redis缓存原理

发布网友 发布时间：2022-04-20 00:52

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懂视网 时间：2022-05-01 21:13

 发布：

import redis
pool = redis.ConnectionPool(host=‘192.168.14.35‘, port=6379,password="Alex3714" ,db=1)
r = redis.Redis(connection_pool=pool)

r.publish("fm87.7", "big SB!")

什么时候用关系型数据库，什么时候 用NoSQL?

Go for legacy relational databases (RDBMS) when:

1. The data is well structured, and lends itself to a tabular arrangement (rows and columns) in a relational database. Typical examples: bank account info, customer order info, customer info, employee info, department info etc etc.
2. Another aspect of the above point is : schema oriented data model. When you design a data model (tables, relationships etc) for a potential use of RDBMS, you need to come up with a well defined schema: there will be these many tables, each table having a known set of columns that store data in known typed format (CHAR, NUMBER, BLOB etc).
3. Very Important: Consider whether the data is transactional in nature. In other words, whether the data will be stored, accessed and updated in the context of transactions providing the ACID semantics or is it okay to compromise some/all of these properties.
4. Correctness is also important and any compromise is _unacceptable_. This stems from the fact that in most NoSQL databases, consistency is traded off in favor of performance and scalability (points on NoSQL databases are elaborated below).
5. There is no strong/compelling need for a scale out architecture ; a database that linearly scales out (horizontal scaling) to multiple nodes in a cluster.
6. The use case is not for “high speed data ingestion”.
7. If the client applications are expecting to quickly stream large amounts of data in/out of the database then relational database may not be a good choice since they are not really designed for scaling write heavy workloads.
8. In order to achieve ACID properties, lots of additional background work is done especially in writer (INSERT, UPDATE, DELETE) code paths. This definitely affects performance.
9. The use case is not for “storing enormous amounts of data in the range of petabytes”.

Go for NoSQL databases when:

1. There is no fixed (and predetermined) schema that data fits in:
2. Scalability, Performance (high throughput and low operation latency), Continuous Availability are very important requirements to be met by the underlying architecture of database.
3. Good choice for “High Speed Data Ingestion”. Such applications (for example IoT style) which generate millions of data points in a second and need a database capable of providing extreme write scalability.
4. The inherent ability to horizontally scale allows to store large amounts of data across commodity servers in the cluster. They usually use low cost resources, and are able to linearly add compute and storage power as the demand grows.

source page https://www.quora.com/When-should-you-use-NoSQL-vs-regular-RDBMS 

redis缓存数据库

标签：tle   命令   ica   存储   api   就会   cond   another   body   

热心网友 时间：2022-05-01 18:21

redis缓存原理是sql语句时key值，查询结果resultSet是value，当同一个查询语句访问时（select * from t_proct），只要曾经查询过，调用缓存直接返回resultSet，节省了数据库读取磁盘数据的时间。

redis的存储分为内存存储、磁盘存储和log文件三部分，配置文件中有三个参数对其进行配置。

save seconds updates，save配置，指出在多长时间内，有多少次更新操作，就将数据同步到数据文件。这个可以多个条件配合，比如默认配置文件中的设置，就设置了三个条件。

appendonly yes/no ，appendonly配置，指出是否在每次更新操作后进行日志记录，如果不开启，可能会在断电时导致一段时间内的数据丢失。因为redis本身同步数据文件是按上面的save条件来同步的，所以有的数据会在一段时间内只存在于内存中。

扩展资料

redis的出现，很大程度补偿了memcached这类key/value存储的不足，在部 分场合可以对关系数据库起到很好的补充作用。它提供了Java，C/C++，C#，PHP，JavaScript，Perl，Object-C，Python，Ruby，Erlang等客户端，使用很方便。 

Redis支持主从同步。数据可以从主服务器向任意数量的从服务器上同步，从服务器可以是关联其他从服务器的主服务器。这使得Redis可执行单层树复制。

存盘可以有意无意的对数据进行写操作。由于完全实现了发布/订阅机制，使得从数据库在任何地方同步树时，可订阅一个频道并接收主服务器完整的消息发布记录。同步对读取操作的可扩展性和数据冗余很有帮助。

redis的官网地址，redis.io。（域名后缀io属于国家域名，是british Indian Ocean territory，即英属印度洋领地）