索引与约束

Question

我正在向图表推送2K +节点和8k +边缘，这需要大约7000ms。而且，我将进一步使用100k +节点和关系。我的查询以这种方式使用合并操作：

MERGE (a:User){user:'username'}
MERGE (b:Hobby){hobby:'hobby'}
MERGE (a)-[r:Hobby]->(b)

注意：用户名和爱好是查询中的字符串

现在，我正在尝试提高查询的性能。为此，谷歌搜索后，我开始了解两种方式。

索引节点属性用户名和爱好。这样，合并操作将提升表现。
CREATE Constraint on node properties username和hobby。很多人提出这种方法。

我的问题是：

索引属性和创建约束有什么区别在房产？ Graph如何处理这些（就像它在内部做的那样）操作？
哪种方法可以改善效果？

编辑：

我的代码：

session = driver.session()
session.run('CREATE CONSTRAINT ON (u:user) ASSERT u.user IS UNIQUE')
session.run('CREATE CONSTRAINT ON (h:hobby) ASSERT h.hobby IS UNIQUE')

session.close()

def writeBatch(b):
    print("writing batch of " + str(len(b)))
    session = driver.session()
    session.run('UNWIND {batch} AS elt '+
                'MERGE (u:user{user: elt.user})'+
                'MERGE (h:hobby{hobby:elt.hobby})'+
                'MERGE (u)-[r:hobby]->(h)'
                +'', {'batch': b})
    session.close()

错误：

    Traceback (most recent call last):
  File "/Users/adaggula/Documents/workspace2/Facebook/FbNeo.py", line 145, in <module>
    userhobby.foreach(write2neo)
  File "/usr/local/spark/python/pyspark/rdd.py", line 747, in foreach
    self.mapPartitions(processPartition).count()  # Force evaluation
  File "/usr/local/spark/python/pyspark/rdd.py", line 1004, in count
    return self.mapPartitions(lambda i: [sum(1 for _ in i)]).sum()
  File "/usr/local/spark/python/pyspark/rdd.py", line 995, in sum
    return self.mapPartitions(lambda x: [sum(x)]).fold(0, operator.add)
  File "/usr/local/spark/python/pyspark/rdd.py", line 869, in fold
    vals = self.mapPartitions(func).collect()
  File "/usr/local/spark/python/pyspark/rdd.py", line 771, in collect
    port = self.ctx._jvm.PythonRDD.collectAndServe(self._jrdd.rdd())
  File "/usr/local/spark/python/pyspark/rdd.py", line 2379, in _jrdd
    pickled_cmd, bvars, env, includes = _prepare_for_python_RDD(self.ctx, command, self)
  File "/usr/local/spark/python/pyspark/rdd.py", line 2299, in _prepare_for_python_RDD
    pickled_command = ser.dumps(command)
  File "/usr/local/spark/python/pyspark/serializers.py", line 428, in dumps
    return cloudpickle.dumps(obj, 2)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 646, in dumps
    cp.dump(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 107, in dump
    return Pickler.dump(self, obj)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 224, in dump
    self.save(obj)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 562, in save_tuple
    save(element)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 199, in save_function
    self.save_function_tuple(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 236, in save_function_tuple
    save((code, closure, base_globals))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 548, in save_tuple
    save(element)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 600, in save_list
    self._batch_appends(iter(obj))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 633, in _batch_appends
    save(x)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 199, in save_function
    self.save_function_tuple(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 236, in save_function_tuple
    save((code, closure, base_globals))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 548, in save_tuple
    save(element)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 600, in save_list
    self._batch_appends(iter(obj))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 633, in _batch_appends
    save(x)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 199, in save_function
    self.save_function_tuple(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 236, in save_function_tuple
    save((code, closure, base_globals))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 548, in save_tuple
    save(element)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 600, in save_list
    self._batch_appends(iter(obj))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 633, in _batch_appends
    save(x)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 199, in save_function
    self.save_function_tuple(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 236, in save_function_tuple
    save((code, closure, base_globals))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 548, in save_tuple
    save(element)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 600, in save_list
    self._batch_appends(iter(obj))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 633, in _batch_appends
    save(x)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 199, in save_function
    self.save_function_tuple(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 236, in save_function_tuple
    save((code, closure, base_globals))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 548, in save_tuple
    save(element)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 600, in save_list
    self._batch_appends(iter(obj))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 636, in _batch_appends
    save(tmp[0])
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 199, in save_function
    self.save_function_tuple(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 236, in save_function_tuple
    save((code, closure, base_globals))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 548, in save_tuple
    save(element)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 600, in save_list
    self._batch_appends(iter(obj))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 636, in _batch_appends
    save(tmp[0])
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 193, in save_function
    self.save_function_tuple(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 241, in save_function_tuple
    save(f_globals)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 681, in _batch_setitems
    save(v)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 193, in save_function
    self.save_function_tuple(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 241, in save_function_tuple
    save(f_globals)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 686, in _batch_setitems
    save(v)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 542, in save_reduce
    save(state)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 681, in _batch_setitems
    save(v)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 524, in save_reduce
    save(args)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 548, in save_tuple
    save(element)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 600, in save_list
    self._batch_appends(iter(obj))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 636, in _batch_appends
    save(tmp[0])
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 542, in save_reduce
    save(state)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 681, in _batch_setitems
    save(v)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 542, in save_reduce
    save(state)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 681, in _batch_setitems
    save(v)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 542, in save_reduce
    save(state)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 686, in _batch_setitems
    save(v)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 542, in save_reduce
    save(state)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 681, in _batch_setitems
    save(v)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 542, in save_reduce
    save(state)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 548, in save_tuple
    save(element)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 681, in _batch_setitems
    save(v)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 315, in save_builtin_function
    return self.save_function(obj)
  File "/usr/local/spark/python/pyspark/cloudpickle.py", line 191, in save_function
    if islambda(obj) or obj.__code__.co_filename == '<stdin>' or themodule is None:
AttributeError: 'builtin_function_or_method' object has no attribute '__code__'
16/09/20 16:35:22 INFO SparkContext: Invoking stop() from shutdown hook

Answer 1

索引与约束

索引是查找索引属性具有特定值的节点的快速方法，替换所有节点的顺序扫描（而不是 O（n）算法，通常得到 O（的log（n）））。许多节点可以具有相同值的属性。

约束是一种在数据上强制执行模式的方法。 Neo4j中的节点有两种类型的约束：

财产缺失：

CREATE CONSTRAINT ON (n:Node) ASSERT n.uuid IS UNIQUE;

财产存在：

CREATE CONSTRAINT ON (n:Node) ASSERT exists(n.name);

实际上，unicity约束使用索引快速查找另一个节点是否已使用相同的值。

因此，带有unicity约束的标签在属性上也有一个索引，但是属性上带索引的标签不需要单一性。

我应该使用哪一个？

由于您使用MERGE查找或创建User和Hobby节点，因此这些属性显然是唯一的。你绝对应该使用unicity约束来强制执行模式，而不是简单地使用索引。

CREATE CONSTRAINT ON (n:User) ASSERT n.user IS UNIQUE;
CREATE CONSTRAINT ON (n:Hobby) ASSERT n.hobby IS UNIQUE;

合并查询性能 - 唯一约束或索引？

1 个答案:

索引与约束

我应该使用哪一个？