我有以下代码使用cassandra python驱动程序进行分页
我尝试了覆盖查询并设置会话default_fetch_size。但是它们都没有工作,结果始终是表中的所有行。我错过了什么?
from cassandra.cluster import Cluster
from cassandra.query import SimpleStatement
# setup
cluster = Cluster(["10.40.10.xxx","10.40.10.xxx","10.40.22.xxx","10.40.22.xxx"])
session = cluster.connect()
session.set_keyspace("ad_realtime")
# session.default_fetch_size = 10
query = "SELECT * from campaign_offset"
statement = SimpleStatement(query, fetch_size=10)
results = session.execute(statement)
for row in results:
print row
答案 0 :(得分:1)
在Python驱动程序中进行分页并不意味着只获取部分查询。这意味着一次只能获取部分查询。
您的代码
for row in results:
print row
正在调用分页机制。基本上这是创建一个迭代器,它一次只能从查询定义的结果集中请求fetch_size
行。
使用LIMIT
和WHERE
条款来限制您的实际结果。
cassandra pagination: the difference between driver and CQL
答案 1 :(得分:0)
您可以使用current_rows
获取当前页面的行,例如:
for row in results.current_rows:
print row
答案 2 :(得分:0)
以下代码可以帮助您以分页的方式获取结果-
def fetch_rows(stmt: Statement, fetch_size: int = 10):
stmt.fetch_size = fetch_size
rs: ResultSet = session.execute(stmt)
has_pages = rs.has_more_pages
while has_pages:
yield from rs.current_rows
print ('-----------------------------------------')
has_pages = rs.has_more_pages
rs = session.execute(ps, paging_state=rs.paging_state)
def execute():
query = "SELECT col1, col2 FROM my_table WHERE some_partition_key='part_val1' AND some_clustering_col='clus_val1'"
ps = session.prepare(query)
for row in fetch_rows(ps, 20):
print(row)
# Process the row and perform desired operation