https://www.elastic.co/guide/en/elasticsearch/reference/7.x/release-highlights-7.0.0.html


Adaptive replica selection enabled by default

默认开启自适应副本选择


In Elasticsearch 6.x and prior, a series of search requests to the same shard 
would be forwarded to the primary and each replica in round-robin fashion. 
This could prove problematic if one node starts a long garbage collection .
search requests could still be forwarded to the slow node regardless 
and would have an impact on search latency.

7.0之前的版本 一系列同一分片的搜索请求 会以轮询方式转发给主副本和每个副本。
如果一个节点启动了长时间的垃圾收集，这可能会带来问题。

Each node tracks and compares how long search requests to other nodes take, 
and uses this information to adjust how frequently to send requests to shards on particular nodes. 


This option was disabled by default throughout 6.x, 
but we’ve heard feedback from our users that have found the setting to be very beneficial, 
so we’ve turned it on by default starting in Elasticsearch 7.0.0.

Skip shard refreshes if a shard is "search idle"


automatically in the background, by default every second. 
This provides the “near real-time” search capabilities
results are available for search requests within one second after they’d been added

A shard now transitions to being search idle after it hasn’t had any searches for thirty seconds
分片在30秒内没有任何搜索之后，转换为搜索空闲
Once a shard is search idle, all scheduled refreshes will be skipped until a search comes through,
which will trigger the next scheduled refresh. 
一旦分片搜索空闲，所有预定的刷新将被跳过，直到搜索到来，这将触发下一次计划刷新。
The new behavior is only applied if there is no explicit refresh interval set
只有在没有显示设置刷新间隔时才生效


Default to one shard
默认为一个分片
之前默认为5个分片

Of course, if you have another preferred primary shard count, you can set it via the index settings.



Lucene 8

Elasticsearch 7.0 bundles Lucene 8, which is the latest version of Lucene.

improved search performance for top-k queries 
and better ways to combine relevance signals for your searches while still maintaining speed.


Introduce the ability to minimize round-trips in cross-cluster search



New cluster coordination implementation

easy to scale and resilient to catastrophic failures. 
易于扩展和对灾难性故障的恢复能力

a pluggable cluster coordination system, with the default implementation known as Zen Discovery. 

Zen Discovery was meant to be effortless, and give our users peace of mind (as the name implies). 

禅宗发现的本意是毫不费力的，给用户带来内心的平静(顾名思义)。


Zen’s minimum_master_nodes setting was often misconfigured, 
which put clusters at a greater risk of split brains and losing data. 
Maintaining this setting across large and dynamically resizing clusters was also difficult.

minimum_master_nodes设置经常被错误配置，这会使集群面临更大的分裂大脑和丢失数据的风险。跨大型动态调整大小的集群维护此设置也很困难。

The new implementation gives safe sub-second master election times

With the minimum_master_nodes setting removed, 
growing and shrinking clusters becomes safer and easier, 
and leaves much less room to misconfigure the system. 

删除minimum_master_nodes设置后，集群的增长和收缩将变得更安全、更容易，大大减少了错误配置系统的空间。


Better support for small heaps (the real-memory circuit breaker)
更好地支持小堆(内存断路器)
adds an all-new circuit breaker that keeps track of the total memory used by the JVM 
and will reject requests if they would cause the reserved plus actual heap usage to exceed 95%. 
 
changing the default maximum buckets to return as part of an aggregation 
(search.max_buckets) to 10,000, which is unbounded by default in 6.x and prior. 

默认最大桶更改为10,000，作为聚合(search.max_buckets)的一部分返回

keep cluster alive even in the face of adversarial or novice users running large queries and aggregations.

保持集群活力
敌对用户或新手用户运行大型查询和聚合


Cross-cluster replication is production-ready


Index lifecycle management is production-ready

hot, warm, cold, and deletion phases

ILM can now manage frozen indices. 
Frozen indices are valuable for long term data storage in Elasticsearch, 
and require a smaller amount of memory (heap) in relation to the amount of data managed by a node. 

冻结的索引， 长时间保留数据


SQL is production-ready

JDBC and ODBC drivers 
There are four methods to access Elasticsearch SQL: 
through the REST endpoints, the SQL command line interface, the JDBC driver, and the ODBC driver.

High-level REST client is feature-complete


Support nanosecond timestamps


With JDK 8, an official Java time API has been introduced which can also handle nanosecond precision timestamps 

date_nanos field mapper. 

Note that aggregations are still on a millisecond resolution with this field to avoid having an explosion of buckets.

使用此字段聚合仍然以毫秒的分辨率进行，以避免桶爆炸。


Faster retrieval of top hits

users typically just look at the first page of results on your site 
and don’t care about exactly how many documents matched, 

show them “more than 10,000 hits” and then provide them with paginated results.

 
It’s quite common to have users enter frequently-occurring terms like “the” and “a” in their queries, 
which has historically forced Elasticsearch to score a lot of documents 
even when those frequent terms couldn’t possibly add much to the score.

Support for TLS 1.3


Bundle JDK in Elasticsearch distribution


Rank features

JSON logging

Script score query (aka function score 2.0)edit