Persistent Caches - when do the contents get written.

[John Ament]

I have the following cache configuration, which is pretty much verbatim from the sample files

I'm trying to figure out though, when do the cache contents get written to disk?

{code:xml}<namedCache name="persistentCache">

      <!--

            Cache loaders.

 
            If passivation is enabled, state is offloaded to the cache loaders ONLY when evicted.  Similarly, when the state

            is accessed again, it is removed from the cache loaderold and loaded into memory.

 
            Otherwise, state is always maintained in the cache loaderold as well as in memory.

 
            Set 'shared' to true if all instances in the cluster use the same cache loaderold instance, e.g., are talking to the

            same database.

 
            If "preload" is true, all keys are loaded from the cache loaderold into memory upon starting the cache.

         -->

      <loaders passivation="true" shared="false" preload="true">

 
         <!--

            We can have multiple cache loaders, which get chained

         -->

         <loader class="org.infinispan.loaders.file.FileCacheStore" fetchPersistentState="true"

                 ignoreModifications="true" purgeOnStartup="false">

 
            <!-- See the documentation for more configuration examples and flags. -->

            <properties>

               <property name="location" value="/ssg/scorecard"/>

            </properties>

            <singletonStore enabled="true" pushStateWhenCoordinator="true" pushStateTimeout="20000"/>

            <async enabled="true" flushLockTimeout="15000" threadPoolSize="5"/>

         </loader>

      </loaders>

 
      <deadlockDetection enabled="true" spinDuration="1000"/>

 
   </namedCache>{code}

[Amin Abbaspour]

Since your store is configured as async with threadPool size 5, it means that there are five threads apart from main thread waiting to sync modification to store.

If your cache store is fast enough this means almost sync with rate of change, but if not, then changes get aggregate and the very last value of modified keys is synced whenever one of threads becomes available. https://jira.jboss.org/jira/browse/ISPN-116

Have a look at this too: http://community.jboss.org/wiki/Write-ThroughAndWrite-BehindCaching

[Amin Abbaspour]

btw there is this issue in the current release which may affect store process but is in progress https://jira.jboss.org/jira/browse/ISPN-340

[John Ament]

so as far as I'm concerned, writing synchronously is fine.  the way the app will work, an offline process (ejb timer) will populate the cache, probably only once or twice in the next 6 weeks or so. that part's fine.

The only part i had to change was the loaders config.

    <loaders passivation="true" shared="false" preload="true">

[John Ament]

So i'm still running into something weird.

Now, I'm running on my linux laptop.  It was working fine, but now I've noticed that after restarting the app server (glassfish) contents get deleted but not readded.  after modifying the values again, I don't see the new writes.

Here's my configuration:

{code:xml}  <namedCache name="persistentCache">
    <loaders passivation="true" shared="false" preload="true">
      <loader 
          class="org.infinispan.loaders.file.FileCacheStore" 
          fetchPersistentState="true" ignoreModifications="false"
          purgeOnStartup="false">
        <properties>
          <property name="location" value="/dumps/cache"/>
        </properties>
      </loader>
    </loaders>
  </namedCache>{code}

I use a JSF front end and CDI to work with the actions.  Here's some code:

{code}@SessionScoped @Named("addCacheAction")
public class AddCacheAction implements java.io.Serializable{
    private InputForm inputForm = new InputForm();
    @EJB Initializer init;

    public InputForm getInputForm() {
        return inputForm;
    }

    public void setInputForm(InputForm inputForm) {
        this.inputForm = inputForm;
    }

    public String addToCache() {
        Cache<String,String> cache = init.getCache("persistentCache");
        cache.put(inputForm.getKey(), inputForm.getValue());
        inputForm = new InputForm();
        return "/main.xhtml";
    }

    @Produces @Named("cacheList") @RequestScoped
    public List<String> produceCacheList() {
        Cache<String,String> cache = init.getCache("persistentCache");
        List<String> values = new ArrayList<String>();
        Set<Map.Entry<String,String>> entries = cache.entrySet();
        for(Map.Entry<String,String> entry : entries) {
            values.add(String.format("%s : %s",entry.getKey(),entry.getValue()));
        }
        return values;
    }

}{code}

[John Ament]

so it seems like the issue is related to having both passivation and preload set to true.  What is passivation supposed to do?  I figured it had to do with writing the cache.

[Manik Surtani]

I just added a FAQ to answer your question. 

http://community.jboss.org/wiki/infinispantechnicalfaqs#What_does_the_passivation_flag_do

[Amin Abbaspour]

This link is also concise and helpful: http://docs.jboss.org/infinispan/4.0/apidocs/config.html