[jira] [Resolved] (JENA-2049) Binding Improvements

["Andy Seaborne (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/JENA-2049?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andy Seaborne resolved JENA-2049.
---------------------------------
    Resolution: Done

> Binding Improvements
> --------------------
>
>                 Key: JENA-2049
>                 URL: https://issues.apache.org/jira/browse/JENA-2049
>             Project: Apache Jena
>          Issue Type: Improvement
>          Components: ARQ
>            Reporter: Andy Seaborne
>            Assignee: Andy Seaborne
>            Priority: Major
>             Fix For: Jena 4.0.0
>
>          Time Spent: 50m
>  Remaining Estimate: 0h
>
> {{Binding}} is a map from variables to nodes used in query processing. It is  central to execution of SPARQL.
> h3. Context
> One feature is that binding objects form a tree. To add variables to an existing  binding, whether a join or assignment (BIND), a new binding object is created with the original as parent. This avoid copy costs. The parent can be shared across solutions.
> This design leads to large numbers of {{Binding}} objects, the majority of which are quite small (1 or 2 variables).
> h3. Current Situation
> For general building, the binding implementation is the general {{BindingMap}}. This is used a lot because the number of variables is not easy to determine at the time the {{Binding}} object is allocated.
> {{Binding1}} is the special case of one var/node pair. This "one slot" binding requires the application to know there will be only one slot binding so it has limited use.
> {{BindingMap}} is not immutable, although as a {{Binding}} the mutable
>  operations need to be accessed with a cast.
> {{BindingMap}} is implemented using a Map ({{HashMap}}) with a special case of a
>  binding of one slot.
> Maps are several java object including a array. It is quite large and Java objects require initialization. For streaming queries, the total footprint is quite low; the GC will reclaim space as results rows are finished with. For queries that accumulate results (e.g general sort), bindings are held for a period of time.
> h3. Proposal
>  * A builder pattern to accumulate "(var,node)" pairs during a constriction phase before a build step that can then choose the most appropriate immutable {{Binding}} implementation.
>  This takes the work of selecting the right binding implementation off the
>  rest of the code.
>  * Expand the number fixed length bindings: Special cases for 0, 1, 2, 3, and 4 pairs.
>  * The builder can be reused (same thread) so the cost of object creation for the builder
>  can be amortized.
>  * Truly immutable bindings for long term stability.
> h3. Compatibility
> Retain, marked deprecated, the {{BindingFactory}} methods to create a {{BindingMap}} so existing code continues as before, with deprecation to indicate it would be a good idea to switch to the new way.
> h3. Non-goal
> This is not a speed up (nor a slow down).



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