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 {
        my ( $pool, $item ) = @_;
        # $_ consists the item too

        # It's executed for every item inside one transaction maximum of size 'size'
        # this code may be recalled if deadlocks will occur

        # code has dbh & sth handle statements
        $pool->dbh->do("UPDATE ...");
        $pool->dbh->do("INSERT ...");
        $pool->dbh->do("DELETE...");
    }
    txn_post_item {
        my ( $pool, $item ) = @_;
        # $_ consists the item too
        # code executed for every item after sucessfully commited transaction
        unlink('some_file);
    }
    txn_commit {
        my $pool = shift;
        # we log here each transaction for example
        log( 'The commit was here...' );
    } 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:

The txn_item should be first. Other sortcuts can follow in any order. Parameters should be the last.

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. Passing arguments will be DBIx::TxnPool object and current item respectively.

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. Passing arguments will be DBIx::TxnPool object and current item respectively.

txn_commit (Optional)

This callback will be called after each SQL commit statement. Here you can put code for logging for example. The first argument will be DBIx::TxnPool object

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!

dbh

The accessor of dbh. It's readonly.

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

TODO

A supporting DBIx::Connector object instead DBI

To add other callbacks in future.