used in SQL statements.  The L
#pod and L methods should be used to protect against disconnections or locks.
#pod
#pod There is room to add more hooks here, but only if there's a good reason to do so.
#pod (Running the wrong kind of SQL at the wrong time could be dangerous.)  Create a GitHub
#pod issue if you can think of one.
#pod
#pod =head4 before_triggers
#pod
#pod This is called before the table triggers are applied.  Your DDL should take place here,
#pod for a few reasons:
#pod
#pod     1. The table is empty, so DDL should take no time at all now.
#pod
#pod     2. After this hook, the table is reanalyzed to make sure it has an accurate picture
#pod     of the new columns.  This is critical for the creation of the triggers.
#pod
#pod =head4 before_swap
#pod
#pod This is called after the new table has been analyzed, but before the big table swap.  This
#pod hook might be used if a large DML operation needs to be done while the new table is still
#pod available.  If you use this hook, it's highly recommended that you use something like
#pod L to make sure the changes are made in a safe and batched manner.
#pod
#pod =cut

has coderef_hooks => (
    is       => 'ro',
    isa      => Dict[
        before_triggers => Optional[CodeRef],
        before_swap     => Optional[CodeRef],
    ],
    required => 0,
    default  => sub { +{} },
);

#pod =head3 copy_opts
#pod
#pod A hashref of different options to pass to L, which is used in the
#pod L step.  Some of these are defined automatically.  It's recommended that you
#pod specify at least these options:
#pod
#pod     chunk_size  => 5000,     # or whatever is a reasonable size for that table
#pod     id_name     => 'pk_id',  # especially if there isn't an obvious integer PK
#pod
#pod Specifying L is not recommended, since Active DBI Processing
#pod mode will be used.
#pod
#pod These options will be included into the hashref, unless specifically overridden by key
#pod name:
#pod
#pod     id_name      => $first_pk_column,  # will warn if the PK is multi-column
#pod     target_time  => 1,
#pod     sleep        => 0.5,
#pod
#pod     # If using DBIC
#pod     dbic_storage => $rsrc->storage,
#pod     rsc          => $id_rsc,
#pod     dbic_retry_opts => {
#pod         max_attempts  => 20,
#pod         # best not to change this, unless you know what you're doing
#pod         retry_handler => $onlineddl_retry_handler,
#pod     },
#pod
#pod     # If using DBI
#pod     dbi_connector => $oddl->dbi_connector,
#pod     min_stmt      => $min_sql,
#pod     max_stmt      => $max_sql,
#pod
#pod     # For both
#pod     count_stmt    => $count_sql,
#pod     stmt          => $insert_select_sql,
#pod     progress_name => $copying_msg,
#pod
#pod =cut

has copy_opts => (
    is       => 'ro',
    isa      => HashRef,
    required => 0,
    lazy     => 1,
    default  => sub { {} },
);

# This is filled in during copy_rows, since the _column_list call needs to happen after
# the DDL has run.
sub _fill_copy_opts {
    my $self = shift;
    my $rsrc = $self->rsrc;
    my $dbh  = $self->dbh;
    my $vars = $self->_vars;

    my $copy_opts = $self->copy_opts;
    my $helper    = $self->_helper;

    my $catalog         = $vars->{catalog};
    my $schema          = $vars->{schema};
    my $orig_table_name = $self->table_name;
    my $new_table_name  = $self->new_table_name;

    my $orig_table_name_quote = $dbh->quote_identifier($orig_table_name);
    my $new_table_name_quote  = $dbh->quote_identifier($new_table_name);

    # Sane defaults for timing
    $copy_opts->{target_time} //= 1;
    # Copies create lots of rapid I/O, binlog generation, etc. on the primary.
    # Some sleep time gives other servers a chance to catch up:
    $copy_opts->{sleep}       //= 0.5;

    # Figure out what the id_name is going to be
    my $id_name = $copy_opts->{id_name} //= $self->dbh_runner(run => set_subname '_pk_finder', sub {
        $dbh = $_;
        my @ids = $dbh->primary_key($catalog, $schema, $orig_table_name);

        die  "No primary key found for $orig_table_name"                                 unless @ids;
        warn "Using the first column of a multi-column primary key for $orig_table_name" if @ids > 1;

        $ids[0];
    });

    my $id_name_quote = $dbh->quote_identifier($id_name);

    if ($rsrc) {
        $copy_opts->{dbic_storage} //= $rsrc->storage;
        $copy_opts->{rsc} //= $rsrc->resultset->get_column($id_name);

        $copy_opts->{dbic_retry_opts} //= {};
        $copy_opts->{dbic_retry_opts}{max_attempts}  //= $DEFAULT_MAX_ATTEMPTS;
        $copy_opts->{dbic_retry_opts}{retry_handler}   = sub { $self->_retry_handler(@_) };
    }
    else {
        $copy_opts->{dbi_connector} //= $self->dbi_connector;
        $copy_opts->{min_stmt} //= "SELECT MIN($id_name_quote) FROM $orig_table_name_quote";
        $copy_opts->{max_stmt} //= "SELECT MAX($id_name_quote) FROM $orig_table_name_quote";
    }

    my @column_list = $self->_column_list;
    my $column_list_str = join(', ', map { $dbh->quote_identifier($_) } @column_list );

    # The INSERT..SELECT is a bit different depending on the RDBMS used, mostly because
    # of the IGNORE part
    my $insert_select_stmt = $helper->insert_select_stmt($column_list_str);

    $copy_opts->{count_stmt} //= "SELECT COUNT(*) FROM $orig_table_name_quote WHERE $id_name_quote BETWEEN ? AND ?";
    $copy_opts->{stmt}       //= $insert_select_stmt;

    $copy_opts->{progress_name} //= "Copying $orig_table_name" unless $copy_opts->{progress_bar};

    return $copy_opts;
}

#pod =head3 db_timeouts
#pod
#pod A hashref of timeouts used for various DB operations, and usually set at the beginning of
#pod each connection.  Some of these settings may be RDBMS-specific.
#pod
#pod =head4 lock_file
#pod
#pod Amount of time (in seconds) to wait when attempting to acquire filesystem locks (on
#pod filesystems which support locking).  Float or fractional values are allowed.  This
#pod currently only applies to SQLite.
#pod
#pod Default value is 1 second.  The downside is that the SQLite default is actually 0, so
#pod other (non-OnlineDDL) connections should have a setting that is more than that to prevent
#pod lock contention.
#pod
#pod =head4 lock_db
#pod
#pod Amount of time (in whole seconds) to wait when attempting to acquire table and/or database
#pod level locks before falling back to retry.
#pod
#pod Default value is 60 seconds.
#pod
#pod =head4 lock_row
#pod
#pod Amount of time (in whole seconds) to wait when attempting to acquire row-level locks,
#pod which apply to much lower-level operations than L.  At this scope, the lesser
#pod of either of these two settings will take precedence.
#pod
#pod Default value is 2 seconds.  Lower values are preferred for row lock wait timeouts, so
#pod that OnlineDDL is more likely to be the victim of lock contention.  OnlineDDL can simply
#pod retry the connection at that point.
#pod
#pod =head4 session
#pod
#pod Amount of time (in whole seconds) for inactive session timeouts on the database side.
#pod
#pod Default value is 28,800 seconds (8 hours), which is MySQL's default.
#pod
#pod =cut

has db_timeouts => (
    is       => 'ro',
    isa      => Dict[
        lock_file => Optional[PositiveNum],
        lock_db   => Optional[PositiveInt],
        lock_row  => Optional[PositiveInt],
        session   => Optional[PositiveInt],
    ],
    required => 0,
);

#pod =head3 reversible
#pod
#pod A L object, used for rollbacks.  A default will be created, if not
#pod specified.
#pod
#pod =cut

has reversible => (
    is       => 'rw',
    isa      => InstanceOf['Eval::Reversible'],
    required => 1,
    lazy     => 1,
    default  => sub { Eval::Reversible->new },
);

### Private attributes

has _vars => (
    is       => 'rw',
    isa      => HashRef,
    required => 0,
    init_arg => undef,
    lazy     => 1,
    default  => sub { {} },
);

has _helper => (
    is       => 'ro',
    isa      => InstanceOf['DBIx::OnlineDDL::Helper::Base'],
    required => 0,
    init_arg => undef,
    lazy     => 1,
    builder  => '_build_helper',
);

sub _build_helper {
    my $self = shift;

    my $dbh = $self->dbh;

    # Get and store the DBMS_NAME.  This is not the lowercase driver name (ie: mysql),
    # unless the {Driver}{Name} alternative wins out.
    my $dbms_name = $self->_vars->{dbms_name} = $dbh->get_info( $GetInfoType{SQL_DBMS_NAME} ) // $dbh->{Driver}->{Name};

    my $helper_class = "DBIx::OnlineDDL::Helper::$dbms_name";

    # Die if we can't load the RDBMS-specific class, since there's a lot of gaps in Base
    die "OnlineDDL is not designed for $dbms_name systems yet!" unless Class::Load::load_optional_class($helper_class);

    return $helper_class->new( online_ddl => $self );
}

### BUILD methods

around BUILDARGS => sub {
    my $next  = shift;
    my $class = shift;

    my %args = @_ == 1 ? %{ $_[0] } : @_;

    # Quick sanity checks
    die 'A DBIC ResultSource (rsrc) or DBIx::Connector::Retry object (dbi_connector) is required' unless (
        $args{rsrc} || $args{dbi_connector}
    );

    # Defaults for db_timeouts (see POD above).  We set these here, because each
    # individual timeout should be checked to see if it's defined.
    $args{db_timeouts} //= {};
    $args{db_timeouts}{lock_file} //= 1;
    $args{db_timeouts}{lock_db}   //= 60;
    $args{db_timeouts}{lock_row}  //= 2;
    $args{db_timeouts}{session}   //= 28_800;

    $class->$next( %args );
};

sub BUILD {
    my $self = shift;
    my $rsrc = $self->rsrc;

    my $dbh    = $self->dbh;
    my $helper = $self->_helper;

    # Get the current catalog/schema
    my ($catalog, $schema) = $helper->current_catalog_schema;

    $self->_vars->{catalog} = $catalog;
    $self->_vars->{schema}  = $schema;

    # Add in the post-connection details
    my @stmts = $helper->post_connection_stmts;

    if ($rsrc) {
        ### DBIC Storage

        my @post_connection_details = map { [ do_sql => $_ ] } @stmts;

        # XXX: Tapping into a private attribute here, but it's a lot better than parsing
        # $storage->connect_info.  We are also not attaching these details to
        # connect_info, so public introspection won't pick up our changes.  Undecided
        # whether this is good or bad...

        my $storage         = $rsrc->storage;
        my $on_connect_call = $storage->_dbic_connect_attributes->{on_connect_call};

        # Parse on_connect_call to make sure we can add to it
        my $ref = defined $on_connect_call && ref $on_connect_call;
        unless ($on_connect_call) {
            $on_connect_call = \@post_connection_details;
        }
        elsif  (!$ref) {
            $on_connect_call = [ [ do_sql => $on_connect_call ], @post_connection_details ];
        }
        elsif  ($ref eq 'ARRAY') {
            # Double-check that we're not repeating ourselves by inspecting the array for
            # our own statements.
            @$on_connect_call = grep {
                my $e = $_;
                !(  # exclude any of ours
                    $e && ref $e && ref $e eq 'ARRAY' && @$e == 2 &&
                    $e->[0] && !ref $e->[0] && $e->[0] eq 'do_sql' &&
                    $e->[1] && !ref $e->[1] && (any { $e->[1] eq $_ } @stmts)
                );
            } @$on_connect_call;

            my $first_occ = $on_connect_call->[0];
            if ($first_occ && ref $first_occ && ref $first_occ eq 'ARRAY') {
                $on_connect_call = [ @$on_connect_call, @post_connection_details ];
            }
            else {
                $on_connect_call = [ $on_connect_call, @post_connection_details ];
            }
        }
        elsif  ($ref eq 'CODE') {
            $on_connect_call = [ $on_connect_call, @post_connection_details ];
        }
        else {
            die "Illegal reftype $ref for on_connect_call connection attribute!";
        }

        # Set the new options on the relevant attributes that Storage::DBI->connect_info touches.
        $storage->_dbic_connect_attributes->{on_connect_call} = $on_connect_call;
        $storage->on_connect_call($on_connect_call);
    }
    else {
        ### DBIx::Connector::Retry (via DBI Callbacks)

        my $conn      = $self->dbi_connector;
        my $dbi_attrs = $conn->connect_info->[3];

        # Playing with refs, so no need to re-set connect_info
        $conn->connect_info->[3] = $dbi_attrs = {} unless $dbi_attrs;

        # Make sure the basic settings are sane
        $dbi_attrs->{AutoCommit} = 1;
        $dbi_attrs->{RaiseError} = 1;

        # Add the DBI callback
        my $callbacks  = $dbi_attrs->{Callbacks} //= {};
        my $package_re = quotemeta(__PACKAGE__.'::_dbi_connected_callback');

        my $ref = defined $callbacks->{connected} && ref $callbacks->{connected};
        unless ($callbacks->{connected}) {
            $callbacks->{connected} = set_subname '_dbi_connected_callback' => sub {
                shift->do($_) for @stmts;
                return;
            };
        }
        elsif (!$ref || $ref ne 'CODE') {
            die "Illegal reftype $ref for connected DBI Callback!";
        }
        elsif (subname($callbacks->{connected}) =~ /^$package_re/) {  # allow for *_wrapped below
            # This is one of our callbacks; leave it alone!
        }
        else {
            # This is somebody else's callback; wrap around it
            my $old_coderef = $callbacks->{connected};
            $callbacks->{connected} = set_subname '_dbi_connected_callback_wrapped' => sub {
                my $h = shift;
                $old_coderef->($h);
                $h->do($_) for @stmts;
                return;
            };
        }

        # Add a proper retry_handler
        $conn->retry_handler(sub { $self->_retry_handler(@_) });

        # And max_attempts.  XXX: Maybe they actually wanted 10 and not just the default?
        $conn->max_attempts($DEFAULT_MAX_ATTEMPTS) if $conn->max_attempts == 10;
    }

    # Go ahead and run the post-connection statements for this session
    $dbh->{AutoCommit} = 1;
    $dbh->{RaiseError} = 1;
    $dbh->do($_) for @stmts;
}

#pod =head1 CONSTRUCTORS
#pod
#pod See L for information on what can be passed into these constructors.
#pod
#pod =head2 new
#pod
#pod     my $online_ddl = DBIx::OnlineDDL->new(...);
#pod
#pod A standard object constructor. If you use this constructor, you will need to manually
#pod call L to execute the DB changes.
#pod
#pod You'll probably just want to use L.
#pod
#pod =head2 construct_and_execute
#pod
#pod     my $online_ddl = DBIx::OnlineDDL->construct_and_execute(...);
#pod
#pod Constructs a DBIx::OnlineDDL object and automatically calls each method step, including
#pod hooks.  Anything passed to this method will be passed through to the constructor.
#pod
#pod Returns the constructed object, post-execution.  This is typically only useful if you want
#pod to inspect the attributes after the process has finished.  Otherwise, it's safe to just
#pod ignore the return and throw away the object immediately.
#pod
#pod =cut

sub construct_and_execute {
    my $class      = shift;
    my $online_ddl = $class->new(@_);

    $online_ddl->execute;

    return $online_ddl;
}

#pod =head1 METHODS
#pod
#pod =head2 Step Runners
#pod
#pod =head3 execute
#pod
#pod Runs all of the steps as documented in L.  This also includes undo
#pod protection, in case of exceptions.
#pod
#pod =cut

sub execute {
    my $self       = shift;
    my $reversible = $self->reversible;

    $self->_progress_bar_setup;

    $reversible->run_reversibly(set_subname '_execute_part_one', sub {
        $self->create_new_table;
        $self->create_triggers;
        $self->copy_rows;
        $self->swap_tables;
    });
    $reversible->run_reversibly(set_subname '_execute_part_two', sub {
        $self->drop_old_table;
        $self->cleanup_foreign_keys;
    });
}

#pod =head3 fire_hook
#pod
#pod     $online_ddl->fire_hook('before_triggers');
#pod
#pod Fires one of the coderef hooks, if it exists.  This also updates the progress bar.
#pod
#pod See L for more details.
#pod
#pod =cut

sub fire_hook {
    my ($self, $hook_name) = @_;

    my $hooks = $self->coderef_hooks;
    my $vars  = $self->_vars;

    my $progress = $vars->{progress_bar};

    return unless $hooks && $hooks->{$hook_name};

    $progress->message("Firing hook for $hook_name");

    # Fire the hook
    $hooks->{$hook_name}->($self);

    $progress->update;
}

#pod =head2 DBI Helpers
#pod
#pod =head3 dbh
#pod
#pod     $online_ddl->dbh;
#pod
#pod Acquires a database handle, either from L or L.  Not recommended
#pod for active work, as it doesn't offer retry protection.  Instead, use L or
#pod L.
#pod
#pod =cut

sub dbh {
    my $self = shift;

    # Even acquiring a $dbh could die (eg: 'USE $db' or other pre-connect commands), so
    # also try to wrap this in our retry handler.
    my $dbh = $self->dbh_runner( run => sub { $_[0] } );
    return $dbh;
}

#pod =head3 dbh_runner
#pod
#pod     my @items = $online_ddl->dbh_runner(run => sub {
#pod         my $dbh = $_;  # or $_[0]
#pod         $dbh->selectall_array(...);
#pod     });
#pod
#pod Runs the C<$coderef>, locally setting C<$_> to and passing in the database handle.  This
#pod is essentially a shortcut interface into either L or DBIC's L.
#pod
#pod The first argument can either be C or C, which controls whether to wrap the
#pod code in a DB transaction or not.  The return is passed directly back, and return context
#pod is honored.
#pod
#pod =cut

sub _retry_handler {
    my ($self, $runner) = @_;
    my $vars = $self->_vars;

    # NOTE: There's a lot of abusing the fact that BlockRunner and DBIx::Connector::Retry
    # (a la $runner) share similar accessor interfaces.

    my $error        = $runner->last_exception;
    my $is_retryable = $self->_helper->is_error_retryable($error);

    if ($is_retryable) {
        my ($failed, $max) = ($runner->failed_attempt_count, $runner->max_attempts);
        my $progress = $vars->{progress_bar};

        # Warn about the last error
        $progress->message("Encountered a recoverable error: $error") if $progress;

        # Pause for an incremental amount of seconds first, to discourage any future locks
        sleep $failed;

        # If retries are escalating, try forcing a disconnect
        if ($failed >= $max / 2) {
            # Finally have some differences between the two classes...
            if ($runner->isa('DBIx::Class::Storage::BlockRunner')) {
                eval { $runner->storage->disconnect };
            }
            else {
                eval { $runner->disconnect };
            }
        }

        $progress->message( sprintf(
            "Attempt %u of %u", $failed, $max
        ) ) if $progress;
    }

    return $is_retryable;
}

sub dbh_runner {
    my ($self, $method, $coderef) = @_;
    my $wantarray = wantarray;

    die "Only 'txn' or 'run' are acceptable run methods" unless $method =~ /^(?:txn|run)$/;

    my @res;
    if (my $rsrc = $self->rsrc) {
        # No need to load BlockRunner, since DBIC loads it in before us if we're using
        # this method.
        my $block_runner = DBIx::Class::Storage::BlockRunner->new(
            # defaults
            max_attempts => $DEFAULT_MAX_ATTEMPTS,

            # never overrides the important ones below
            %{ $self->dbic_retry_opts },

            retry_handler => sub { $self->_retry_handler(@_) },
            storage  => $rsrc->storage,
            wrap_txn => ($method eq 'txn' ? 1 : 0),
        );

        # This wrapping nonsense is necessary because Try::Tiny within BlockRunner has its own
        # localization of $_.  Fortunately, we can pass arguments to avoid closures.
        my $wrapper = set_subname '_dbh_run_blockrunner_wrapper' => sub {
            my ($s, $c) = @_;
            my $dbh = $s->rsrc->storage->dbh;

            local $_ = $dbh;
            $c->($dbh);  # also pass it in, because that's what DBIx::Connector does
        };

        # BlockRunner can still die post-failure, if $storage->ensure_connected (which calls ping
        # and tries to reconnect) dies.  If that's the case, use our retry handler to check the new
        # error message, and throw it back into BlockRunner.
        my $br_method = 'run';
        while ($block_runner->failed_attempt_count < $block_runner->max_attempts) {
            eval {
                unless (defined $wantarray) {           $block_runner->$br_method($wrapper, $self, $coderef) }
                elsif          ($wantarray) { @res    = $block_runner->$br_method($wrapper, $self, $coderef) }
                else                        { $res[0] = $block_runner->$br_method($wrapper, $self, $coderef) }
            };

            # 'run' resets failed_attempt_count, so subsequent attempts must use
            # '_run', which does not
            $br_method = '_run';

            if (my $err = $@) {
                # Time to really die
                die $err if $err =~ /Reached max_attempts amount of / || $block_runner->failed_attempt_count >= $block_runner->max_attempts;

                # See if the retry handler likes it
                push @{ $block_runner->exception_stack }, $err;
                $block_runner->_set_failed_attempt_count( $block_runner->failed_attempt_count + 1 );
                die $err unless $self->_retry_handler($block_runner);
            }
            else {
                last;
            }
        }
    }
    else {
        my $conn = $self->dbi_connector;
        unless (defined $wantarray) {           $conn->$method($coderef) }
        elsif          ($wantarray) { @res    = $conn->$method($coderef) }
        else                        { $res[0] = $conn->$method($coderef) }
    }

    return $wantarray ? @res : $res[0];
}

#pod =head3 dbh_runner_do
#pod
#pod     $online_ddl->dbh_runner_do(
#pod         "ALTER TABLE $table_name ADD COLUMN foobar",
#pod         ["ALTER TABLE ? DROP COLUMN ?", undef, $table_name, 'baz'],
#pod     );
#pod
#pod Runs a list of commands, encapsulating each of them in a L coderef with calls
#pod to L.  This is handy when you want to run a list of DDL commands, which you don't
#pod care about the output of, but don't want to bundle them into a single non-idempotant
#pod repeatable coderef.  Or if you want to save typing on a single do-able SQL command.
#pod
#pod The items can either be a SQL string or an arrayref of options to pass to L.
#pod
#pod The statement is assumed to be non-transactional.  If you want to run a DB transaction,
#pod you should use L instead.
#pod
#pod =cut

sub dbh_runner_do {
    my ($self, @commands) = @_;

    foreach my $command (@commands) {
        my $ref = ref $command;
        die "$ref references not valid in dbh_runner_do" if $ref && $ref ne 'ARRAY';

        $self->dbh_runner(run => set_subname '_dbh_runner_do', sub {
            $_->do( $ref ? @$command : $command );
        });
    }
}

#pod =head1 STEP METHODS
#pod
#pod You can call these methods individually, but using L instead is
#pod highly recommended.  If you do run these yourself, the exception will need to be caught
#pod and the L undo stack should be run to get the DB back to normal.
#pod
#pod =head2 create_new_table
#pod
#pod Creates the new table, making sure to preserve as much of the original table properties
#pod as possible.
#pod
#pod =cut

sub create_new_table {
    my $self = shift;
    my $dbh  = $self->dbh;
    my $vars = $self->_vars;

    my $progress   = $vars->{progress_bar};
    my $reversible = $self->reversible;
    my $helper     = $self->_helper;

    my $orig_table_name = $self->table_name;
    my $new_table_name  = $self->new_table_name;

    my $orig_table_name_quote = $dbh->quote_identifier($orig_table_name);
    my $new_table_name_quote  = $dbh->quote_identifier($new_table_name);

    # ANSI quotes could also appear in the statement
    my $orig_table_name_ansi_quote = '"'.$orig_table_name.'"';

    $progress->message("Creating new table $new_table_name");

    my $table_sql = $helper->create_table_sql($orig_table_name);
    die "Table $orig_table_name does not exist in the database!" unless $table_sql;

    $table_sql = $helper->rename_fks_in_table_sql($orig_table_name, $table_sql) if $helper->dbms_uses_global_fk_namespace;

    # Change the old->new table name
    my $orig_table_name_quote_re = '('.join('|',
        quotemeta($orig_table_name_quote), quotemeta($orig_table_name_ansi_quote), quotemeta($orig_table_name)
    ).')';
    $table_sql =~ s/(?<=^CREATE TABLE )$orig_table_name_quote_re/$new_table_name_quote/;

    # NOTE: This SQL will still have the old table name in self-referenced FKs.  This is
    # okay, since no supported RDBMS currently auto-renames the referenced table name
    # during table moves, and the old table is still the definitive point-of-record until
    # the table swap.  Furthermore, pointing the FK to the new table may cause bad FK
    # constraint failures within the triggers, if the referenced ID hasn't been copied to
    # the new table yet.
    #
    # If we ever have a RDBMS that does some sort of auto-renaming of FKs, we'll need to
    # accommodate it.  It's also worth noting that turning FKs on during the session can
    # actually affect this kind of behavior.  For example, both MySQL & SQLite will rename
    # them during table swaps, but only if the FK checks are on.

    # Actually create the table
    $self->dbh_runner_do($table_sql);

    # Undo commands, including a failure warning update
    $reversible->failure_warning("\nDropping the new table and rolling back to start!\n\n");
    $reversible->add_undo(sub { $self->dbh_runner_do("DROP TABLE $new_table_name_quote") });

    $progress->update;
}

#pod =head2 create_triggers
#pod
#pod Creates triggers on the original table to make sure any new changes are captured into the
#pod new table.
#pod
#pod =cut

sub create_triggers {
    my $self = shift;
    my $rsrc = $self->rsrc;
    my $dbh  = $self->dbh;
    my $vars = $self->_vars;

    my $progress   = $vars->{progress_bar};
    my $reversible = $self->reversible;
    my $helper     = $self->_helper;

    my $catalog         = $vars->{catalog};
    my $schema          = $vars->{schema};
    my $orig_table_name = $self->table_name;
    my $new_table_name  = $self->new_table_name;

    # Fire the before_triggers hook, which would typically include the DDL
    $self->fire_hook('before_triggers');

    $progress->message("Creating triggers");

    # This shouldn't be cached until now, since the actual DDL may change the column list
    my @column_list = $self->_column_list;

    ### Look for a unique ID set

    # We need to find a proper PK or unique constraint for UPDATE/DELETE triggers.
    # Unlike BatchChunker, we can't just rely on part of a PK.
    my @unique_ids;
    $self->dbh_runner(run => set_subname '_unique_id_finder', sub {
        $dbh = $_;

        my %potential_unique_ids = (
            PRIMARY => [ $dbh->primary_key($catalog, $schema, $orig_table_name) ],
        );

        my $unique_stats = [];
        if ($dbh->can('statistics_info')) {
            # Sometimes, this still dies, even with the 'can' check (eg: older DBD::mysql drivers)
            $unique_stats = eval { $dbh->statistics_info( $catalog, $schema, $orig_table_name, 1, 1 )->fetchall_arrayref({}) };
            $unique_stats = [] if $@;
        }

        foreach my $index_name (uniq map { $_->{INDEX_NAME} } @$unique_stats) {
            my @unique_cols =
                map  { $_->{COLUMN_NAME} }
                sort { $a->{ORDINAL_POSITION} <=> $b->{ORDINAL_POSITION} }
                grep { $_->{INDEX_NAME} eq $index_name && !$_->{NON_UNIQUE} }  # some DBDs might not honor the $unique_only param
                @$unique_stats
            ;
            $potential_unique_ids{$index_name} = \@unique_cols;
        }

        my %column_set = map { $_ => 1 } @column_list;
        foreach my $index_name ('PRIMARY',
            # sort by the number of columns (asc), though PRIMARY still has top priority
            sort { scalar(@{$potential_unique_ids{$a}}) <=> scalar(@{$potential_unique_ids{$b}}) }
            grep { $_ ne 'PRIMARY' }
            keys %potential_unique_ids
        ) {
            my @unique_cols = @{ $potential_unique_ids{$index_name} };
            next unless @unique_cols;

            # Only use this set if all of the columns exist in both tables
            next unless all { $column_set{$_} } @unique_cols;

            @unique_ids = @unique_cols;
        }
    });

    die "Cannot find an appropriate unique index for $orig_table_name!" unless @unique_ids;

    ### Check to make sure existing triggers aren't on the table

    die "Found triggers on $orig_table_name!  Please remove them first, so that our INSERT/UPDATE/DELETE triggers can be applied."
        if $helper->has_triggers_on_table($orig_table_name);

    ### Find a good set of trigger names

    foreach my $trigger_type (qw< INSERT UPDATE DELETE >) {
        my $trigger_name = $helper->find_new_trigger_identifier(
            "${orig_table_name}_onlineddl_".lc($trigger_type)
        );
        $vars->{trigger_names}       {$trigger_type} = $trigger_name;
        $vars->{trigger_names_quoted}{$trigger_type} = $dbh->quote_identifier($trigger_name);
    }

    ### Now create the triggers, with (mostly) ANSI SQL

    my $orig_table_name_quote = $dbh->quote_identifier($orig_table_name);
    my $new_table_name_quote  = $dbh->quote_identifier($new_table_name);

    my $column_list_str     = join(', ', map {        $dbh->quote_identifier($_) } @column_list );
    my $new_column_list_str = join(', ', map { "NEW.".$dbh->quote_identifier($_) } @column_list );

    my $nseo = $helper->null_safe_equals_op;
    my %trigger_dml_stmts;

    # Using REPLACE just in case the row already exists from the copy
    $trigger_dml_stmts{replace} = join("\n",
        "REPLACE INTO $new_table_name_quote",
        "    ($column_list_str)",
        "VALUES",
        "    ($new_column_list_str)",
    );

    my $update_unique_where_str = join(' AND ',
        (map {
            join(
                # Use NULL-safe equals, since unique indexes could be nullable
                " $nseo ",
                "OLD.".$dbh->quote_identifier($_),
                "NEW.".$dbh->quote_identifier($_),
            );
        } @unique_ids)
    );

    my $delete_unique_where_str = join(' AND ',
        (map {
            join(
                # Use NULL-safe equals, since unique indexes could be nullable
                " $nseo ",
                "$new_table_name_quote.".$dbh->quote_identifier($_),
                "OLD.".$dbh->quote_identifier($_),
            );
        } @unique_ids)
    );

    # For the UPDATE trigger, DELETE the row, but only if the unique IDs have been
    # changed.  The "NOT ($update_unique_where_str)" part keeps from deleting rows where
    # the unique ID is untouched.
    $trigger_dml_stmts{delete_for_update} = join("\n",
        "DELETE FROM $new_table_name_quote WHERE",
        "    NOT ($update_unique_where_str) AND",
        "    $delete_unique_where_str"
    );

    $trigger_dml_stmts{delete_for_delete} = join("\n",
        "DELETE FROM $new_table_name_quote WHERE",
        "    $delete_unique_where_str"
    );

    $helper->modify_trigger_dml_stmts( \%trigger_dml_stmts );

    foreach my $trigger_type (qw< INSERT UPDATE DELETE >) {
        my $trigger_header = join(' ',
            "CREATE TRIGGER ".$vars->{trigger_names_quoted}{$trigger_type},
            "AFTER $trigger_type ON $orig_table_name_quote FOR EACH ROW"
        );

        # Even though some of these are just a single SQL statement, not every RDBMS
        # (like SQLite) supports leaving out the BEGIN/END keywords.
        my $trigger_sql = join("\n",
            $trigger_header,
            "BEGIN",
            '',
        );

        if    ($trigger_type eq 'INSERT') {
            # INSERT trigger: Just a REPLACE command
            $trigger_sql .= $trigger_dml_stmts{replace}.';';
        }
        elsif ($trigger_type eq 'UPDATE') {
            # UPDATE trigger: DELETE special unique ID changes, then another REPLACE command.
            $trigger_sql .= join("\n",
                $trigger_dml_stmts{delete_for_update}.';',
                $trigger_dml_stmts{replace}.';',
            );
        }
        elsif ($trigger_type eq 'DELETE') {
            # DELETE trigger: Just a DELETE command
            $trigger_sql .= $trigger_dml_stmts{delete_for_delete}.';';
        }
        $trigger_sql .= "\nEND";

        # DOIT!
        $self->dbh_runner_do($trigger_sql);

        $reversible->add_undo(sub {
            $self->dbh_runner_do( "DROP TRIGGER IF EXISTS ".$self->_vars->{trigger_names_quoted}{$trigger_type} );
        });
    }

    $progress->update;
}

#pod =head2 copy_rows
#pod
#pod Fires up a L process to copy all of the rows from the old table to
#pod the new.
#pod
#pod =cut

sub copy_rows {
    my $self = shift;
    my $dbh  = $self->dbh;
    my $vars = $self->_vars;

    my $progress  = $vars->{progress_bar};
    my $copy_opts = $self->_fill_copy_opts;

    $progress->message("Copying all rows to the new table");

    DBIx::BatchChunker->construct_and_execute( %$copy_opts );
    $vars->{new_table_copied} = 1;

    # Analyze the table, since we have a ton of new rows now
    $progress->message("Analyzing table");
    $self->_helper->analyze_table( $self->new_table_name );

    $progress->update;
}

#pod =head2 swap_tables
#pod
#pod With the new table completely modified and set up, this swaps the old/new tables.
#pod
#pod =cut

sub swap_tables {
    my $self = shift;
    my $dbh  = $self->dbh;
    my $vars = $self->_vars;

    my $progress   = $vars->{progress_bar};
    my $reversible = $self->reversible;
    my $helper     = $self->_helper;

    my $catalog         = $vars->{catalog};
    my $schema          = $vars->{schema};
    my $orig_table_name = $self->table_name;
    my $new_table_name  = $self->new_table_name;

    my $escape = $dbh->get_info( $GetInfoType{SQL_SEARCH_PATTERN_ESCAPE} ) // '\\';

    # Fire the before_swap hook
    $self->fire_hook('before_swap');

    if ($helper->dbms_uses_global_fk_namespace || $helper->child_fks_need_adjusting) {
        # The existing parent/child FK list needs to be captured prior to the swap.  The FKs
        # have already been created, and possibly changed/deleted, from the new table, so we
        # use that as reference.  They have *not* been re-created on the child tables, so
        # the original table is used as reference.
        my $fk_hash = $vars->{foreign_keys}{definitions} //= {};
        $self->dbh_runner(run => set_subname '_fk_info_query', sub {
            $dbh = $_;
            $fk_hash->{parent} = $self->_fk_info_to_hash( $helper->foreign_key_info(undef, undef, undef, $catalog, $schema, $new_table_name)  );
            $fk_hash->{child}  = $self->_fk_info_to_hash( $helper->foreign_key_info($catalog, $schema, $orig_table_name, undef, undef, undef) );
        });
    }

    # Find an "_old" table name first
    my $old_table_name = $vars->{old_table_name} = $self->_find_new_identifier(
        "_${orig_table_name}_old" => set_subname('_old_table_name_finder', sub {
            my ($d, $like_expr) = @_;
            $like_expr =~ s/([_%])/$escape$1/g;

            $d->table_info($catalog, $schema, $like_expr)->fetchrow_array;
        }),
        'SQL_MAXIMUM_TABLE_NAME_LENGTH',
    );
    my $old_table_name_quote = $dbh->quote_identifier($old_table_name);

    $progress->message("Swapping tables ($new_table_name --> $orig_table_name --> $old_table_name)");

    # Let's swap tables!
    $helper->swap_tables($new_table_name, $orig_table_name, $old_table_name);

    # Kill the undo stack now, just in case something weird happens between now and the
    # end of the reversibly block.  We've reached a "mostly successful" state, so rolling
    # back here would be undesirable.
    $reversible->clear_undo;
    $vars->{new_table_swapped} = 1;

    $progress->update;
}

#pod =head2 drop_old_table
#pod
#pod Drops the old table.  This will also remove old foreign keys on child tables.  (Those FKs
#pod are re-applied to the new table in the next step.)
#pod
#pod =cut

sub drop_old_table {
    my $self = shift;
    my $dbh  = $self->dbh;
    my $vars = $self->_vars;

    my $progress   = $vars->{progress_bar};
    my $reversible = $self->reversible;
    my $helper     = $self->_helper;

    my $old_table_name       = $vars->{old_table_name};
    my $old_table_name_quote = $dbh->quote_identifier($old_table_name);

    $reversible->failure_warning( join "\n",
        '',
        "The new table has been swapped, but since the process was interrupted, foreign keys will",
        "need to be cleaned up, and the old table dropped.",
        '',
    );

    # The RDBMS may complain about dangling non-functional FKs if the DROP happens first,
    # so let's remove those child FKs first, and reapply them later.  We turn off FK
    # checks, so these constraint drops are quick and low risk.
    #
    # SQLite doesn't actually support DROP CONSTRAINT, but it doesn't do any messy business with
    # FK renames, either.  So, SQLite can just skip this step.
    if ($helper->child_fks_need_adjusting) {
        $progress->message("Removing FKs from child tables");

        $self->dbh_runner_do(
            $helper->remove_fks_from_child_tables_stmts
        );
    }

    # Now, the actual DROP
    $progress->message("Dropping old table $old_table_name");

    $self->dbh_runner_do("DROP TABLE $old_table_name_quote");

    $progress->update;
}

#pod =head2 cleanup_foreign_keys
#pod
#pod Clean up foreign keys on both the new and child tables.
#pod
#pod =cut

sub cleanup_foreign_keys {
    my $self = shift;
    my $dbh  = $self->dbh;
    my $vars = $self->_vars;

    my $progress   = $vars->{progress_bar};
    my $reversible = $self->reversible;
    my $helper     = $self->_helper;

    $reversible->failure_warning( join "\n",
        '',
        "The new table is live, but since the process was interrupted, foreign keys will need to be",
        "cleaned up.",
        '',
    );

    if ($helper->dbms_uses_global_fk_namespace) {
        # The DB has global namespaces for foreign keys, so we are renaming them back to
        # their original names.  The original table has already been dropped, so there's
        # no more risk of bumping into that namespace.
        $progress->message("Renaming parent FKs back to the original constraint names");

        $self->dbh_runner_do(
            $helper->rename_fks_back_to_original_stmts
        );
    }

    if ($helper->child_fks_need_adjusting) {
        # Since we captured the child FK names prior to the swap, they should have the
        # original FK names, even before MySQL's "helpful" changes on "${tbl_name}_ibfk_" FK
        # names.
        $progress->message("Adding FKs back on child tables");

        $self->dbh_runner_do(
            $helper->add_fks_back_to_child_tables_stmts
        );
    }

    $progress->update;
}

### Private methods

sub _find_new_identifier {
    my ($self, $desired_identifier, $finder_sub, $length_info_str) = @_;
    $length_info_str ||= 'SQL_MAXIMUM_IDENTIFIER_LENGTH';

    state $hash_digits = ['a' .. 'z', '0' .. '9'];

    my $hash = join '', map { $hash_digits->[rand @$hash_digits] } 1 .. 10;

    # Test out some potential names
    my @potential_names = (
        $desired_identifier, "_${desired_identifier}",
        "${desired_identifier}_${hash}", "_${desired_identifier}_${hash}",
        $hash, "_${hash}"
    );

    my $max_len = $self->dbh->get_info( $GetInfoType{$length_info_str} ) || 256;

    my $new_name;
    foreach my $potential_name (@potential_names) {
        $potential_name = substr($potential_name, 0, $max_len);  # avoid the ID name character limit

        my @results = $self->dbh_runner(run => set_subname '_find_new_identifier_dbh_runner', sub {
            $finder_sub->($_, $potential_name);
        });

        # Skip if we found it
        next if @results;

        $new_name = $potential_name;
        last;
    }

    # This really shouldn't happen...
    die "Cannot find a proper identifier name for $desired_identifier!  All of them are taken!" unless defined $new_name;

    return $new_name;
}

sub _column_list {
    my $self = shift;
    my $dbh  = $self->dbh;
    my $vars = $self->_vars;

    my $catalog         = $vars->{catalog};
    my $schema          = $vars->{schema};
    my $orig_table_name = $self->table_name;
    my $new_table_name  = $self->new_table_name;

    my (@old_column_list, @new_column_list);
    $self->dbh_runner(run => set_subname '_column_list_runner', sub {
        $dbh = $_;
        @old_column_list =
            map { $_->{COLUMN_NAME} }
            @{ $dbh->column_info( $catalog, $schema, $orig_table_name, '%' )->fetchall_arrayref({ COLUMN_NAME => 1 }) }
        ;
        @new_column_list =
            map { $_->{COLUMN_NAME} }
            @{ $dbh->column_info( $catalog, $schema, $new_table_name, '%' )->fetchall_arrayref({ COLUMN_NAME => 1 }) }
        ;
    });

    # We only care about columns that exist in both tables.  If a column was added on the
    # new table, there's no data to copy.  If a column was deleted from the new table, we
    # don't care about keeping it.
    my %new_column_set = map { $_ => 1 } @new_column_list;
    return grep { $new_column_set{$_} } @old_column_list;
}

sub _fk_info_to_hash {
    my ($self, $fk_sth) = @_;
    my $vars = $self->_vars;
    my $dbh  = $self->dbh;

    # NOTE: Need to account for alternate ODBC names

    my @fk_rows = @{ $fk_sth->fetchall_arrayref({}) };
    @fk_rows = sort {
        # Sort by FK name, then by the column sequence number
        $a->{FK_NAME} cmp $b->{FK_NAME} ||
        ($a->{KEY_SEQ} // $a->{ORDINAL_POSITION}) <=> ($a->{KEY_SEQ} // $a->{ORDINAL_POSITION})
    } @fk_rows;

    my (%fks, %create_table_sql);
    foreach my $row (@fk_rows) {
        # Some of these rows aren't even FKs
        next unless $row->{PKTABLE_NAME} || $row->{UK_TABLE_CAT};
        next unless $row->{FKTABLE_NAME} || $row->{FK_TABLE_NAME};

        my $fk_name       = $row->{FK_NAME}      // $row->{FKCOLUMN_NAME};
        my $fk_table_name = $row->{FKTABLE_NAME} // $row->{FK_TABLE_NAME};

        my $key = join( '.',
            $row->{PKTABLE_NAME} // $row->{UK_TABLE_CAT},
            $fk_name,
        );

        # Since there may be multiple columns per FK, those associated columns are
        # arrayrefs.
        unless ($fks{$key}) {

            $fks{$key} = {
                fk_name       => $fk_name,

                # The table where the original PK exists
                pk_table_name => $row->{PKTABLE_NAME} // $row->{UK_TABLE_CAT},
                pk_columns    => [ $row->{PKCOLUMN_NAME} // $row->{UK_COLUMN_NAME} ],

                # The table where the FK constraint has been declared
                fk_table_name => $fk_table_name,
                fk_columns    => [ $row->{FKCOLUMN_NAME} // $row->{FK_COLUMN_NAME} ],
            };

            # Sadly, foreign_key_info doesn't always fill in all of the details for the FK, so the
            # CREATE TABLE SQL is actually the better record.  Fortunately, this is all ANSI SQL.
            my $create_table_sql = $create_table_sql{$fk_table_name} //= $self->_helper->create_table_sql($fk_table_name);
            my $fk_name_quote_re = '(?:'.join('|',
                quotemeta( $dbh->quote_identifier($fk_name) ), quotemeta('"'.$fk_name.'"'), quotemeta($fk_name)
            ).')';

            if ($create_table_sql =~ m<
                CONSTRAINT \s $fk_name_quote_re \s (      # start capture of full SQL
                    FOREIGN \s KEY \s \( [^\)]+ \) \s     # "FOREIGN KEY" plus column list (which we already have above)
                    REFERENCES \s [^\(]+ \s \( [^\)]+ \)  # "REFERENCES" plus table+column list (again, already captured above)
                    \s? ( [^\)\,]* )                      # ON DELETE/UPDATE, DEFER, MATCH, etc.
                )                                         # end capture of full SQL
            >isx) {
                my ($fk_sql, $extra_sql) = ($1, $2);
                $fk_sql =~ s/^\s+|\s+$//g;

                $fks{$key}{fk_sql}      = $fk_sql;
                $fks{$key}{delete_rule} = $1 if $extra_sql =~ /ON DELETE ((?:SET |NO )?\w+)/i;
                $fks{$key}{update_rule} = $1 if $extra_sql =~ /ON UPDATE ((?:SET |NO )?\w+)/i;
                $fks{$key}{defer}       = $1 if $extra_sql =~ /((?:NOT )?DEFERRABLE(?: INITIALLY \w+)?)/i;
                $fks{$key}{match}       = $1 if $extra_sql =~ /(MATCH \w+)/i;
            }
        }
        else {
            push @{ $fks{$key}{pk_columns} }, $row->{PKCOLUMN_NAME} // $row->{UK_COLUMN_NAME};
            push @{ $fks{$key}{fk_columns} }, $row->{FKCOLUMN_NAME} // $row->{FK_COLUMN_NAME};
        }
    }

    return \%fks;
}

sub _fk_to_sql {
    my ($self, $fk) = @_;
    my $dbh = $self->dbh;

    # Everything after the CONSTRAINT keyword (ANSI SQL)

    if ($fk->{fk_sql}) {
        # Already have most of the SQL
        return join(' ',
            $dbh->quote_identifier($fk->{fk_name}),
            $fk->{fk_sql},
        );
    }

    return join(' ',
        $dbh->quote_identifier($fk->{fk_name}),
        'FOREIGN KEY',
        '('.join(', ', map { $dbh->quote_identifier($_) } @{ $fk->{fk_columns} }).')',
        'REFERENCES',
        $dbh->quote_identifier($fk->{pk_table_name}),
        '('.join(', ', map { $dbh->quote_identifier($_) } @{ $fk->{pk_columns} }).')',
        ( $fk->{match}       ? $fk->{match}                    : () ),
        ( $fk->{delete_rule} ? 'ON DELETE '.$fk->{delete_rule} : () ),
        ( $fk->{update_rule} ? 'ON UPDATE '.$fk->{update_rule} : () ),
        ( $fk->{defer}       ? $fk->{defer}                    : () ),
    );
}

#pod =head1 SEE ALSO
#pod
#pod =over
#pod
#pod =item *
#pod
#pod L
#pod
#pod =item *
#pod
#pod L
#pod
#pod =item *
#pod
#pod L
#pod
#pod =item *
#pod
#pod L
#pod
#pod =back
#pod
#pod =head1 WHY YET ANOTHER OSC?
#pod
#pod The biggest reason is that none of the above fully support foreign key constraints.
#pod Percona's C comes close, but also includes this paragraph:
#pod
#pod     Due to a limitation in MySQL, foreign keys will not have the same names after the ALTER
#pod     that they did prior to it. The tool has to rename the foreign key when it redefines it,
#pod     which adds a leading underscore to the name. In some cases, MySQL also automatically
#pod     renames indexes required for the foreign key.
#pod
#pod So, tables swapped with C are not exactly what they used to be before the swap.
#pod It also had a number of other quirks that just didn't work out for us, related to FKs and
#pod the amount of switches required to make it (semi-)work.
#pod
#pod Additionally, by making DBIx::OnlineDDL its own Perl module, it's a lot easier to run
#pod Perl-based schema changes along side L without having to switch
#pod between Perl and CLI.  If other people want to subclass this module for their own
#pod environment-specific quirks, they have the power to do so, too.
#pod
#pod =cut

1;

__END__