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https://issues.apache.org/jira/browse/JENA-2049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17286418#comment-17286418
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ASF subversion and git services commented on JENA-2049:
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Commit b156dedce40366a8aa05f2b56e22f736f0e464c4 in jena's branch
refs/heads/main from Andy Seaborne
[ https://gitbox.apache.org/repos/asf?p=jena.git;h=b156ded ]
Merge pull request #926 from afs/binding
JENA-2049: Binding improvements
> 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: 40m
> 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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