Cassandra 数据库 一致性级别 Consistency Level 设置语法

Cassandra 数据库阿木 发布于 10 天前 2 次阅读

摘要：

Cassandra 是一个分布式数据库系统，以其高可用性和可扩展性而闻名。在 Cassandra 中，一致性级别（Consistency Level）是一个关键的概念，它决定了系统在读取和写入数据时的数据一致性保证。本文将深入探讨 Cassandra 的一致性级别设置语法，包括其重要性、不同级别的使用场景以及如何在实际应用中配置。

一、

Cassandra 的设计哲学是“最终一致性”，这意味着系统在写入数据后，可能会经历一个短暂的不一致状态，但最终会达到一致性。一致性级别（Consistency Level）是控制这种最终一致性的一个重要工具。本文将围绕一致性级别设置语法展开，帮助读者更好地理解和使用 Cassandra。

二、一致性级别的重要性

1. 数据一致性保证：一致性级别决定了系统在读取和写入数据时的数据一致性保证。

2. 性能与一致性的权衡：不同的一致性级别会影响系统的性能，因此在设计系统时需要权衡性能和一致性。

3. 避免数据丢失：正确设置一致性级别可以减少数据丢失的风险。

三、Cassandra 的一致性级别设置语法

Cassandra 的一致性级别设置语法主要涉及以下两个方面：

1. 读取一致性级别

2. 写入一致性级别

1. 读取一致性级别

Cassandra 支持以下读取一致性级别：

- ONE: 只读取到第一个副本的数据，性能最高，但可能读取到过期的数据。

- SINGLE: 读取到所有副本中的第一个响应的数据，比 ONE 稍微可靠。

- QUORUM: 读取到超过一半副本的数据，是最常用的读取一致性级别。

- ALL: 读取到所有副本的数据，最可靠，但性能最低。

- ANY: 读取到任意一个副本的数据，性能最高，但可能读取到过期的数据。

示例代码：

java
// 设置读取一致性级别为 QUORUM

ReadConsistencyLevel readLevel = ReadConsistencyLevel.QUORUM;

2. 写入一致性级别

Cassandra 支持以下写入一致性级别：

- ONE: 写入到第一个副本，性能最高，但可能丢失数据。

- SINGLE: 写入到所有副本中的第一个响应的副本，比 ONE 稍微可靠。

- QUORUM: 写入到超过一半副本，是最常用的写入一致性级别。

- ALL: 写入到所有副本，最可靠，但性能最低。

- ANY: 写入到任意一个副本，性能最高，但可能丢失数据。

示例代码：

java
// 设置写入一致性级别为 ALL

WriteConsistencyLevel writeLevel = WriteConsistencyLevel.ALL;

四、一致性级别在应用中的配置

在实际应用中，可以通过以下方式配置一致性级别：

1. 在创建表时指定一致性级别

```sql

CREATE TABLE my_table (

key text PRIMARY KEY,

value text

) WITH CLUSTERING ORDER BY (key ASC)

AND read_repair_chance = 0.1

AND dclocal_read_repair_chance = 0.1

AND gc_grace_seconds = 864000

AND bloom_filter_fp_chance = 0.01

AND crc_check_chance = 1.0

AND max_index_interval = 2048

AND memtable_flush_period_in_ms = 0

AND memtable_flush_cache_size_in_mb = 64

AND memtable_compaction_threshold = 1.0

AND memtable_sstable_size_in_mb = 64

AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy'}

AND compression = {'sstable_compression': 'SnappyCompressor'}

AND default_time_to_live = 0

AND comment = '';

AND min_compaction_threshold = 1.0

AND max_compaction_threshold = 3.0

AND max_data_age_in_ms = 0

AND max_index_interval = 2048

AND read_repair_chance = 0.1

AND speculative_retry = '99.0%%'

AND dclocal_read_repair_chance = 0.1

AND speculative_retry = '99.0%%'

AND speculative_retry = '99.0%%'

AND speculative_retry = '99.0%%'

AND speculative_retry = '99.0%%'

AND speculative_retry = '99.0%%'

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