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ElasticSearch节点可用的CPU核的数量，通常可以交给ElasticSearch来自行检测和判定，另外可以在``elasticsearch.yml`中显式指定。样例如下：
node.processors: 2
如下表格中的processors即CPU核的数量。
线程池的列表
| 线程池名称 | 类型 | 线程数量 | 队列长度 | 用途 |
|---|---|---|---|---|
| generic | scaling | 一般用途。 | ||
| search | fixed | (processors * 3) / 2 + 1 | 1000 | count/search |
| search_worker | fixed | (processors * 3) / 2 + 1 | unbounded | count/search |
| search_throttled | fixed | 1 | 100 | count/search/suggest/get |
| search_coordination | fixed | processors / 2 | 1000 | search-related |
| get | fixed | (processors * 3) / 2 + 1 | 1000 | get |
| analyze | fixed | 1 | 16 | analyze |
| write | fixed | processors | 10000 | index/delete/update, ingest processors, and bulk requests |
| snapshot | scaling | min(5, (processors) / 2) | snapshot/restore | |
| snapshot_meta | scaling | min(50, (processors* 3)) | snapshot repository metadata read | |
| warmer | scaling | min(5, processors / 2) | segment warm-up | |
| refresh | scaling | min(10, processors / 2) | refresh | |
| fetch_shard_started | scaling | 2 * processors | listing shard states | |
| fetch_shard_store | scaling | 2 * processors | listing shard stores | |
| flush | scaling | min(5, processors / 2) | flush/translog | |
| force_merge | fixed | max(1, processors / 8) | unbounded | force merge |
| management | scaling | 5 | cluster management | |
| system_read | fixed | min(5, processors / 2) | read | |
| system_write | fixed | min(5, processors / 2) | write | |
| system_critical_read | fixed | min(5, processors / 2) | read | |
| system_critical_write | fixed | min(5, processors / 2) | write | |
| watcher | fixed | min(5 * processors, 50) | 1000 | watch executions |
依据上述表格中的线程数量的规则，通过指定node.processors，可以推断出ElasticSearch各线程池中线程的数量。
线程池的类型
fixed
线程池中的线程数量固定，同时使用队列来缓存当前暂时无法处理的请求。
通过参数size指定线程池中线程的数量。
通过参数queue_size指定请求队列的长度，默认值为-1，表示unbounded，即为无界队列。
配置样例，如下：
thread_pool:write:size: 30queue_size: 1000
scaling
线程池中的线程数量依据一定的规则动态调整。
通过参数core、max，以及工作负载情况来判定线程的生命周期和数量。
通过参数keep_alive来决定空载情况下，线程的存活时长。
配置样例，如下：
thread_pool:warmer:core: 1max: 8keep_alive: 2m
相关资料
- Thread pools
- Watcher
- Flush API
- Translog
- Force merge API