这是我的第 56 篇原创文章
Redis 6.0.1 于 2020 年 5 月 2 日正式发布了，如 Redis 作者 antirez 所说，这是迄今为止最“企业”化的版本，也是有史以来改动最大的一个 Redis 版本，同时也是参与开发人数最多的一个版本。
所以在使用此版本之前，建议各位开发者先进行深入的测试再考虑投产，毕竟生产坏境无小事。好了，回到本文的重点，接下来我们来重点看下 Redis 6.0.1 给我们带来了那些新功能。
Redis新功能介绍
Redis 6 的更新日志，主要包含以下五部分的内容：
Redis 6.0-RC1 版新功能介绍；
Redis 6.0-RC2 版新功能介绍；
Redis 6.0-RC3 版新功能介绍；
Redis 6.0-RC4 版新功能介绍；
Redis 6.0.0 GA 版新功能介绍。
除了以上这些版本的更新日志外，还有 6.0.1 正式版的更新日志，不过这个正式版的发布时间只比 Redis 6.0.0 GA 晚了两天，因此只修复了一些 bug，所以我们只需要看以上五个日志即可。
1.Redis 6.0-rc1 更新日志
官方更新日志如下：
Redis 6 improves Redis in a number of key areas and is one of the largest Redis releases in the history of the project, so here we'll list only the biggest features in this release:
The modules system now has a number of new APIs that allow module authors to make things otherwise not possible in the past. It is possible to store arbitrary module private data in RDB files, to hook on different server events, capture and rewrite commands executions, block clients on keys, and so forth.
The Redis active expire cycle was rewritten for much faster eviction of keys that are already expired. Now the effort is tunable.
Redis now supports SSL on all channels.
ACL support, you can define users that can run only certain commands and/or can only access only certain keys patterns.
Redis now supports a new protocol called RESP3, which returns more semantical replies: new clients using this protocol can understand just from the reply what type to return to the calling program.
There is server-side support for client-side caching of key values. This feature is still experimental and will get more changes during the next release candidates, but you can already test it and read about it here: https://redis.io/topics/client-side-caching
Redis can now optionally use threads to handle I/O, allowing to serve 2 times as much operations per second in a single instance when pipelining cannot be used.
Diskless replication is now supported even on replicas: a replica is now able, under certain conditions the user can configure, to load the RDB in the first synchronization directly from the socket to the memory.
Redis-benchmark now supports a Redis Cluster mode.
SRANDMEMBER and similar commands have a better distribution.
Redis-cli improvements.
Systemd support rewritten.
A Redis Cluster proxy was released here: https://github.com/artix75/redis-cluster-proxy
A Disque module for Redis was released here: https://github.com/antirez/disque-module
此版本新增的内容最大，如下列表所示：
众多新模块（modules）API
更好的过期循环（expire cycle）
SSL
ACLs 权限控制
RESP3 协议
客户端缓存（Client side caching）
多线程 IO（Threaded I/O）
无盘复制副本（Diskless replication on replicas）
Redis-benchmark 的集群支持和 redis-cli 优化
重写 Systemd 支持（Systemd support rewrite）
Redis 集群代理与 Redis 6 一同发布（但在不同的 repo）
Disque 模块与 Redis 6 一同发布
2.Redis 6.0-rc2 更新日志
Hi Redis users, Redis 6 is approaching and will be released 30th of April. New release candidates will be released at the end of March, then another one mid April, to finally reach the GA at the end of April.
Redis 6 RC2 brings many fixes and new things, especially in the area of client side caching. This is the list of big changes in this release. As usually you can find the full list of commits at the end:
New features and improvements:
ACL LOG: log denied commands, keys accesses and authentications.
Client side caching redesigned. Now we use keys not caching slots.
Client side caching: Broadcasting mode implemented.
Client side caching: OPTIN/OPTOUT modes implemented.
Remove RDB files used for replication in persistence-less instances (option).
Fixes (only selected ones, see commits for all the fixes):
Different fixes to streams in edge cases.
Fix duplicated CLIENT SETNAME reply because of RESP3 changes.
Fix crash due to new active expire division by zero.
Avoid sentinel changes promoted_slave to be its own replica.
Fix bug on KEYS command where pattern starts with * followed by \x00.
Threaded I/O: now the main thread is used as well to do I/O.
Many fixes to modules APIs, and more to come in the next RCs.
ld2string should fail if string contains \0 in the middle.
Make the Redis test more reliable.
Fix SPOP returning nil (see #4709). WARNING: API change.
Redis 6 RC2 带来了许多修复和新功能，尤其是客户端的缓存功能，此版本的重大更改如下列表。
ACL LOG：记录拒绝的命令，密钥访问和身份验证。
重新设计了客户端缓存。现在，我们使用密钥而不是缓存插槽。
客户端缓存：已实现广播模式。
客户端缓存：已实现 OPTIN/OPTOUT 模式。
删除用于在非持久性实例中进行复制的 RDB 文件（可选）。
修复程序（仅选定的修复程序，请参阅所有修复程序的提交）：
在边缘情况下对流的不同修复。
修正由于 RESP3 更改而导致重复的 CLIENT SETNAME 答复。
修正因新的有效到期除以零而导致的崩溃。
避免将哨兵更改提升为自己的副本。
修复了 KEYS 命令中以 * 开头，后跟 \x00 的错误。
线程 I/O：现在也使用主线程来执行 I/O。
对模块API进行了许多修复，而在下一个RC中还会有更多修复。
如果字符串中间包含 \0，则 ld2string 应该失败。
使 Redis 测试更可靠。
3.Redis 6.0-rc3 更新日志
Dear users, this is a list of the major changes in this release, please check the list of commits for detail:
Fix crash due to refactoring for SSL, for the connection code.
Precise timeouts for blocking commands. Now the timeouts have HZ resolution regardless of the number of connected clinets. New timeouts are stored in a radix tree and sorted by expire time.
Fix rare crash when resizing the event loop because of CONFIG maxclients.
Fix systemd readiness after successful partial resync.
Redis-cli ask password mode to be prompted at startup (for additional safety).
Keyspace notifications added to MIGRATE / RESTORE.
Threaded I/O bugs fixed.
Implement new ACL style AUTH in Sentinel.
Make 'requirepass' more backward compatible with Redis <= 5.
ACL: Handle default user as disabled if it's off regardless of "nopass".
Fix a potential inconsistency when upgrading an instance in Redis Cluster and restarting it. The instance will act as a replica but will actually be set as a master immediately. However the choice of what to do with already expired keys, on loading, was made from the POV of replicas.
Abort transactions after -READONLY error.
Many different fixes to module APIs.
BITFIELD_RO added to call the command on read only replicas.
PSYNC2: meaningful offset implementation. Allow the disconnected master that is still sending PINGs to replicas, to be able to successfully PSYNC incrementally to new slaves, discarding the last part of the replication backlog consisting only of PINGs.
Fix pipelined MULTI/EXEC during Lua scripts are in BUSY state.
Re-fix propagation API in modules, broken again after other changes.
这个版本主要是修复了一些 bug，如下列表所示：
修复了由于重构 SSL 而导致的连接代码崩溃。
用于阻止命令的精确超时。现在超时已达到 HZ 分辨率，无论连接的 clinet 数量如何。新超时存储在基数树中并按到期时间排序。
修复了由于 CONFIG maxclients 而调整事件循环大小时发生的罕见崩溃。
修正部分重新同步成功后的 systemd 准备情况。
Redis-cli 询问密码模式将在启动时提示（以提高安全性）。
键空间通知已添加到 MIGRATE/RESTORE。
修复了线程 I/O 错误。
在 Sentinel 中实现新的 ACL 样式 AUTH。
使 'requirepass' 与 Redis<=5 更向后兼容。
ACL：如果默认用户关闭，则将其视为禁用状态，而不管其是否为“ nopass”。
修复了在 Redis 群集中升级实例时可能出现的不一致问题
-READONLY 错误后中止事务。
对模块 API 的许多不同修复。
添加了 BITFIELD_RO 以在只读副本上调用该命令。
PSYNC2：有意义的偏移量实现。允许断开连接的主机仍在向副本发送 PING，以便能够成功 PSYNC 以增量方式传递给新的从站，从而丢弃了仅由 PING 组成的复制积压。
修正 Lua 脚本处于繁忙状态时流水线的 MULTI/EXEC。
重新修复模块中的传播 API，在其他更改后再次中断。
4.Redis 6.0-rc4 更新日志
Hi all, this the latest release candidate of Redis 6. This is likely to be very similar to what you'll see in Redis 6 GA. Please test it and report any issue :-)
Main changes in this release:
* Big INFO speedup when using a lot of of clients. * Big speedup on all the blocking commands: now blocking on the same key is O(1) instead of being O(N). * Stale replicas now allow MULTI/EXEC. * New command: LCS (Longest Common Subsequence). * Add a new configuration to make DEL like UNLINK. * RDB loading speedup. * Many bugs fixed (see the commit messages at the end of this node)
此版本主要新增的内容如下：
提高了大量客户端连接时使用 INFO 命令的查询速度。
在所有阻止命令上都大大加快了速度：现在可以阻止在同一键上是 O（1）而不是 O（N）。
陈旧的副本现在允许 MULTI/EXEC。
新命令：LCS（最长公共子序列）。
添加新配置以使 DEL 像 UNLINK。
RDB 加载加速。
修复了许多错误。
5.Redis 6.0.0 GA 更新日志
Upgrade urgency CRITICAL: many bugs fixed compared to the last release candidate. Better to upgrade if you see things affecting your environment in the changelog.
Hi all, finally we have Redis 6.0.0 GA! Enjoy this new Redis release. Most of the documentation was updated today so that you can likely find what you are looking for about the new features at redis.io. This is the list of what changed compared to the previoius release candidate:
XCLAIM AOF/replicas propagation fixed.
Client side caching: new NOLOOP option to avoid getting notified about changes performed by ourselves.
ACL GENPASS now uses HMAC-SHA256 and have an optional "bits" argument. It means you can use it as a general purpose "secure random strings" primitive!
Cluster "SLOTS" subcommand memory optimization.
The LCS command is now a subcommand of STRALGO.
Meaningful offset for replicas as well. More successful partial resynchronizations.
Optimize memory usage of deferred replies.
Faster CRC64 algorithm for faster RDB loading.
XINFO STREAM FULL, a new subcommand to get the whole stream state.
CLIENT KILL USER.
MIGRATE AUTH2 option, for ACL style authentication support.
Other random bugfixes.
此日志更新的主要内容如下：
XCLAIM AOF/replicas 传播已修复。
客户端缓存：新的 NOLOOP 选项以避免收到有关自己执行的更改。
ACL GENPASS 现在使用 HMAC-SHA256，并具有一个可选的“位”参数。这意味着您可以将其用作通用的“安全随机字符串”原始！
群集“SLOTS”子命令的内存优化。
LCS 命令现在是 STRALGO 的子命令。
副本的有意义的偏移量。更成功的部分重新同步。
优化延迟回复的内存使用。
更快的 CRC64 法可更快地加载 RDB。
XINFO STREAM FULL，一个新的子命令，用于获取整个流状态。
CLIENT KILL USER <用户名>。
MIGRATE AUTH2 选项，用于 ACL 样式身份验证支持。
修正了一些其他错误。
Redis 6.0.1 正式版的下载地址为：https://redis.io/
官方的更新日志（英文）：https://raw.githubusercontent.com/antirez/redis/6.0/00-RELEASENOTES
总结
综合以上所有版本的更新日志，我们发现这次 Redis 6.0 带来的主要功能是：
提供了众多的新模块（modules）API
提供了客户端缓存功能
多线程 I/O 能力
提升了 RDB 日志的加载速度
修改了若干个 bug 和一些优化
其中多线程 I/O 是我们最关注的功能了，有人用它和单线程的版本做了一个性能测试，如下图所示：
（注：图片来源于 iTushou.com）
从以上结果可以看到 GET/SET 命令在多线程版本中的性能相比单线程已经翻倍了。
总体来说，此次 Redis 6.0 带给我们的功能还是很多且比较实用的，只是版本改动很大，因此我们需要一定的时间和大量的测试验证之后才建议上线。
最后的话
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参考 & 鸣谢
Redis 官方文档
别再问我 new 字符串创建了几个对象了！我来证明给你看！
String性能提升10倍的几个方法！(源码+原理分析)
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