Echache 3.2.0 No Store.Provider found to handle configured resource types [offheap, disk] exception - ehcache

Question

i have recently switched from an older implementation of ehcache to version 3.2 so i have the following xml configuration file for a project:
<eh:config xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
xmlns:eh='http://www.ehcache.org/v3'
xsi:schemaLocation="http://www.ehcache.org/v3
http://www.ehcache.org/schema/ehcache-core-3.0.xsd">
<eh:persistence directory="C:\foo\bar\Cache-Persistence"/>
<eh:thread-pools>
<eh:thread-pool alias="defaultDiskPool" min-size="1" max-size="3"/>
</eh:thread-pools>
<eh:disk-store thread-pool="defaultDiskPool"/>
<eh:cache-template name="PROC_REQTemplate">
<eh:key-type>java.lang.String</eh:key-type>
<eh:value-type>java.lang.String</eh:value-type>
<eh:expiry>
<eh:ttl>640</eh:ttl>
</eh:expiry>
<eh:resources>
<eh:offheap unit="MB">500</eh:offheap>
<eh:disk unit="GB" persistent="true">3</eh:disk>
</eh:resources>
<eh:disk-store-settings thread-pool="defaultDiskPool"/>
</eh:cache-template>
<eh:cache alias="proc_req_cache" uses-template="PROC_REQTemplate"/>
</eh:config>
with the above shown configuration i get the following exception trace that i keep truncated to conserve a bit of space but shows clearly the error:
java.lang.IllegalStateException: No Store.Provider found to handle configured resource types [offheap, disk] from {org.ehcache.impl.internal.store.heap.OnHeapStore$Provider, org.ehcache.impl.internal.store.tiering.TieredStore$Provider, org.ehcache.impl.internal.store.offheap.OffHeapStore$Provider, org.ehcache.impl.internal.store.disk.OffHeapDiskStore$Provider}
at org.ehcache.core.internal.store.StoreSupport.selectStoreProvider(StoreSupport.java:80) ~[?:?]
at org.ehcache.core.EhcacheManager.getStore(EhcacheManager.java:440) ~[?:?]
at org.ehcache.core.EhcacheManager.createNewEhcache(EhcacheManager.java:311) ~[?:?]
at org.ehcache.core.EhcacheManager.createCache(EhcacheManager.java:260) ~[?:?]
at org.ehcache.core.EhcacheManager.init(EhcacheManager.java:567) ~[?:?]
I thought that according to the current 3.2 documentation you can use any combination of data storage tiers but apparently this is not the case as the above error shows.So...
I can only make the above hown configuration to work if i comment-out the
offheap resource and leave only the disk but not both. Is this normal? what am i missing?
As per the 2.7.8 version the documentation (see here ehcache-2.8-storage-options) mentioned BigMemory as the offHeap store however, in ehcache-3.2.0.jar if i am seeing correctly there is some-kind of internal map for that purpose. Could the error reported above be related to the fact that i am not including BigMemory in the project? My guess is no, but it would be nice if someone could clarify?
Any help would be greatly appreciated. Thanks in advance.

Answer 1

In short, there is currently no support for having a disk tier with just an offheap tier. The current Ehcache 3.x support for tiering mandates a heap tier the moment you want to have multiple tiers.
Supported combination at this day (Ehcache 3.1.x and above):
heap or offheap or disk or clustered (single tier)
heap + offheap
heap + disk
heap + offheap + disk
heap + clustered
heap + offheap + clustered
The error has nothing to do with BigMemory which was the commercial offering on top of Ehcache 2.x.

Answer 2

The problem is that the higher caching level (currently offheap) needs to be a caching tier (our terminology for near caching). Right now, offheap isn't. So you need an onheap level as soon as you start having layers. Here is a working configuration.
I've also set ehcache as default namespace to make the xml more readable. And set the defaultThreadPool as default to prevent you from having to set it everywhere (and alternative is to add <event-dispatch thread-pool="defaultDiskPool"/> because the event-dispatch needs a thread pool and there was no default).
<config xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
xmlns='http://www.ehcache.org/v3'
xsi:schemaLocation="http://www.ehcache.org/v3
http://www.ehcache.org/schema/ehcache-core-3.0.xsd">
<persistence directory="C:\foo\bar\Cache-Persistence"/>
<thread-pools>
<thread-pool alias="defaultDiskPool" min-size="1" max-size="3" default="true"/>
</thread-pools>
<cache-template name="PROC_REQTemplate">
<key-type>java.lang.String</key-type>
<value-type>java.lang.String</value-type>
<expiry>
<ttl>640</ttl>
</expiry>
<resources>
<heap unit="entries">1</heap>
<offheap unit="MB">500</offheap>
<disk unit="GB" persistent="true">3</disk>
</resources>
</cache-template>
<cache alias="proc_req_cache" uses-template="PROC_REQTemplate"/>
</config>