public class ASTStaticBindingsOptimizer extends Object implements IASTOptimizer
Optimizer that aims at the optimization of SPARQL 1.1 pattern detecting static (i.e., non runtime dependent) binding for variables, moving them to the top-level of the query where possible, and attaching them with occurrences of the variable.
The optimizer may apply to the following construct:
(A) BIND + VALUES clauses with constant values;
(B) FILTER IN clauses with URIs;
(C) FILTERs with sameTerm(?x,
It proceeds as follows:
1. Identify the constructs mentioned above in the query and record identified
static bindings. We distinguish between produced static bindings, namely
constructs that introduce bindings (case A above) and enforced static
bindings (cases B and C) above. Produced bindings are recorded in class
ASTStaticBindingsOptimizer.StaticBindingInfo, and for them we also remove the construct
producing the bindings, as they will later be added to as static bindings
to the query top level (see step 3a below). See step 3b below for the
treatment of enforced bindings
2. Along the way, we record usages of all variables, see class
ASTStaticBindingsOptimizer.VariableUsageInfo. These usages (i) may be used for inlining
in a later step, whenever we detected static bindings and (b) are used
to decide whether static bindings can be considered global. There are
some pitfalls here, in particular with FILTER expressions, see the code
for in-depth comments.
3. Having extracted the static bindings and the associated variable usages, we proceed as follows: 3a. Produced bindings are moved to the top-level. For the main query this means inserting them into the set of exogeneous bindings, for subqueries we construct a VALUES clause. 3b. Both the produced and enforced bindings are "inlined" to identified usages of the variable. This essentially means replacing occurrences of the variable through a hybrid of Variable+Constant. This info can then later be used in further optimization steps and at runtime.
4. As a side effect, the optimizer re-initializes the
class with the statically known bindings for the top-level query, which
againg may be valuable input for further optimization.
Note: This optimizer generalizes the
ASTValuesOptimizer, and the
have been disabled and marked deprecated
The following extensions are not considered crucial for now, but might be
subject to future work on this optimizer: (i) we may want to decompose
FILTERs prior to running this optimizer, which may be useful to identify;
(ii) in some cases it is also valid to propagate static bindings to
optional patterns; implementing this might increase the benefit of the
optimizer; (iii) we could implement some special handling for the variables
currently, they're just treated as "normal" variables and hence only inlined
at top-level, but it would be possible to inline them into subqueries and
in any nested scope as well, giving us a (in general) a better evaluation
|Modifier and Type||Class and Description|
Task specifying the inlining opportunities for a given variable in the form of a list of query nodes in which a statically derived value for the given variable can be inlined.
Class that helps to keep track of static bindings that have been spotted during query analysis.
Helper class used to record usage of a given variable, i.e.
|Constructor and Description|
|Modifier and Type||Method and Description|
Optimize the AST.
public QueryNodeWithBindingSet optimize(AST2BOpContext context, QueryNodeWithBindingSet input)
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