.. _`DLite Durability Service`:

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DLite Durability Service
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DLite is the next generation improved durability service that complies with DDS Persistence Profile. 
DLite has a more fundamental approach of maintaining eventual consistency by two way trivial merging of data. 
This results in a better performance, scalability and out of the box experience. 
DLite can be configured instead of the existing Durability service. 

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Improvements in DLite
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* Improved scalability 
	* Implement differential alignment  
	* Support eavesdropping on alignment 
	* Implement alignment scheduling 

* Improved configuration 
	* better structured and well defined defaults. 
	* better consistency by keeping deceased instances by default 
	* global decoupling by Interest based alignment and provisioning 

* Improved maintainability and functionality 
	* Topic based control and monitoring 
	* Code and complexity reduction 
	
* Improved Scalability and stress testing 

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Migration Impact
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* Durability Dependencies instead of a Master Durability service
* Affects persistent data set selection
* Affects waitForHistoricalData
* More flexibility
* Local interest scopes instead of globally defined Namespaces
* Replaces merge policies
* Replaces aligner, alignee and durability policies 

A basic migration tool that allows the import of old durability stores is available, see
:ref:`durability_migrate: Durability to DLite Migration`.

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Wait for historical data
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The behaviour of the wait_for_historical_data operation behaves similar as before, meaning that it will wait until the state of all alive fellows is aligned. 

However for DLite this operation has some additional features: 

* it can also wait for configured dependencies. A dependency is a fellow that must be available, when not the wait_for_historical_data will not return. 

* it can be used continuously, meaning that it will block during alignment when new fellows join the network. 


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Configuration
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There is a detailed description of the available configuration parameters and their purpose in the  :ref:`Configuration <Configuration>` section, starting at the section on ``//OpenSplice/DLite``.

.. EoF