This really does come down to the fundamental tradeoff previously
discussed in various places regarding transactions and autocommit;
That is, that the connection is not necessarily monopolized by
dbix-class. When it comes 'online' with the connection from whatever
pool it came from, there may or may not have been any statements
executed since the last commit/rollback! You may also have executed
modification commands within dbix-class outside a txn_do command - do
you want those to dissappear or become part of the transaction?
Thus to my understanding, when you turn off autocommit, dbix-class goes
into a 'safety' mode, stating something like:
"I cannot know how to reconstruct the entire transaction because
previous statements may have been executed before the connection or
before the txn_do. I do not know if its okay to roll them back or if
its okay to commit them, and I certainly can't redo them (since I don't
know of them) if I lose connection - so I won't do anything at all"
I was rather miffed to discover this myself, and half-created a patch to
fix that behavior when I learned that it was intentional!
So I created an alternative I call 'trust_dbic_transactions'. When this
is enabled, I am enforcing the simple application/system rule of:
If you execute any statements on the database without explicitly
commiting it, preferably through a txn_do transaction, it will be rolled
back.
With that rule in place, it no longer becomes necessary to hedge one's
bets against what was done outside the txn_do. Use txn_do to make
modifications to the db or they don't happen.
The maintainers of DBIx::Class don't seem to find my code quality use
case (in a nutshell enforceing the rule break-early-break-often, hence
making bugs easier to find) impressive or useful and though they have
expressed mild interest in what I've done, I have heard no follow-up
interest in adding the feature to the standard module.
David
PS: In some databases doing multiple begins starts a multi-layer
transaction. Though Mysql does not do this, I think sybase may and I'm
pretty sure MSSQL, Oracle and DB2 do. This multi-layer transactional
behavior may be masked by dbic's implementation which only executes one
begin and holds off on further until the final commit.
Robert Heinzmann wrote:
Hello,
I'm using DBIx::Class and I want to implement manual transactions.
Connection is set to "AutoCommit => 0". I issue manual
----
txn_begin()
Insert
Update
Select
txn_commit() / txn_rollback()
----
However no Transaction takes place. DBIC Trace shows no BEGIN or COMMIT
/ ROLLBACK.
I added the following:
print Dumper($db->storage->{transaction_depth});
$db->storage()->txn_begin() or $logger->error_die("ERROR Starting
Transaction");
print Dumper($db->storage->{transaction_depth});
print Dumper($db->storage->{transaction_depth});
$db->storage()->txn_rollback() or $logger->error_die("ERROR Starting
Transaction");
print Dumper($db->storage->{transaction_depth});
This gives
$VAR1 = 1;
$VAR1 = 2;
$VAR1 = 2;
$VAR1 = 1;
----
/usr/share/perl5/DBIx/Class/Storage/DBI.pm
(Version Lenny: ii libdbix-class-perl 0.08010-2
Extensible and flexible object <-> relational mapper)
----
sub txn_begin {
my $self = shift;
$self->ensure_connected();
if($self->{transaction_depth} == 0) {
$self->debugobj->txn_begin()
if $self->debug;
# this isn't ->_dbh-> because
# we should reconnect on begin_work
# for AutoCommit users
$self->dbh->begin_work;
}
$self->{transaction_depth}++;
}
sub txn_commit {
my $self = shift;
if ($self->{transaction_depth} == 1) {
my $dbh = $self->_dbh;
$self->debugobj->txn_commit()
if ($self->debug);
$dbh->commit;
$self->{transaction_depth} = 0
if $self->_dbh_autocommit;
}
elsif($self->{transaction_depth} > 1) {
$self->{transaction_depth}--
}
}
sub ensure_connected {
my ($self) = @_;
unless ($self->connected) {
$self->_populate_dbh;
}
}
sub _populate_dbh {
my ($self) = @_;
my @info = @{$self->_dbi_connect_info || []};
$self->_dbh($self->_connect(@info));
# Always set the transaction depth on connect, since
# there is no transaction in progress by definition
$self->{transaction_depth} = $self->_dbh_autocommit ? 0 : 1;
if(ref $self eq 'DBIx::Class::Storage::DBI') {
my $driver = $self->_dbh->{Driver}->{Name};
if
($self->load_optional_class("DBIx::Class::Storage::DBI::${driver}")) {
bless $self, "DBIx::Class::Storage::DBI::${driver}";
$self->_rebless() if $self->can('_rebless');
}
}
my $connection_do = $self->on_connect_do;
$self->_do_connection_actions($connection_do) if ref($connection_do);
$self->_conn_pid($$);
$self->_conn_tid(threads->tid) if $INC{'threads.pm'};
}
For me this means with AutoCommit => 0 I cant do any transactions at all
...
Looks like a bug ?
P.s. Storage is Sybase. Any hints ?
Regards,
Robert
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_______________________________________________
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Searchable Archive: http://www.grokbase.com/group/[email protected]
