focal (3) AnyEvent::DBI.3pm.gz
NAME
AnyEvent::DBI - asynchronous DBI access
SYNOPSIS
use AnyEvent::DBI;
my $cv = AnyEvent->condvar;
my $dbh = new AnyEvent::DBI "DBI:SQLite:dbname=test.db", "", "";
$dbh->exec ("select * from test where num=?", 10, sub {
my ($dbh, $rows, $rv) = @_;
$#_ or die "failure: $@";
print "@$_\n"
for @$rows;
$cv->broadcast;
});
# asynchronously do sth. else here
$cv->wait;
DESCRIPTION
This module is an AnyEvent user, you need to make sure that you use and run a supported event loop.
This module implements asynchronous DBI access by forking or executing separate "DBI-Server" processes
and sending them requests.
It means that you can run DBI requests in parallel to other tasks.
With DBD::mysql, the overhead for very simple statements ("select 0") is somewhere around 50% compared to
an explicit prepare_cached/execute/fetchrow_arrayref/finish combination. With DBD::SQlite3, it's more
like a factor of 8 for this trivial statement.
ERROR HANDLING
This module defines a number of functions that accept a callback argument. All callbacks used by this
module get their AnyEvent::DBI handle object passed as first argument.
If the request was successful, then there will be more arguments, otherwise there will only be the $dbh
argument and $@ contains an error message.
A convenient way to check whether an error occurred is to check $#_ - if that is true, then the function
was successful, otherwise there was an error.
METHODS
$dbh = new AnyEvent::DBI $database, $user, $pass, [key => value]...
Returns a database handle for the given database. Each database handle has an associated server
process that executes statements in order. If you want to run more than one statement in parallel,
you need to create additional database handles.
The advantage of this approach is that transactions work as state is preserved.
Example:
$dbh = new AnyEvent::DBI
"DBI:mysql:test;mysql_read_default_file=/root/.my.cnf", "", "";
Additional key-value pairs can be used to adjust behaviour:
on_error => $callback->($dbh, $filename, $line, $fatal)
When an error occurs, then this callback will be invoked. On entry, $@ is set to the error
message. $filename and $line is where the original request was submitted.
If the fatal argument is true then the database connection is shut down and your database handle
became invalid. In addition to invoking the "on_error" callback, all of your queued request
callbacks are called without only the $dbh argument.
If omitted, then "die" will be called on any errors, fatal or not.
on_connect => $callback->($dbh[, $success])
If you supply an "on_connect" callback, then this callback will be invoked after the database
connect attempt. If the connection succeeds, $success is true, otherwise it is missing and $@
contains the $DBI::errstr.
Regardless of whether "on_connect" is supplied, connect errors will result in "on_error" being
called. However, if no "on_connect" callback is supplied, then connection errors are considered
fatal. The client will "die" and the "on_error" callback will be called with $fatal true.
When on_connect is supplied, connect error are not fatal and AnyEvent::DBI will not "die". You
still cannot, however, use the $dbh object you received from "new" to make requests.
fork_template => $AnyEvent::Fork-object
"AnyEvent::DBI" uses "AnyEvent::Fork->new" to create the database slave, which in turn either
"exec"'s a new process (similar to the old "exec_server" constructor argument) or uses a process
forked early (see AnyEvent::Fork::Early).
With this argument you can provide your own fork template. This can be useful if you create a lot
of "AnyEvent::DBI" handles and want to save memory (And speed up startup) by not having to load
"AnyEvent::DBI" again and again into your child processes:
my $template = AnyEvent::Fork
->new # create new template
->require ("AnyEvent::DBI::Slave"); # preload AnyEvent::DBI::Slave module
for (...) {
$dbh = new AnyEvent::DBI ...
fork_template => $template;
timeout => seconds
If you supply a timeout parameter (fractional values are supported), then a timer is started any
time the DBI handle expects a response from the server. This includes connection setup as well as
requests made to the backend. The timeout spans the duration from the moment the first data is
written (or queued to be written) until all expected responses are returned, but is postponed for
"timeout" seconds each time more data is returned from the server. If the timer ever goes off
then a fatal error is generated. If you have an "on_error" handler installed, then it will be
called, otherwise your program will die().
When altering your databases with timeouts it is wise to use transactions. If you quit due to
timeout while performing insert, update or schema-altering commands you can end up not knowing if
the action was submitted to the database, complicating recovery.
Timeout errors are always fatal.
Any additional key-value pairs will be rolled into a hash reference and passed as the final argument
to the "DBI->connect (...)" call. For example, to suppress errors on STDERR and send them instead to
an AnyEvent::Handle you could do:
$dbh = new AnyEvent::DBI
"DBI:mysql:test;mysql_read_default_file=/root/.my.cnf", "", "",
PrintError => 0,
on_error => sub {
$log_handle->push_write ("DBI Error: $@ at $_[1]:$_[2]\n");
};
$dbh->on_error ($cb->($dbh, $filename, $line, $fatal))
Sets (or clears, with "undef") the "on_error" handler.
$dbh->timeout ($seconds)
Sets (or clears, with "undef") the database timeout. Useful to extend the timeout when you are about
to make a really long query.
$dbh->attr ($attr_name[, $attr_value], $cb->($dbh, $new_value))
An accessor for the database handle attributes, such as "AutoCommit", "RaiseError", "PrintError" and
so on. If you provide an $attr_value (which might be "undef"), then the given attribute will be set
to that value.
The callback will be passed the database handle and the attribute's value if successful.
If an error occurs and the "on_error" callback returns, then only $dbh will be passed and $@ contains
the error message.
$dbh->exec ("statement", @args, $cb->($dbh, \@rows, $rv))
Executes the given SQL statement with placeholders replaced by @args. The statement will be prepared
and cached on the server side, so using placeholders is extremely important.
The callback will be called with a weakened AnyEvent::DBI object as the first argument and the result
of "fetchall_arrayref" as (or "undef" if the statement wasn't a select statement) as the second
argument.
Third argument is the return value from the "DBI->execute" method call.
If an error occurs and the "on_error" callback returns, then only $dbh will be passed and $@ contains
the error message.
$dbh->stattr ($attr_name, $cb->($dbh, $value))
An accessor for the statement attributes of the most recently executed statement, such as "NAME" or
"TYPE".
The callback will be passed the database handle and the attribute's value if successful.
If an error occurs and the "on_error" callback returns, then only $dbh will be passed and $@ contains
the error message.
$dbh->begin_work ($cb->($dbh[, $rc]))
$dbh->commit ($cb->($dbh[, $rc]))
$dbh->rollback ($cb->($dbh[, $rc]))
The begin_work, commit, and rollback methods expose the equivalent transaction control method of the
DBI driver. On success, $rc is true.
If an error occurs and the "on_error" callback returns, then only $dbh will be passed and $@ contains
the error message.
$dbh->func ('string_which_yields_args_when_evaled', $func_name, $cb->($dbh, $rc, $dbi_err, $dbi_errstr))
This gives access to database driver private methods. Because they are not standard you cannot always
depend on the value of $rc or $dbi_err. Check the documentation for your specific driver/function
combination to see what it returns.
Note that the first argument will be eval'ed to produce the argument list to the func() method. This
must be done because the serialization protocol between the AnyEvent::DBI server process and your
program does not support the passage of closures.
Here's an example to extend the query language in SQLite so it supports an intstr() function:
$cv = AnyEvent->condvar;
$dbh->func (
q{
instr => 2, sub {
my ($string, $search) = @_;
return index $string, $search;
},
},
create_function => sub {
return $cv->send ($@)
unless $#_;
$cv->send (undef, @_[1,2,3]);
}
);
my ($err,$rc,$errcode,$errstr) = $cv->recv;
die $err if defined $err;
die "EVAL failed: $errstr"
if $errcode;
# otherwise, we can ignore $rc and $errcode for this particular func
SEE ALSO
AnyEvent, DBI, Coro::Mysql.
AUTHOR AND CONTACT
Marc Lehmann <schmorp@schmorp.de> (current maintainer) http://home.schmorp.de/ Adam Rosenstein <adam@redcondor.com> http://www.redcondor.com/