diff --git a/docs/reference/modules/indices/request_cache.asciidoc b/docs/reference/modules/indices/request_cache.asciidoc index fc04c5e9c63f6..8d4dc5cbc63d2 100644 --- a/docs/reference/modules/indices/request_cache.asciidoc +++ b/docs/reference/modules/indices/request_cache.asciidoc @@ -1,44 +1,30 @@ [[shard-request-cache]] -=== Shard request cache +=== 分片请求缓存Shard request cache -When a search request is run against an index or against many indices, each -involved shard executes the search locally and returns its local results to -the _coordinating node_, which combines these shard-level results into a -``global'' result set. +当对一个索引或多个索引运行搜索请求时，每个相关的分片在本地执行搜索并将其本地结果返回到 _协调_ 节点，协调节点将这些分片级别的结果组合成 ``全局`` 结果集。 -The shard-level request cache module caches the local results on each shard. -This allows frequently used (and potentially heavy) search requests to return -results almost instantly. The requests cache is a very good fit for the logging -use case, where only the most recent index is being actively updated -- -results from older indices will be served directly from the cache. +分片级别请求缓存模块缓存每个分片上的本地结果。这使得频繁使用的（可能很重的）搜索请求可立即返回结果。请求缓存非常适合日志记录用例，其中只有最新的索引处于活跃的更新状态--旧索引的结果将直接从缓存中提供。 [IMPORTANT] =================================== -By default, the requests cache will only cache the results of search requests -where `size=0`, so it will not cache `hits`, -but it will cache `hits.total`, <>, and -<>. +默认情况下，请求缓存将只缓存 `size=0` 的搜索请求的结果，因此不会缓存 `hits`，但它将缓存 `hits.total`，<>，以及<>。 + +大多数使用 `now`（请参见 <>）的查询都无法缓存。 -Most queries that use `now` (see <>) cannot be cached. =================================== [float] -==== Cache invalidation +==== 缓存失效Cache invalidation -The cache is smart -- it keeps the same _near real-time_ promise as uncached -search. +缓存是智能的——同为缓存的搜索一样，它保持近实时的承诺。 -Cached results are invalidated automatically whenever the shard refreshes, but -only if the data in the shard has actually changed. In other words, you will -always get the same results from the cache as you would for an uncached search -request. +缓存结果在分片刷新时自动失效，但只在分片中的数据实际发生更改时。换句话说，你会 +始终从缓存中获取与未缓存的搜索请求相同的结果。 -The longer the refresh interval, the longer that cached entries will remain -valid. If the cache is full, the least recently used cache keys will be -evicted. +刷新间隔越长，缓存项将保留的有效时间越长。如果缓存已满，则最近使用的缓存键将为被驱逐。 -The cache can be expired manually with the <>: +可以使用<> 手动过期缓存： [source,js] ------------------------ @@ -48,10 +34,9 @@ POST /kimchy,elasticsearch/_cache/clear?request=true // TEST[s/^/PUT kimchy\nPUT elasticsearch\n/] [float] -==== Enabling and disabling caching +==== 启用和禁用缓存 -The cache is enabled by default, but can be disabled when creating a new -index as follows: +默认是启用缓存的，但创建新索引时可以禁用，如下所示： [source,js] ----------------------------- @@ -64,8 +49,7 @@ PUT /my_index ----------------------------- // CONSOLE -It can also be enabled or disabled dynamically on an existing index with the -<> API: +也可以使用<> API 在一个已经存在的索引上动态地启用或禁用： [source,js] ----------------------------- @@ -77,10 +61,9 @@ PUT /my_index/_settings [float] -==== Enabling and disabling caching per request +==== 每个请求启用和禁用缓存 -The `request_cache` query-string parameter can be used to enable or disable -caching on a *per-request* basis. If set, it overrides the index-level setting: +查询字符串参数中的 `request_cache` 可用来在 *每个请求* 的基础上启用或禁用缓存。若设置的话，它会覆盖索引级别的设置： [source,js] ----------------------------- @@ -99,46 +82,37 @@ GET /my_index/_search?request_cache=true // CONSOLE // TEST[continued] -IMPORTANT: If your query uses a script whose result is not deterministic (e.g. -it uses a random function or references the current time) you should set the -`request_cache` flag to `false` to disable caching for that request. +IMPORTANT: 若查询使用了一个脚本，脚本结果不是确定性的（例如，使用了随机函数或引用了当前时间），就该把 `request_cache` 参数设置为 `false` 来对该请求禁用缓存。 -Requests where `size` is greater than 0 will not be cached even if the request cache is -enabled in the index settings. To cache these requests you will need to use the -query-string parameter detailed here. +`size` 大于 0 的请求不会缓存，即便在索引设置中启用了请求缓存。要缓存这些请求，需要使用此处说明的查询字符串参数。 [float] -==== Cache key +==== 缓存键 +把整个 JSON 体用作缓存键。这意味着如果 JSON 改变 -- 比如键用不同的顺序输出 -- 那么缓存键就无法被识别。 The whole JSON body is used as the cache key. This means that if the JSON changes -- for instance if keys are output in a different order -- then the cache key will not be recognised. -TIP: Most JSON libraries support a _canonical_ mode which ensures that JSON -keys are always emitted in the same order. This canonical mode can be used in -the application to ensure that a request is always serialized in the same way. +TIP: 多数 JSON 库都支持一个 _规范_ 模式，以确保 JSON 键总是以相同的顺序发出。此规范模式可用于应用程序，以确保请求始终以相同的方式序列化。 [float] -==== Cache settings +==== 缓存设置 -The cache is managed at the node level, and has a default maximum size of `1%` -of the heap. This can be changed in the `config/elasticsearch.yml` file with: +缓存是在节点级别进行管理的，并且有一个默认的最大值为堆的 `1%`。可在 `config/elasticsearch.yml` 中使用以下设置来改变： [source,yaml] -------------------------------- indices.requests.cache.size: 2% -------------------------------- -Also, you can use the +indices.requests.cache.expire+ setting to specify a TTL -for cached results, but there should be no reason to do so. Remember that -stale results are automatically invalidated when the index is refreshed. This -setting is provided for completeness' sake only. +并且，也可以使用 +indices.requests.cache.expire+ 设置来指定缓存结果的 TTL，但应该没必要这么做。 +记住，陈旧的结果在索引刷新的时候会自动失效。该设置仅是出于完整性而提供的。 [float] -==== Monitoring cache usage +==== 监控缓存使用 -The size of the cache (in bytes) and the number of evictions can be viewed -by index, with the <> API: +利用<> API，可查看索引的缓存大小（字节）和驱逐的数量： [source,js] ------------------------ @@ -146,7 +120,7 @@ GET /_stats/request_cache?human ------------------------ // CONSOLE -or by node with the <> API: +或使用<> API 来看节点的： [source,js] ------------------------