ES基本概念：https://developer.51cto.com/art/201904/594615.htm
反向索引又叫倒排索引，是根据文章内容中的关键字建立索引。
搜索引擎原理就是建立反向索引。
Elasticsearch 在 Lucene 的基础上进行封装，实现了分布式搜索引擎。
Elasticsearch 中的索引、类型和文档的概念比较重要，类似于 MySQL 中的数据库、表和行。
Elasticsearch 也是 Master-slave 架构，也实现了数据的分片和备份。
Elasticsearch 一个典型应用就是 ELK 日志分析系统。

ES详细解释及使用：https://blog.csdn.net/andyzhaojianhui/article/details/75195296

Elasticsearch与JDK版本对应
https://www.elastic.co/guide/en/elasticsearch/reference/index.html

IK分词器版本要求
https://github.com/medcl/elasticsearch-analysis-ik

启动Elasticsearch报错解决方案

[2020-07-08T15:45:03,438][WARN ][o.e.b.JNANatives         ] [node-1] unable to install syscall filter: 
java.lang.UnsupportedOperationException: seccomp unavailable: requires kernel 3.5+ with CONFIG_SECCOMP and CONFIG_SECCOMP_FILTER compiled in

ERROR: [3] bootstrap checks failed
[1]: max file descriptors [4096] for elasticsearch process is too low, increase to at least [65535]
[2]: max number of threads [1024] for user [daniel] is too low, increase to at least [4096]
[3]: max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144]

参考以下连接解决
https://www.cnblogs.com/socketqiang/p/11363024.html

ERROR: [1] bootstrap checks failed
[1]: max number of threads [1024] for user [daniel] is too low, increase to at least [4096]
主要是/etc/security/limits.d/90-nproc.conf 下用户线程个数限制
解决方法： 切换到root用户

# Default limit for number of user's processes to prevent
# accidental fork bombs.
# See rhbz #432903 for reasoning.*          soft    nproc     4096
root       soft    nproc     unlimited

可参考：
https://blog.csdn.net/xuexin736/article/details/80203898

未完待续