NAME
DBIx::TxnPool - Massive SQL updates by means of transactions with the
deadlock & signal solution for MySQL and MariaDB.
SYNOPSIS
This module will help to you to make quickly DML statements of InnoDB
engine. You can forget about deadlocks ;-)
use DBIx::TxnPool;
my $pool = txn_item {
my ( $pool, $item ) = @_;
$pool->dbh->do( "UPDATE table SET val=? WHERE key=?", undef, $_->{val}, $_->{key} );
# or
$dbh->do("INSERT INTO table SET val=?, key=?", undef, $_->{val}, $_->{key} );
}
txn_post_item {
my ( $pool, $item ) = @_;
# Here we are if transaction is successful
unlink( 'some_file_' . $_->{key} );
# or
unlink( 'some_file_' . $item->{key} );
}
txn_commit {
my $pool = shift;
log( 'The commit was here...' );
} dbh => $dbh, size => 100;
# Here can be deadlocks but they will be resolved by module
# and repeated (to see example in xt/03_deadlock_solution.t)
$pool->add( { key => int( rand(100) ), val => $_ } ) for ( 0 .. 300 );
$pool->finish;
Or other way:
my $pool = txn_item {
$dbh->do( "UPDATE table SET val=? WHERE key=?", undef, $_->{val}, $_->{key} );
}
txn_sort {
$a->{key} <=> $b->{key}
}
dbh => $dbh, size => 100;
# Here no deadlocks because all keys are sorted before transaction:
# circle blocks inside the InnoDB not occur
$pool->add( { key => int( rand(100) ), val => $_ } ) for ( 0 .. 300 );
$pool->finish;
DESCRIPTION
If you need massive quickly updates or inserts into InnoDB database -
this module for you! It helps to wrap some SQL manipulation statements
to one transaction and has the deadlock and signal solution.
DETAILS
If you make alone insert/delete/update statement in the InnoDB engine,
MySQL server does fsync (data flushing to disk) after each statement. It
can be very slow for many updates. The best solution can be to wrap some
insert/delete/update statements in one transaction for example. But this
raises a new problem - deadlocks. If a deadlock occurs a DBI module
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 your pool to be fed by
your data, it wraps data in one transaction up to the maximum defined
size or up to the finish method. If deadlock occurs a pool 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
Please to see "SYNOPSIS" section
Shortcuts:
The "txn_item" should be first. Other sortcuts can follow in any order.
Parameters should be the last.
txn_item (Required)
The transaction item callback. There 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. Please don't catch exceptions here (by
try{} or eval{} for example) - by this way deadlocks are defined
outside under the hood!
txn_sort (Optional)
Here you can define sort function for your data before a transaction
will be made. If you have only one type SQL statement in txn_item
but you didn't sort keys before transaction you can have deadlocks
(they will be resolved and transaction will be repeated but you will
lose a processing time) unless you define this function. This method
minimize deadlock events!
txn_post_item (Optional)
The post transaction item callback. This code will be executed once
for each item (defined in $_). It is located outside of the
transaction. And it will be called if whole transaction was
successful. Passing arguments are *DBIx::TxnPool* object and
*current item* respectively. You can do here your own error handling
in callback. If your code here will throw an excetption it will be
propagated above.
txn_commit (Optional)
This callback will be called after each SQL commit statement. Here
you can put code for logging for example. The first argument is
*DBIx::TxnPool* object
Parameters:
dbh (Required)
The dbh to be needed for begin_work & commit method (wrap in a
transaction).
size (Optional)
The size of pool when a commit method will be called when feeding
reaches the same size.
block_signals (Optional)
An arrayref of signals (strings) which should be blocked in slippery
places for this *pool*. Defaults are [ qw( TERM INT ) ]. You can
change globaly this list by setting: "$DBIx::TxnPool::BlockSignals =
[ qw( TERM INT ALARM ... ) ]". For details to see here "SIGNAL
HANDLING"
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)
SIGNAL HANDLING
In DBD::mysql and may be in other DB drivers there is a some bad
behavior the bug as i think. If a some signal will arrive (TERM, INT and
other) in your program during a some SQL socket work this driver throws
an exception like "MySQL lost connection". It happens because the "recv"
or "read" system calls into MySQL driver return with error code "EINTR"
if signal arrives inside this system call. A right written software
should recall a system call again because the "EINTR" is not fatal
error. But i think MySQL driver decides this error as *lost connection
error*. *"Deferred Signals"* (or Safe Signals) of perl don't help
because the MySQL driver uses direct system calls.
Workaround is to use Signal::Mask module for example and to block these
signals (TERM / INT) during working with DBI subroutines. The version
0.09 of "DBIx::TxnPool" has helpers for this. The "DBIx::TxnPool" wraps
all slippery places by blocking your preferred signals (defaults are
"TERM" & "INT" ones) before entering and by unblocking after (for
example the callback handler txn_item and transaction code). This should
minimize raised errors like the "MySQL lost connection".
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