NAME
    DBIx::TxnPool - The helper for making SQL insert/delete/update
    statements through a transaction method with a deadlock solution

SYNOPSIS
        use DBIx::TxnPool;

        my $pool = txn_item {
            # $_ consists the one item
            # code has dbh & sth handle statements
            # It's executed for every item inside one transaction maximum of size 'size'
            # this code may be recalled if deadlocks will occur
        }
        txn_post_item {
            # $_ consists the one item
            # code executed for every item after sucessfully commited transaction
        } dbh => $dbh, size => 100;

        foreach my $i ( 0 .. 1000 ) {
            $pool->add( { i => $i, value => 'test' . $i } );
        }

        $pool->finish;

DESCRIPTION
    Sometimes i need in module which helps to me to wrap some SQL
    manipulation statements to one transaction. If you make alone
    insert/delete/update statement in the InnoDB engine, MySQL server for
    example does fsync (data flushing to disk) after each statements. It can
    be very slowly if you update 100,000 and more rows for example. The
    better way to wrap some insert/delete/update statements in one
    transaction for example. But there can be other problem - deadlocks. If
    a deadlock occur the DBI's module can throws exceptions and ideal way to
    repeat SQL statements again. This module helps to make it. It has a pool
    inside for data (FIFO buffer) and calls your callbacks for each pushed
    item. When you feed a module by your data, it wraps data in one
    transaction up to the maximum defined size or up to the finish method.
    If deadlock occurs it repeats your callbacks for every item again. You
    can define a second callback which will be executed for every item after
    wrapped transaction. For example there can be non-SQL statements, for
    example a deleting files, cleanups and etc.

CONSTRUCTOR
    The object DBIx::TxnPool created by txn_item subroutines:

        my $pool = txn_item {
            # $_ consists the one item
            # code has dbh & sth handle statements
            # It's executed for every item inside one transaction maximum of size 'size'
            # this code may be recalled if deadlocks will occur
        }
        txn_post_item {
            # $_ consists the one item
            # code executed for every item after sucessfully commited transaction
        } dbh => $dbh, size => 100;

    Or other way:

        my $pool = txn_item {
            # $_ consists the one item
            # code has dbh & sth handle statements
            # It's executed for every item inside one transaction maximum of size 'size'
            # this code may be recalled if deadlocks will occur
        } dbh => $dbh, size => 100;

  Shortcuts:
    txn_item (Required)
        The transaction's item callback. Here should be SQL statements and
        code should be safe for repeating (when a deadlock occurs). The $_
        consists a current item. You can modify it if one is hashref for
        example.

    txn_post_item (Optional)
        The post transaction item callback. This code will be executed once
        for each item (defined in $_). It is located outside of the
        transaction. And it will be called if whole transaction was
        succaessful.

  Parameters:
    dbh (Required)
        The dbh to be needed for begin_work & commit method (wrap in a
        transaction).

    size (Optional)
        The size of pool when a commit method will be called when feeding
        reaches the same size.

    max_repeated_deadlocks (Optional)
        The limit of consecutive deadlocks. The default is 5. After limit to
        be reached the "add" throws exception.

METHODS
    add You can add item of data to the pool. This method makes a wrap to
        transaction. It can finish transaction if pool reaches up to size or
        can repeat a whole transaction again if deadlock exception was
        thrown. The size of transaction may be less than your defined size!

    finish
        It makes a final transaction if pool is not empty.

    amount_deadlocks
        The amount of deadlocks (repeated transactions)

AUTHOR
    This module has been written by Perlover <perlover@perlover.com>

LICENSE
    This module is free software and is published under the same terms as
    Perl itself.

SEE ALSO
    DBI, Deadlock Detection and Rollback
    <http://dev.mysql.com/doc/refman/5.5/en/innodb-deadlock-detection.html>

TODO
    A supporting DBIx::Connector object instead DBI
    To make a DESTROY method - the alias for "finish" method.

