[infinispan-issues] [JBoss JIRA] (ISPN-3766) "containsKey" and "get" methods are not working properly with "putForExternalRead" during active transaction. WriteSkewException appears.

[William Burns (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-3766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12927231#comment-12927231 ] 

William Burns edited comment on ISPN-3766 at 11/27/13 4:12 PM:
---------------------------------------------------------------

It is still the expected behavior

* If I don't use "get" method everything is working ok.
It sounds like whatever method you are using doesn't detect write skews then (like #3 below)
* If cache already contains element before "get" invocation - everything is working ok
That is because the PFER doesn't actually modify the value since it is a putIfAbsent call (thus no write skew occurred)
* when I use my workaround for "containsKey" functional - everything is working ok (e.g cache.keySet().contains(key))
That is because you are bypassing all write skew checks and checking the data container directly.  Which lets you do this write skew

{quote}
The problem is that I don't need to do read operation at 3, I need to check if element exists in the cache. I need a "containsKey" method, but this method has the same implementation as "get".
{quote}
That is because it also pays attention to write skews.  In your case you are trying to later modify your value in the same transaction, but another transaction has changed the value, which is a write skew (PFER has it's own transaction).
                
      was (Author: william.burns):
    It is still the expected behavior

* If I don't use "get" method everything is working ok.
It sounds like whatever method you are using doesn't detect write skews then (like #3 below)
* If cache already contains element before "get" invocation - everything is working ok
That is because the PFER doesn't actually modify the value since it is a putIfAbsent call (thus no write skew occurred)
* when I use my workaround for "containsKey" functional - everything is working ok (e.g cache.keySet().contains(key))
That is because you are bypassing all write skew checks and checking the data container directly.  Which lets you do this write skew

{quote}
The problem is that I don't need to do read operation at 3, I need to check if element exists in the cache. I need a "containsKey" method, but this method has the same implementation as "get".
{quote}
That is because it also pays attention to write skews.  In your case you are trying to later modify your value in the same transaction, but another transaction has changed the value (write skew) in another transaction (PFER has it's own transaction).
                  
> "containsKey" and "get" methods are not working properly with "putForExternalRead" during active transaction. WriteSkewException appears.
> -----------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: ISPN-3766
>                 URL: https://issues.jboss.org/browse/ISPN-3766
>             Project: Infinispan
>          Issue Type: Bug
>          Components: Transactions
>    Affects Versions: 5.3.0.Final, 6.0.0.CR1, 6.0.0.Final
>            Reporter: V L
>            Assignee: Mircea Markus
>         Attachments: InfinispanTest.java
>
>
> I'm not new with Infinispan, we use it from 5.3 version. Now I'm working on adding WriteSkew functional to our project, but unfortunately it's not working as we expected.
> We use infinispan like a cache for mongoDb data source, but this situation doesn't depends on data source vendor.
> The problem is that WriteSkewException is available in specific situation, here are steps for reproducing:
> 1) begin tx -> create an new element -> commit tx. 
> 2) wait until cache expires. cache is empty now
> 3) being tx -> try to get element from cache, but it's not found -> load element from data source -> put it to the cache via putForExternalRead for read access outside of current transaction.
> 4) make some modification with element -> put element to cache -> commit tx -> WriteSkewException
> here is my log:
> TX BEGIN tx_status=6 thread=1
> PUT id=key1, tx_status=0, thread=1 cache_size=1, cache_ contains=key:key1, value:value
> TX COMMIT tx_status=0 thread=1
> TX BEGIN. tx_status=6, thread=1
> SIZE id=key1 tx_status=0, thread=1 cache_size=1 contains=key:key1, value:null
> PUT_FOR_EXTERNAL_READ id=key1, tx_status=0 thread=1 cache_size=1 cache_contains=key:key1, value:null
> PUT id=key1 tx_status=0 thread=1 cache_size=1 contains=key:key1, value:value
> TX COMMIT status=0 thread=1
> ISPN000005: Detected write skew on key [1]. Another process has changed the entry since we last read it! Unable to copy entry for update.
> Exception executing call org.infinispan.transaction.WriteSkewException: Detected write skew.
> I think I found the problem is in "get" method. When you invoke "get" method with key that not available in cache, infinispan create an "null" element in cache. This element won't be updated by putForExternalRead method (look at log above). If you skip "get" method invocation everithing will work fine. By the way, everithing is working fine if you skip "step 2" of the scenario.
> I use workaround for this situation. I check if element exist in the cache not by "containsKey" or "get" method but via cache.keySet().contains(key)
> This works ok
> I'm looking forward for you comments, maybe I'm doing something wrong.
> Thanks

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira