This is how you can write to cache - 

    Rails.cache.write(&#39;key&#39;, &#39;value&#39;, :time_to_idle =&gt; 60.seconds, :timeToLive =&gt; 600.seconds)

and in order to delete from cache you can use `delete` action - 

    Rails.cache.delete(&#39;key&#39;)

Delete multiple keys -

    Rails.cache.delete_if {|k, v| k =~ &#39;key&#39; }

To answer my own question...it seems that given I&#39;m using memcached, I actually can&#39;t use `delete_if` or `delete_matched` because memcached does not support enumerating or querying keys by pattern ([1][1]).


  [1]: https://github.com/mperham/dalli/issues/40#issuecomment-530318

You can use the https://github.com/Phobos98/dalli-delete-matched gem that adds a simple implementation of `delete_matched` method for dalli store with memcached.

Can someone post an example of how in Jersey to set `StreamingOutput` as an entity in a `Response` object?

I haven&#39;t been able to find an example of this.

Example of using StreamingOutput as Response entity in Jersey

I need to display both `icon` and `title` of action inside `ActionBar`.

I&#39;ve tried &quot;`withText`&quot; option, but it has no effect.

![enter image description here][1]


  [1]: http://i.stack.imgur.com/3N4H4.png

How to display both icon and title of action inside ActionBar?

Is it possible to somehow run `Rails.cache.clear` and only clear keys with a certain name/string?

I don&#39;t want to clear the entire cache...just keys with the string `blog/post` in the name (ie. `blog/post/1`, `blog/post/2`).

I&#39;m using [dalli][1] with memcached for my cache and running Rails 3.0.6.


  [1]: https://github.com/mperham/dalli

Rails.cache.clear certain key names?

Is it possible to somehow run <code>Rails.cache.clear</code> and only clear keys with a certain name/string?
I don't want to clear the entire cache...just keys with the string <code>blog/post</code> in the name (ie. <code>blog/post/1</code>, <code>blog/post/2</code>).
I'm using <a href="https://github.com/mperham/dalli" target="_blank" rel="noopener noreferrer">dalli</a> with memcached for my cache and running Rails 3.0.6.

According to Rails doc: http://guides.rubyonrails.org/migrations.html

&quot;Active Record tracks which migrations have already been run so all you have to do is update your source and run rake db:migrate.&quot;

How does ActiveRecord actually do this?  Where does Active Record store the data?

I suspect this might be stored in the database itself?  In a table somewhere.

On my development machine, I ran all the migrations.  Then I copied the production database over using mysqldump.  Then I ran &quot;rake db:migrate:status&quot;, it shows correctly the migrations that need to run on the production database.

I used to think that ActiveRecord keeps track of the last migration run using the timestamp.  But I think this is not true because ActiveRecord correctly runs the &quot;older&quot; migrations merged in from another code branch.

Could someone with inside knowledge of this elaborate?
Thanks

How does Rails keep track of which migrations have run for a database?

I am in an older Rails project that has a Gemfile. I tried to add a gem to the Gemfile and `bundle install` but got an error:

    Bundler could not find compatible versions for gem &quot;bundler&quot;:
      In Gemfile:
        rails (= 3.0.0) ruby depends on
          bundler (~&gt; 1.0.0) ruby
    
      Current Bundler version:
        bundler (1.1.5)
    
    This Gemfile requires a different version of Bundler.

The version of Rails it&#39;s using requires bundler ~&gt;1.0.0 but I have 1.1.5 installed and am using it for my other projects. Usually I would use `bundle exec ...` but since this is bundler we are talking about, it&#39;s a little more complicated than that. How can I add a gem to my Gemfile and run `bundle install` while using the version of bundler that it requires?


How to `bundle install` when your Gemfile requires an older version of bundler?

I have this code: 

    &lt;%= link_to image_tag(&quot;facebook.png&quot;, :class =&gt; &quot;facebook_icon&quot;, :alt =&gt; &quot;Facebook&quot;, :target =&gt; &quot;_blank&quot;),                 
                &quot;http://www.facebook.com/mypage&quot; %&gt;

How can I make it open in a new tab when a user clicks the link?

Rails: Open link in new tab (with &#39;link_to&#39;)

I have an existing form which is tied to a model named &#39;Order&#39;, but i want to add new form fields that will capture Credit Card info such as name, cc number, etc to be processed on a 3rd party payment gateway.

But since i don&#39;t want to save CC info in our database, there are no corresponding columns of that in my order table. And this gives me an error when submitting the form that those Credit card input fields are not &#39;part&#39; of the order model. 



rails simple_form fields not related to the model

Here are two sample codes.

First one with `collect`:

    User.first.gifts.collect(&amp;:id)

Second one with `pluck`:


    User.first.gifts.pluck(:id)


Is there any difference between them in performance or something else?

What is the difference between pluck and collect in Rails?

Is there a way to specify that if the method returns null value, then don&#39;t cache the result in @Cacheable annotation for a method like this?

    @Cacheable(value=&quot;defaultCache&quot;, key=&quot;#pk&quot;)
    public Person findPerson(int pk) {
       return getSession.getPerson(pk);
    }

Update:
here is the JIRA issue submitted regarding caching null value last November, which hasn&#39;t resolved yet: 
[\[#SPR-8871\] @Cachable condition should allow referencing return value - Spring Projects Issue Tracker][1]


  [1]: https://jira.springsource.org/browse/SPR-8871

How do I tell Spring cache not to cache null value in @Cacheable annotation

I&#39;m trying to call a `@Cacheable` method from within the same class:

    @Cacheable(value = &quot;defaultCache&quot;, key = &quot;#id&quot;)
    public Person findPerson(int id) {
       return getSession().getPerson(id);
    } 
    
    public List&lt;Person&gt; findPersons(int[] ids) {
       List&lt;Person&gt; list = new ArrayList&lt;Person&gt;();
       for (int id : ids) {
          list.add(findPerson(id));
       }
       return list;
    }

and hoping that the results from `findPersons` are cached as well, but the `@Cacheable` annotation is ignored, and `findPerson` method got executed everytime.

Am I doing something wrong here, or this is intended?

Spring cache @Cacheable method ignored when called from within the same class

I have an Android HTC Amaze and an Android HTC Desire. My Sencha Touch 2 apps wrapped by PhoneGap work excellent for the Desire but they refuse to load on the HTC Amaze 4.0.3.
I&#39;m getting this kind of errors in log -

    08-24 17:08:37.577: E/chromium(16106): external/chromium/net/disk_cache/stat_hub.cc:190: [0824/170837:ERROR:stat_hub.cc(190)] StatHub::Init - App &quot;appname&quot; isn&#39;t supported.

Can anybody help? 

Android - Sencha Touch 2 PhoneGap issue for 4.0.x

Since the upgrade to iOS 6, we are seeing Safari&#39;s web view take the liberty of caching `$.ajax` calls. This is in the context of a PhoneGap application so it is using the Safari WebView. Our `$.ajax` calls are `POST` methods and we have cache set to false `{cache:false}`, but still this is happening. We tried manually adding a `TimeStamp` to the headers but it did not help.

We did more research and found that Safari is only returning cached results for web services that have a function signature that is static and does not change from call to call.  For instance, imagine a function called something like:

    getNewRecordID(intRecordType)

This function receives the same input parameters over and over again, but the data it returns should be different every time.

Must be in Apple&#39;s haste to make iOS 6 zip along impressively they got too happy with the cache settings.  Has anyone else seen this behavior on iOS 6? If so, what exactly is causing it?

---

The workaround that we found was to modify the function signature to be something like this:

    getNewRecordID(intRecordType, strTimestamp)

and then always pass in a `TimeStamp` parameter as well, and just discard that value on the server side.  This works around the issue. 

Is Safari on iOS 6 caching $.ajax results?

When I visit [chesseng.herokuapp.com][1] I get a response header that looks like

    Cache-Control:private
    Connection:keep-alive
    Content-Encoding:gzip
    Content-Type:text/css
    Date:Tue, 16 Oct 2012 06:37:53 GMT
    Last-Modified:Tue, 16 Oct 2012 03:13:38 GMT
    Status:200 OK
    transfer-encoding:chunked
    Vary:Accept-Encoding
    X-Rack-Cache:miss

and then I refresh the page and get

    Cache-Control:private
    Connection:keep-alive
    Date:Tue, 16 Oct 2012 06:20:49 GMT
    Status:304 Not Modified
    X-Rack-Cache:miss

so it seems like caching is working. If that works for caching then what is the point of ***Expires*** and **Cache-Control:max-age**. To add to confusion, when I test the page at [https://developers.google.com/speed/pagespeed/insights/][2] it tells me to &quot;Leverage browser caching&quot;.


  [1]: http://chesseng.herokuapp.com
  [2]: https://developers.google.com/speed/pagespeed/insights

What is Cache-Control: private?

I&#39;m working with a couple of Web Servers behind a Load Balancer and I can enable Sticky Sessions to hold a user to the one specific Web Servers - this will work.

I have been reading about PHP Sessions &amp; MemCache. I must say what I&#39;ve read is a touch confusing as some pages say its a good idea and others the opposite.

Questions:

1. is it possible to keep php sessions in memcache?
2. is it better to use sticky sessions over memcache?
3. what are the problems with php sessions in memcache - note: I can get enough cache (amazon so its expandable).


Is it recommended to store PHP Sessions in MemCache?

Hello when I attempt to install pylibmc on OSX Lion using pip I get the following error:

    ./_pylibmcmodule.h:42:10: fatal error: &#39;libmemcached/memcached.h&#39; file not found

    #include &lt;libmemcached/memcached.h&gt;

             ^

    1 error generated.

    error: command &#39;clang&#39; failed with exit status 1

Any clues at how to solve this issue?

Error when install pylibmc using pip

How can I get all the keys set in my memcached instance(s)?

I tried googling, but didn&#39;t find much except that `PHP` supports a [`getAllKeys` method][1], which means it is actually possible to do this somehow. How can I get the same within a telnet session?

I have tried out all the retrieval related options mentioned in [memcached cheat sheet][2] and [Memcached telnet command summary][3], but none of them work and I am at a loss to find the correct way to do this.

Note: I am currently doing this in development, so it can be assumed that there will be no issues due to new keys being set or other such race conditions happening, and the number of keys will also be limited.


  [1]: http://php.net/manual/en/memcached.getallkeys.php
  [2]: http://www.lzone.de/articles/memcached.htm
  [3]: http://blog.elijaa.org/?post/2010/05/21/Memcached-telnet-command-summary

get all keys set in memcached

Redis can do everything that Memcached provides (LRU cache, item expiry, and now clustering in version 3.x+, currently in beta) or by tools like twemproxy. The performance is similar too. Morever, Redis adds persistence due to which you need not do cache warming in case of a server restart.

Reference to some old answers which compare Redis and Memcache, some of which favor Redis as replacement of Memcache (if already present in the stack):

* https://stackoverflow.com/questions/10558465/memcache-vs-redis

* https://stackoverflow.com/questions/2873249/is-memcached-a-dinosaur-in-comparison-to-redis

* https://stackoverflow.com/questions/4188620/redis-and-memcache-or-just-redis

In spite of this, on studying stacks of large web scale companies like Instagram, Pinterest, Twitter etc, I found that they use both Memcached and Redis for different purposes, not using Redis for primary caching. The primary cache is still Memcached, and Redis is used for its data structures based logical caching.

As of 2014, why is memcached still worth the pain to be added as additional component into your stack, when you already have a Redis component which can do everything that memcached can? What are the favorable points that incline the architects/engineers to still include memcached apart from already existing Redis?

# Update : 
For our platforms, we have completely discarded Memcached, and use redis for plain as well as logical caching requirements. Highly
performant, flexible and reliable.

Some example scenarios:

 - Listing all cached keys by a specific pattern, and read or delete their values. Very easy in redis, not doable ( easily ) in memcached.
 - Storing a payload more than 1mb, easy to do in redis, requires slab size tweaks in memcached, which has performance side effects of its own.
 - Easy snapshots of current cache content
 - Redis cluster is production ready as well along with language drivers,hence clustered deployment is easy too.



Content Type	Original Author	Original Content on Stackoverflow
Question	Shpigford	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Sandip Ransing	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	Shpigford	View Answer on Stackoverflow
Solution 3 - Ruby on-Rails	fkoessler	View Answer on Stackoverflow

Rails.cache.clear certain key names?

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

Solution 3 - Ruby on-Rails

How to display both icon and title of action inside ActionBar?

Example of using StreamingOutput as Response entity in Jersey

Attributions