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CachingExpandInto.scala
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CachingExpandInto.scala
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/*
* Copyright (c) 2002-2017 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.cypher.internal.compatibility.v3_3.runtime.pipes
import org.neo4j.cypher.internal.compatibility.v3_3.runtime.ExecutionContext
import org.neo4j.cypher.internal.frontend.v3_3.{InternalException, SemanticDirection}
import org.neo4j.cypher.internal.spi.v3_3.QueryContext
import org.neo4j.helpers.collection.PrefetchingIterator
import org.neo4j.kernel.impl.util.ValueUtils
import org.neo4j.values.AnyValue
import org.neo4j.values.storable.Values.NO_VALUE
import org.neo4j.values.virtual.{EdgeValue, NodeValue}
import scala.collection.JavaConverters._
import scala.collection.mutable
import scala.collection.mutable.ArrayBuffer
/**
* Used by pipes that needs to expand between two known nodes.
*
* Given a pattern (a)-->(b) it will do the following:
* - if both a and b are dense nodes, start from the one with the lesser degree
* - if just one of the nodes is dense, start from the non-dense node
* - if both are non-dense, randomly pick one or the other
* - cache all found connecting relationships.
*
*/
trait CachingExpandInto {
/**
* Finds all relationships connecting fromNode and toNode.
*/
protected def findRelationships(query: QueryContext, fromNode: NodeValue, toNode: NodeValue,
relCache: RelationshipsCache, dir: SemanticDirection, relTypes: => Option[Array[Int]]): Iterator[EdgeValue] = {
val fromNodeIsDense = query.nodeIsDense(fromNode.id())
val toNodeIsDense = query.nodeIsDense(toNode.id())
//if both nodes are dense, start from the one with the lesser degree
if (fromNodeIsDense && toNodeIsDense) {
//check degree and iterate from the node with smaller degree
val fromDegree = getDegree(fromNode, relTypes, dir, query)
if (fromDegree == 0) {
return Iterator.empty
}
val toDegree = getDegree(toNode, relTypes, dir.reversed, query)
if (toDegree == 0) {
return Iterator.empty
}
relIterator(query, fromNode, toNode, preserveDirection = fromDegree < toDegree, relTypes, relCache, dir)
}
// iterate from a non-dense node
else if (toNodeIsDense)
relIterator(query, fromNode, toNode, preserveDirection = true, relTypes, relCache, dir)
else if (fromNodeIsDense)
relIterator(query, fromNode, toNode, preserveDirection = false, relTypes, relCache, dir)
//both nodes are non-dense, choose a random starting point
else
relIterator(query, fromNode, toNode, alternate(), relTypes, relCache, dir)
}
private var alternateState = false
private def alternate(): Boolean = {
val result = !alternateState
alternateState = result
result
}
private def relIterator(query: QueryContext, fromNode: NodeValue, toNode: NodeValue, preserveDirection: Boolean,
relTypes: Option[Array[Int]], relCache: RelationshipsCache, dir: SemanticDirection) = {
val (start, localDirection, end) = if(preserveDirection) (fromNode, dir, toNode) else (toNode, dir.reversed, fromNode)
val relationships = query.getRelationshipsForIds(start.id(), localDirection, relTypes).map(ValueUtils.fromRelationshipProxy)
new PrefetchingIterator[EdgeValue] {
//we do not expect two nodes to have many connecting relationships
val connectedRelationships = new ArrayBuffer[EdgeValue](2)
override def fetchNextOrNull(): EdgeValue = {
while (relationships.hasNext) {
val rel = relationships.next()
val other = rel.otherNode(start)
if (end == other) {
connectedRelationships.append(rel)
return rel
}
}
relCache.put(fromNode, toNode, connectedRelationships, dir)
null
}
}.asScala
}
private def getDegree(node: NodeValue, relTypes: Option[Array[Int]], direction: SemanticDirection, query: QueryContext) = {
relTypes.map {
case rels if rels.isEmpty => query.nodeGetDegree(node.id(), direction)
case rels if rels.length == 1 => query.nodeGetDegree(node.id(), direction, rels.head)
case rels => rels.foldLeft(0)(
(acc, rel) => acc + query.nodeGetDegree(node.id(), direction, rel)
)
}.getOrElse(query.nodeGetDegree(node.id(), direction))
}
@inline
protected def getRowNode(row: ExecutionContext, col: String): AnyValue = {
row.getOrElse(col, throw new InternalException(s"Expected to find a node at $col but found nothing")) match {
case n: NodeValue => n
case NO_VALUE => NO_VALUE
case value => throw new InternalException(s"Expected to find a node at $col but found $value instead")
}
}
protected final class RelationshipsCache(capacity: Int) {
val table = new mutable.OpenHashMap[(Long, Long), Seq[EdgeValue]]()
def get(start: NodeValue, end: NodeValue, dir: SemanticDirection): Option[Seq[EdgeValue]] = table.get(key(start, end, dir))
def put(start: NodeValue, end: NodeValue, rels: Seq[EdgeValue], dir: SemanticDirection) = {
if (table.size < capacity) {
table.put(key(start, end, dir), rels)
}
}
@inline
private def key(start: NodeValue, end: NodeValue, dir: SemanticDirection) = {
// if direction is BOTH than we keep the key sorted, otherwise direction is important and we keep key as is
if (dir != SemanticDirection.BOTH) (start.id, end.id())
else {
if (start.id() < end.id())
(start.id(), end.id())
else
(end.id(), start.id())
}
}
}
}