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[Cache] add integration with Messenger to allow computing cached values in a worker #30572

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Merged
merged 1 commit into from
Sep 12, 2020
Merged

[Cache] add integration with Messenger to allow computing cached values in a worker #30572

merged 1 commit into from
Sep 12, 2020

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nicolas-grekas
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@nicolas-grekas nicolas-grekas commented Mar 14, 2019 •
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Q A
Branch? master
Bug fix? no
New feature? yes
BC breaks? no
Deprecations? no
Tests pass? yes
Fixed tickets -
License MIT
Doc PR -

This PR needs and for now embeds #30334. See 2nd commit.

Using the new CacheInterface enables probabilistic early expiration by default. This means that from time to time, items are elected as early-expired while they are still fresh (see Wikipedia for details).

This PR adds a new early_expiration_message_bus option when configuring cache pools. When this option is set, cache pools are configured to send those early-expired items on a Messenger bus, then serve the current value immediately, while the updated value is computed in a worker in the background.

CacheInterface::get($key, $callback) accepts any callable, but sending any callable on a bus is not possible (e.g. a Closure cannot be serialized). To bypass this constraint, this feature works only with callables in the form [$service, 'publicMethod'], where $service is any public or reversible service.

This constraint is a serious one: this $service must compute a value when knowing only its key. This means keys should embed enough information for this to happen. I think that's not that hard - and we may find ways to provide additional context in the future.

At least the goal is worth it: in theory, this strategy allows achieving a 100% hit ratio even when invalidation-by-expiration is used.

There are two things one needs to do to enable this behavior:

  1. bind a message bus to a cache pool:
framework:
    cache:
        pools:
            test.cache:
                early_expiration_message_bus: messenger.default_bus
  1. route EarlyExpirationMessage to a transport:
framework:
    messenger:
        routing:
            'Symfony\Component\Cache\Messenger\EarlyExpirationMessage': amqp

@nicolas-grekas nicolas-grekas added this to the next milestone Mar 14, 2019
Nyholm
Nyholm reviewed Mar 15, 2019
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Cool. I really like this feature.

Could you show a code example how I would use it.

I’m also trying to figure out how I can work around the limitation..

@nicolas-grekas
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@Nyholm thanks for having a look :)

To test this, you need to configure a pool with the messenger_bus option set, and have the consumer run:

framework:
    cache:
        pools:
            test.cache:
                messenger_bus: message_bus
    messenger:
        transports:
            amqp: '%env(MESSENGER_TRANSPORT_DSN)%'
        routing:
            'Symfony\Component\Cache\Messenger\Message': amqp

BTW, this shows another area where Messenger needs to improve: how should a bundle provide configuration for this Message-to-transport mapping out of the box? ping @sroze @ogizanagi @weaverryan.

Then e.g. in a controller:

    /**
     * @Route("/test", name="test")
     */
    public function index(CacheInterface $testCache)
    {
        $value = $testCache->get('foo', [$this, 'compute']);

        return $this->render('test/index.html.twig', [
            'value' => $value,
        ]);
    }

    public function compute(ItemInterface $item)
    {
        $item->expiresAfter(5);
        sleep(1);

        return sprintf('#%06X', mt_rand(0, 0xFFFFFF));
    }

Runnig the dev weberver: symfony serve
Running the worker: bin/console messenger:consume -vvv
etc.

@nicolas-grekas nicolas-grekas force-pushed the cache-bus branch 4 times, most recently from 4020350 to 4f69bb1 Compare March 15, 2019 13:41
@nicolas-grekas
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See https://github.com/nicolas-grekas/cache-bus for a running example.

@sroze
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sroze commented Mar 19, 2019

Looks like a great idea 😍

@tgalopin
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tgalopin commented Apr 6, 2019

What's the status of this PR? I feel everyone concerned is at the EU hackathon, could be a great opportunity to merge :)

sroze
sroze reviewed Apr 6, 2019
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It's black magic

@nicolas-grekas nicolas-grekas changed the base branch from master to 4.4 June 2, 2019 20:04
@nicolas-grekas nicolas-grekas modified the milestones: next, 4.4 Oct 27, 2019
@nicolas-grekas nicolas-grekas modified the milestones: 4.4, next Nov 4, 2019
@fabpot
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fabpot commented Apr 5, 2020

Can you rebase and perhaps answers the few questions?

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Plopix commented May 8, 2020

I would love to see this merged/updated to be merged! I think that is a great addition for performances

@nicolas-grekas nicolas-grekas changed the base branch from 4.4 to master September 7, 2020 13:36
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I'm adding tests, that should be ok in a few hours.

@nicolas-grekas nicolas-grekas force-pushed the cache-bus branch 3 times, most recently from d067d1b to 5880f9b Compare September 8, 2020 17:51
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I rebased the PR and added unit tests. It works \o/

I also verified on the demo app I built last year, all works as expected 🎉

Status: needs review

@bastnic
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bastnic commented Sep 9, 2020

Stunning idea!

@fabpot
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fabpot commented Sep 11, 2020

@nicolas-grekas Can you fix the tests?

@nicolas-grekas nicolas-grekas force-pushed the cache-bus branch 2 times, most recently from c2f5b44 to 0de9af9 Compare September 11, 2020 13:32
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fabpot commented Sep 12, 2020

Thank you @nicolas-grekas.

@fabpot fabpot mentioned this pull request Sep 12, 2020
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@fabpot fabpot merged commit adedd76 into symfony:master Sep 12, 2020
@nicolas-grekas nicolas-grekas deleted the cache-bus branch September 14, 2020 09:19
@nicolas-grekas nicolas-grekas modified the milestones: next, 5.2 Oct 5, 2020
@fabpot fabpot mentioned this pull request Oct 5, 2020
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@dunglas dunglas Awaiting requested review from dunglas

@jderusse jderusse Awaiting requested review from jderusse

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@nicolas-grekas @sroze @tgalopin @fabpot @Plopix @bastnic @Tobion @Nyholm @michaelcullum @carsonbot