[infinispan-issues] [JBoss JIRA] (ISPN-1705) DummyXid should use a better implementation for generating branch and transaction identifiers

[Galder Zamarreño (JIRA)]

     [ https://issues.jboss.org/browse/ISPN-1705?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Galder Zamarreño updated ISPN-1705:
-----------------------------------

        Status: Resolved  (was: Pull Request Sent)
    Resolution: Done

    
> DummyXid should use a better implementation for generating branch and transaction identifiers
> ---------------------------------------------------------------------------------------------
>
>                 Key: ISPN-1705
>                 URL: https://issues.jboss.org/browse/ISPN-1705
>             Project: Infinispan
>          Issue Type: Bug
>          Components: Transactions
>    Affects Versions: 5.1.0.CR3
>            Reporter: Manik Surtani
>            Assignee: Manik Surtani
>            Priority: Critical
>             Fix For: 5.1.0.FINAL
>
>
> In 5.1.0, the DummyXid was modified to use UUIDs to generate full branch and transaction identifiers.  The most and least significant longs of each UUID was used to populate a part of a 64-byte array (the rest of the array being set to 0).
> This poses a number of problems.
> 1.  Generating 2 UUIDs for each XID is expensive
> 2.  Most of the 64-byte array is set to 0 and wasted
> 3.  XID.hashcode() is implemented by performing Arrays.hashcode on each of the (mostly-empty) 64-bit arrays
> This makes using the DummyTransactionManager (and consequently, the BatchModeTransactionManager) extremely efficient - if XA compliant.
> This JIRA proposes to change this such that:
> 1.  Each transaction manager creates a single UUID as a transaction manager ID
> 2.  Each XID created uses an atomic long for transaction and branch ID
> 3.  Combining most and least significant long of the transaction manager ID with the long counter can provide both transaction and branch identifiers.
> 4.  Hashcode should be calculated on the above 3 longs ONLY, not the full array, and should be cached.

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