GH#2256 Introduce a query optimizer concept

rdflib/plugins/sparql/optimizer.py

@@ -0,0 +1,46 @@
+from __future__ import annotations
+
+"""
+This contains standard optimizers for sparql
+
+"""
+import re
+from rdflib import Literal
+from rdflib.plugins.sparql.operators import Builtin_CONTAINS, Builtin_REGEX
+from rdflib.plugins.sparql.sparql import Query
+from rdflib.plugins.sparql.algebra import CompValue, Join, Values, Expr
+from typing import Any
+
+"""
+An interface for having optimizers that transform a query algebra hopefully
+in an faster to evaluate version.
+"""
+
+
+class SPARQLOptimizer:
+    def optimize(self, query: Query) -> Query:
+        return query
+
+
+class ValuesToTheLeftOfTheJoin(SPARQLOptimizer):
+
+    def optimize(self, query: Query) -> Query:
+        main = query.algebra
+        query.algebra = self._optimize_node(main)
+        return query
+
+    def _optimize_node(self, cv: Any) -> Any:
+        if cv.name == "Join":
+            if cv.p1.name != "ToMultiSet" and "ToMultiSet" == cv.p2.name:
+                cv.update(p1=cv.p2, p2=cv.p1)
+            else:
+                cv.update(self._optimize_node(cv.p1), self._optimize_node(cv.p2))
+            return cv
+        elif cv.p is not None:
+            cv.p.update(self._optimize_node(cv.p))
+        elif cv.p1 is not None and cv.p2 is not None:
+            cv.p1.update(self._optimize_node(cv.p1))
+            cv.p2.update(self._optimize_node(cv.p2))
+        elif cv.p1 is not None:
+            cv.p1.update(self._optimize_node(cv.p1))
+        return cv

rdflib/plugins/sparql/processor.py

@@ -10,9 +10,10 @@
 from rdflib.plugins.sparql.evaluate import evalQuery
 from rdflib.plugins.sparql.parser import parseQuery, parseUpdate
 from rdflib.plugins.sparql.sparql import Query
+from rdflib.plugins.sparql.optimizer import SPARQLOptimizer
 from rdflib.plugins.sparql.update import evalUpdate
 from rdflib.query import Processor, Result, UpdateProcessor
-
+from typing import List
 
 def prepareQuery(queryString, initNs={}, base=None) -> Query:
     """
@@ -63,8 +64,9 @@ def update(self, strOrQuery, initBindings={}, initNs={}):
 
 
 class SPARQLProcessor(Processor):
-    def __init__(self, graph):
+    def __init__(self, graph, optimizers: List[SPARQLOptimizer] = None):
         self.graph = graph
+        self.optimizers = optimizers
 
     def query(self, strOrQuery, initBindings={}, initNs={}, base=None, DEBUG=False):
         """
@@ -78,4 +80,8 @@ def query(self, strOrQuery, initBindings={}, initNs={}, base=None, DEBUG=False):
             query = translateQuery(parsetree, base, initNs)
         else:
             query = strOrQuery
+
+        for optimizer in self.optimizers:
+            query = optimizer.optimize(query)
+
         return evalQuery(self.graph, query, initBindings, base)

test/test_sparql/test_optimizers.py

@@ -0,0 +1,70 @@
+from rdflib import Graph
+from rdflib.plugins.sparql.parser import *
+# from rdflib.plugins.sparql.processor import prepareQuery
+from rdflib.plugins.sparql.processor import translateQuery
+from rdflib.plugins.sparql.processor import parseQuery
+from rdflib.plugins.sparql.optimizer import ValuesToTheLeftOfTheJoin, RegexAsStringFunctionsOptimizer
+
+query_slow = """
+PREFIX ex:<https://example.org/>
+
+SELECT ?x {
+  ?x ?y ?z .
+  VALUES (?x) {
+    (ex:1)
+    (ex:2)
+    (ex:3)
+  }
+}
+"""
+
+query_fast = """
+PREFIX ex:<https://example.org/>
+
+SELECT ?x {
+  VALUES (?x) {
+    (ex:1)
+    (ex:2)
+    (ex:3)
+  }
+    ?x ?y ?z .
+}
+"""
+
+query_regex = """
+PREFIX ex:<https://example.org/>
+
+SELECT ?x {
+  ?x ?y ?z .
+  FILTER(regex("?z", "hi"))
+}
+"""
+
+query_contains = """
+PREFIX ex:<https://example.org/>
+
+SELECT ?x {
+  ?x ?y ?z .
+  FILTER(contains("?z", "hi"))
+}
+"""
+
+
+def test_values_to_left():
+    qs = _prepare_query(query_slow)
+    qf = _prepare_query(query_fast)
+    assert qs != qf
+    qso = ValuesToTheLeftOfTheJoin().optimize(qs)
+
+    assert qso.algebra == qf.algebra
+
+
+def _prepare_query(str_or_query):
+    parse_tree = parseQuery(str_or_query)
+    query = translateQuery(parse_tree, None, {})
+    return query
+
+
+if __name__ == "__main__":
+    test_values_to_left()
+