python cql 驱动 - cassandra.ReadTimeout - "操作超时 - 仅收到1个响应。

Question

我正在使用Cassandra 2.0和Python的CQL。

我创建了一个列族，具体如下：

CREATE KEYSPACE IF NOT EXISTS Identification
  WITH REPLICATION = { 'class' : 'NetworkTopologyStrategy',
  'DC1' : 1 };

USE Identification;

CREATE TABLE IF NOT EXISTS entitylookup (
  name varchar,
  value varchar,
  entity_id uuid,
  PRIMARY KEY ((name, value), entity_id))
WITH
    caching=all
;

然后我尝试计算这个列族中的记录数量，方法如下：

#!/usr/bin/env python
import argparse
import sys
import traceback
from cassandra import ConsistencyLevel
from cassandra.cluster import Cluster
from cassandra.query import SimpleStatement

def count(host, cf):    
    keyspace = "identification"
    cluster = Cluster([host], port=9042, control_connection_timeout=600000000)
    session = cluster.connect(keyspace)
    session.default_timeout=600000000

    st = SimpleStatement("SELECT count(*) FROM %s" % cf, consistency_level=ConsistencyLevel.ALL)
    for row in session.execute(st, timeout=600000000):
        print "count for cf %s = %s " % (cf, str(row))
    dump_pool.close()
    dump_pool.join()

if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("-cf", "--column-family", default="entitylookup", help="Column Family to query")
    parser.add_argument("-H", "--host", default="localhost", help="Cassandra host")    
    args = parser.parse_args()

    count(args.host, args.column_family)

    print "fim"

这个计数对我来说并没有太大用处，只是一个测试，而这个操作需要很长时间才能完成。

虽然我把超时时间设置为600000000秒，但不到30秒我就收到了以下错误：

./count_entity_lookup.py  -H localhost -cf entitylookup 
    Traceback (most recent call last):
      File "./count_entity_lookup.py", line 27, in <module>
        count(args.host, args.column_family)
      File "./count_entity_lookup.py", line 16, in count
        for row in session.execute(st, timeout=None):
      File "/home/mvalle/pyenv0/local/lib/python2.7/site-packages/cassandra/cluster.py", line 1026, in execute
        result = future.result(timeout)
      File "/home/mvalle/pyenv0/local/lib/python2.7/site-packages/cassandra/cluster.py", line 2300, in result
        raise self._final_exception
    cassandra.ReadTimeout: code=1200 [Timeout during read request] message="Operation timed out - received only 1 responses." info={'received_responses': 1, 'data_retrieved': True, 'required_responses': 2, 'consistency': 5}

看起来答案只在一个副本中找到了，但这对我来说真的不太合理。难道Cassandra就不能查询到它吗？

在下面的图片中，可以看到对集群的请求量非常少，延迟也很低。我不太确定为什么会这样。

在这里输入图片描述

数据库性能超时设置 cassandra 列族 cql readtimeout 副本查询集群请求

python cql 驱动 - cassandra.ReadTimeout - "操作超时 - 仅收到1个响应。

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