/ 
Dancer2-Plugin-DBIC-Async-0.03
/ Dancer2::Plugin::DBIC::Async

NAME

Dancer2::Plugin::DBIC::Async - Asynchronous DBIx::Class::Async plugin for Dancer2

VERSION

Version 0.03

BENEFITS

The primary benefit of Dancer2::Plugin::DBIC::Async over the standard Dancer2::Plugin::DBIC is the ability to handle high-concurrency database operations without blocking the web server's worker processes.

In a standard sync environment, every database query is a "stop-the-world" event for that specific request handler. In an async environment, the worker can handle other tasks while waiting for the database to respond.

Non-Blocking I/O (Concurrency)

In a traditional sync app, if a database query takes 500ms, that Dancer2 worker is "busy" and cannot accept any other incoming requests for that half a second.

Sync

10 workers can handle exactly 10 simultaneous long-running queries. The 11th user must wait in the TCP queue.

Async

A single worker can initiate dozens of database queries. While the database is processing the data, the worker remains free to handle other incoming requests or perform other I/O tasks.

Parallelism within a Single Route

With the sync plugin, if you need to fetch data from five different tables that don't depend on each other, you must do them sequentially. With the async plugin, you can fire all five queries simultaneously.

# Regular Sync (Total time = sum of all queries)
my $user    = rset('User')->find(1);
my $posts   = rset('Post')->search({ uid => 1 });
my $friends = rset('Friend')->search({ uid => 1 });

# Async (Total time = the time of the single slowest query)
my $user_f    = async_rs('User')->find(1);
my $posts_f   = async_rs('Post')->search({ uid => 1 });
my $friends_f = async_rs('Friend')->search({ uid => 1 });

# Wait for all to finish
my ($user, $posts, $friends) = Future->wait_all($user_f, $posts_f, $friends_f)->get;

Integration with Modern Event Loops

The async plugin allows your Dancer2 app to play nicely with IO::Async, Mojo::IOLoop, or AnyEvent. This is critical if your app also needs to:

- Talk to external WebSockets.
- Call multiple Microservices via async HTTP clients.
- Perform background processing without a separate task runner like Minion.

Better Resource Utilisation

Sync apps often solve scaling issues by adding more worker processes (e.g., increasing Starman workers). However, each worker consumes significant RAM.

Sync Scaling

High Memory usage (100 workers = 100x memory).

Async Scaling

Low Memory usage (1 worker handles 100 connections).

DEMO

To illustrate the power of async in Dancer2, let's take a common scenario: a "User Dashboard".

In a standard sync route, the server waits for the database three separate times. If each query takes 100ms, the user waits 300ms plus overhead.

With the async plugin, the total wait time is just 100ms (the time of the slowest query) because they run in parallel.

The Synchronous Way

This blocks the worker process three times in a row.

get '/dashboard/:id' => sub {
    my $id = route_parameters->get('id');

    # Each line below stops the entire process until the DB responds
    my $user     = rset('User')->find($id);
    my @posts    = rset('Post')->search({ author_id => $id })->all;
    my @comments = rset('Comment')->search({ user_id => $id })->all;

    return template 'dashboard', {
        user     => $user,
        posts    => \@posts,
        comments => \@comments,
    };
};
The Asynchronous Way

This fires all queries at once. The worker process can even handle other people's requests while the database is working on these three queries.

get '/dashboard/:id' => sub {
    my $id = route_parameters->get('id');

    # Fire all queries simultaneously
    # These return "Future" objects immediately
    my $user_f     = async_rs('User')->find($id);
    my $posts_f    = async_rs('Post')->search({ author_id => $id })->all;
    my $comments_f = async_rs('Comment')->search({ user_id => $id })->all;

    # Combine the futures into one master future
    my $combined_f = Future->wait_all($user_f, $posts_f, $comments_f);

    # Wait for the database results (non-blocking if using an async server like Twiggy)
    $combined_f->get;

    return template 'dashboard', {
        user     => $user_f->get,
        posts    => [ $posts_f->get ],
        comments => [ $comments_f->get ],
    };
};
Advanced: Using "Then" (Chaining)

Sometimes you need the result of one query to start the next. You can chain them so the worker stays free between the steps.

get '/profile/:username' => sub {
    my $name = route_parameters->get('username');

    return async_rs('User')->find({ username => $name })->then(sub {
        my $user = shift;
        die "Not found" unless $user;

        # Fetch posts only after we confirmed the user exists
        return async_rs('Post')->search({ user_id => $user->id })->all;
    })->then(sub {
        my @posts = @_;
        return "User has " . scalar(@posts) . " posts";
    })->get;
};

Key Technical Differences

Context Switching

In the sync version, the operating system might pause the process (context switch) while waiting for the disk. In the async version, the Event Loop (IO::Async) manages this, which is much lighter on the CPU.

Wait vs. Block

In the async version, we use wait_all or then. This tells the server: "Keep this request in mind, but go help other users until the data comes back."

Error Handling

Futures have built-in -on_fail> handlers, making it easier to manage database timeouts without crashing the whole worker.

SYNOPSIS

# In config.yml
plugins:
  DBIC::Async:
    default:
      schema_class: MyApp::Schema
      dsn: "dbi:SQLite:dbname=myapp.db"
      user: ""
      password: ""
      options:
        sqlite_unicode: 1
      async:
        workers: 4

# In your Dancer2 app
use Dancer2::Plugin::DBIC::Async;

get '/users' => sub {
    my $count = async_count('User')->get;
    return to_json({ count => $count });
};

get '/users/:id' => sub {
    my $user = async_find('User', route_parameters->get('id'))->get;
    return to_json($user);
};

DESCRIPTION

This plugin provides asynchronous database access using DBIx::Class::Async in Dancer2 applications.

KEYWORDS

async_db

my $async_db = async_db();
my $async_db = async_db('connection_name');

Returns the DBIx::Class::Async object for direct method calls.

async_count

my $count_future = async_count('User');
my $count_future = async_count('User', 'connection_name');
my $count = $count_future->get;

Returns a Future that resolves to the count of records.

async_find

my $user_future = async_find('User', $id);
my $user = $user_future->get;

Returns a Future that resolves to a single record.

my $users_future = async_search('User', { active => 1 });
my $users = $users_future->get;

Returns a Future that resolves to an arrayref of matching records.

async_create

my $user_future = async_create('User', { name => 'John' });
my $user = $user_future->get;

Returns a Future that resolves to the created record.

async_update

my $result_future = async_update('User', $id, { name => 'Jane' });
my $result = $result_future->get;

Returns a Future that resolves to the update result.

async_delete

my $result_future = async_delete('User', $id);
my $result = $result_future->get;

Returns a Future that resolves to the delete result.

AUTHOR

Mohammad Sajid Anwar, <mohammad.anwar at yahoo.com>

REPOSITORY

https://github.com/manwar/Dancer2-Plugin-DBIC-Async

BUGS

Please report any bugs or feature requests through the web interface at https://github.com/manwar/Dancer2-Plugin-DBIC-Async/issues. I will be notified and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

You can find documentation for this module with the perldoc command.

perldoc Dancer2::Plugin::DBIC::Async

You can also look for information at:

LICENSE AND COPYRIGHT

Copyright (C) 2026 Mohammad Sajid Anwar.

This program is free software; you can redistribute it and / or modify it under the terms of the the Artistic License (2.0). You may obtain a copy of the full license at:

http://www.perlfoundation.org/artistic_license_2_0

Any use, modification, and distribution of the Standard or Modified Versions is governed by this Artistic License.By using, modifying or distributing the Package, you accept this license. Do not use, modify, or distribute the Package, if you do not accept this license.

If your Modified Version has been derived from a Modified Version made by someone other than you,you are nevertheless required to ensure that your Modified Version complies with the requirements of this license.

This license does not grant you the right to use any trademark, service mark, tradename, or logo of the Copyright Holder.

This license includes the non-exclusive, worldwide, free-of-charge patent license to make, have made, use, offer to sell, sell, import and otherwise transfer the Package with respect to any patent claims licensable by the Copyright Holder that are necessarily infringed by the Package. If you institute patent litigation (including a cross-claim or counterclaim) against any party alleging that the Package constitutes direct or contributory patent infringement,then this Artistic License to you shall terminate on the date that such litigation is filed.

Disclaimer of Warranty: THE PACKAGE IS PROVIDED BY THE COPYRIGHT HOLDER AND CONTRIBUTORS "AS IS' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES. THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT ARE DISCLAIMED TO THE EXTENT PERMITTED BY YOUR LOCAL LAW. UNLESS REQUIRED BY LAW, NO COPYRIGHT HOLDER OR CONTRIBUTOR WILL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING IN ANY WAY OUT OF THE USE OF THE PACKAGE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.