How Redis expires keys

redis

I am often asked by my "junior" colleagues - what happens with Redis keys after expiry time, are these expired keys automatically being deleted or are they just "hang in RAM till The End Of Times" ? *Dramatic music! :)*
Fine, if you are to lazy to read docs...

Redis keys are expired in two ways: a passive way and an active way.

Active

When client access key and the key is found to be timed out - it is being deleted.

Passive

The most interesting - what happens with keys that are expired are are never accessed after expiry.
10 times per second Redis check 100 random keys with associated expiry time from the keyspace and remove expired keys.
If more than 25 keys were expired, start check again.

This is a probabilistic algorithm, where the percentage of keys that are likely to be expired is under 25%. This means that at any given moment the maximum amount of keys already expired that are using memory is at max equal to max amount of write operations per second divided by 4. That means that about 1/4 of RAM occupied by Redis could be used to store "expired" keys.


Yii2 dev digest #3 Dec'13

Official CHANGELOG appeared so my digests could be not so useful now
but in any case I will keep going :)

Discussions

that could be interesting to participate in

Take a look into and share your view on these questions Implement Transaction strategy for database cleanup (start transaction for connection and then rollback) Implement Reset strategy for database cleanup (tables truncate) Implement Drop/Create strategy for database cleanup (drop tables then create them <->)

What's new

Namespace and package names Extension MUST use the type yii2-extension in composer.json file. Extension MUST NOT use yii or yii2 in the composer package name or in the namespaces used in the package. Extension SHOULD use namespaces in this format vendor-name\package (all lowercase). Extension MAY use a yii2- prefix in the composer vendor name (URL). Extension MAY use a yii2- prefix in the repository name (URL). etc...

Acceptance tests integration and examples Functional tests integration and examples Unit tests integration and examples

@cebe : I think we can close this issue now. I am done with all the system I know and can support as I am going to work with them on a regular basis. Others should be provided as extensions or by other core developers. If someone wants to start working on an implementation of an AR feel free to contact me, I can help with that.


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Easy-one-step install Redis 2.8 (latest) + PhpRedis in Ubuntu from source code

redis

Redis is a modern and very fast key-value storage. Someone calls it a "NoSQL" storage, someone - "just a memory cache". And all of them partly right - as Redis is a powerful tool, that could became very effective in different use cases.

Learn Redis

If you are not familiar with Redis at all. Start here - The Little Redis Book by Karl Seguin (Russian version)

Redis gets a lot of updates and new features, that's why in Linux repos you almost always see outdated versions. I recommend to install Redis and php_redis (PHP Redis driver extension) from source - it is very easy and fast.


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Yii2 dev digest #2 Dec'13

It has gone some time after Yii2 Alpha announce, it increased activity in GitHub issues, a lot more people have tried to touch Yii2. And this is what I have noted.

$drivers = Driver::find()->with('cars')->asArray()->all();

will get populated nested arrays with releations

 $count = Yii::$app->db->createCommand('
      SELECT COUNT(*) FROM tbl_user WHERE status=:status
  ', [':status' => 1])->queryScalar();

  $dataProvider = new SqlDataProvider([
      'sql' => 'SELECT * FROM tbl_user WHERE status=:status',
      'params' => [':status' => 1],
      'totalCount' => $count,
      'sort' => [
          'attributes' => [
              'age',
              'name' => [
                  'asc' => ['first_name' => SORT_ASC, 'last_name' => SORT_ASC],
                  'desc' => ['first_name' => SORT_DESC, 'last_name' => SORT_DESC],
                  'default' => SORT_DESC,
                  'label' => 'Name',
              ],
          ],
      ],
      'pagination' => [
          'pageSize' => 20,
      ],
  ]);

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Processing AppStore auto renewable subscriptions in PHP

in-app-purchases

First all be aware of Apple's policy as for auto renewable subscription and application types that could use it (your app could be rejected if reviewers will decide you that you are missusing subscriptions).

11.15 Apps may only use auto renewing subscriptions for periodicals (newspapers, magazines), business Apps (enterprise, productivity, professional creative, cloud storage) and media Apps (video, audio, voice), or the App will be rejected

Auto renewable subscriptions flow

Basically it works as all AppStore in-app purchases - iOS makes purchase on client side, receives Receipt and gives it server for validation. An issue appears when you need to renew subscription - unfortunately there is no something like IPN in PayPal and AppStore does not "push inform" us about prolongation or cancellation of subscription (as PayPal do). We need to do it ourselves.

As for auto-renew subscriptions we should make such steps:

  • Take initial receipt, validate it on server side (what should be validated except Apple response - is a topic for another big post)
  • Store initial receipt in DB (assign to user internally and save renew date)
  • CRON job should make periodic check of records by renew date (frequency depends on your logic, but once in 1-6 hours could be fine)
  • If it is time to check some subscription - take previously saved Receipt and make a validate request to Apple server as usually
  • If subscription was continued and money booked from user - you will receive response with new Receipt (and old one also), if not renewed - you will receive "Expired" response.
  • If subscription was continued and success response received - save it to DB, and use in next subscription validation round
  • If not - process your app logic on expired subscription (close some services for this user or something)

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Ievgen
Kuzminov "iJackUA"
Web Team Lead
at MobiDev (Kharkiv, Ukraine)
Code in Ruby and Elixir, but still love PHP. Explore ES6 and Vue.js. Explore databases, use Ubuntu and MacOS, think about IT people and management

Notes


Have you noticed? Nowadays nobody is doing a New JavaScript framework 😧 These days are over... Everybody is doing their brand new blockchain 😜