Cassandra OperationTimedOut [英] Cassandra OperationTimedOut

问题描述

从my_table中选择计数（*）给我 OperationTimedOut：errors = {}，last_host = 127.0.0.1

select count (*) from my_table gives me OperationTimedOut: errors={}, last_host=127.0.0.1

我已经尝试在cqlshrc.sample中更改cassandra.yaml中的 request_timeout_in_ms 和 request_timeout 中的值。 （两者都在C：\Programs\DataStax-DDC\apache-cassandra\conf）但是没有成功。

I have already tried to change the values in request_timeout_in_ms in cassandra.yaml and request_timeout in cqlshrc.sample. (Both are in C:\Programs\DataStax-DDC\apache-cassandra\conf) But without success.

如何增加超时？ p>

How can I increse timeout?

推荐答案

select count（*）不是你的想法。它实际上是昂贵的，因为它一行一行计数。您可以使用带有计数器的单独列族跟踪记录数，您需要为每个在表中执行的插入操作增加记录数。例如

select count (*) is not doing what you think. It is actually expensive as it counts the rows one by one. You can track number of records using a separate column family with a counter, which you will need to increment for every insert you do into your table. For example

CREATE TABLE IF NOT EXISTS my_table_counter (
  mykey text,
  count counter, 
  PRIMARY KEY (mykey)
);

然后对于每次插入到表中，执行计数器更新：

Then for every insert into your table, do counter update:

INSERT into my_table (mykey, mydata) VALUES (?, ?);
UPDATE my_table_counter SET count = count + 1 WHERE mykey = ?;

要获得计数：

SELECT count FROM my_table_counter WHERE mykey = ?

请注意，计数器不是幂等的，因此在罕见的失败情况下，过度计数。上面的代码假设你只插入一个新的键。

Note that counters are not idempotent, so in a rare event of a failure your data might be under or over-counted. Also the code above assumes that you only insert with a new key.

如果你需要一个精确的计数，Cassandra可能不是一个很好的适合。此外，如果您没有使用唯一键插入，您可能需要考虑使用轻量级事务插入（IF NOT EXISTS），并仅在应用事务时更新计数器。

If you need a precise counting, Cassandra may be not a good fit for that. Also if you are not inserting with unique keys you may need to consider using light weight transaction with insert (IF NOT EXISTS) and update a counter only if transaction was applied.

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