原文地址: https://www.elastic.co/guide/en/elasticsearch/reference/7.7/docs-refresh.html, 原文档版权归 www.elastic.co 所有
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Elasticsearch Guide [7.7] » REST APIs » Document APIs » ?refresh
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?refreshedit

The Index, Update, Delete, and Bulk APIs support setting refresh to control when changes made by this request are made visible to search. These are the allowed values:

Empty string or true
Refresh the relevant primary and replica shards (not the whole index) immediately after the operation occurs, so that the updated document appears in search results immediately. This should ONLY be done after careful thought and verification that it does not lead to poor performance, both from an indexing and a search standpoint.
wait_for
Wait for the changes made by the request to be made visible by a refresh before replying. This doesn’t force an immediate refresh, rather, it waits for a refresh to happen. Elasticsearch automatically refreshes shards that have changed every index.refresh_interval which defaults to one second. That setting is dynamic. Calling the Refresh API or setting refresh to true on any of the APIs that support it will also cause a refresh, in turn causing already running requests with refresh=wait_for to return.
false (the default)
Take no refresh related actions. The changes made by this request will be made visible at some point after the request returns.

Choosing which setting to useedit

Unless you have a good reason to wait for the change to become visible, always use refresh=false (the default setting). The simplest and fastest choice is to omit the refresh parameter from the URL.

If you absolutely must have the changes made by a request visible synchronously with the request, you must choose between putting more load on Elasticsearch (true) and waiting longer for the response (wait_for). Here are a few points that should inform that decision:

  • The more changes being made to the index the more work wait_for saves compared to true. In the case that the index is only changed once every index.refresh_interval then it saves no work.
  • true creates less efficient indexes constructs (tiny segments) that must later be merged into more efficient index constructs (larger segments). Meaning that the cost of true is paid at index time to create the tiny segment, at search time to search the tiny segment, and at merge time to make the larger segments.
  • Never start multiple refresh=wait_for requests in a row. Instead batch them into a single bulk request with refresh=wait_for and Elasticsearch will start them all in parallel and return only when they have all finished.
  • If the refresh interval is set to -1, disabling the automatic refreshes, then requests with refresh=wait_for will wait indefinitely until some action causes a refresh. Conversely, setting index.refresh_interval to something shorter than the default like 200ms will make refresh=wait_for come back faster, but it’ll still generate inefficient segments.
  • refresh=wait_for only affects the request that it is on, but, by forcing a refresh immediately, refresh=true will affect other ongoing request. In general, if you have a running system you don’t wish to disturb then refresh=wait_for is a smaller modification.

refresh=wait_for Can Force a Refreshedit

If a refresh=wait_for request comes in when there are already index.max_refresh_listeners (defaults to 1000) requests waiting for a refresh on that shard then that request will behave just as though it had refresh set to true instead: it will force a refresh. This keeps the promise that when a refresh=wait_for request returns that its changes are visible for search while preventing unchecked resource usage for blocked requests. If a request forced a refresh because it ran out of listener slots then its response will contain "forced_refresh": true.

Bulk requests only take up one slot on each shard that they touch no matter how many times they modify the shard.

Examplesedit

These will create a document and immediately refresh the index so it is visible:

PUT /test/_doc/1?refresh
{"test": "test"}
PUT /test/_doc/2?refresh=true
{"test": "test"}

These will create a document without doing anything to make it visible for search:

PUT /test/_doc/3
{"test": "test"}
PUT /test/_doc/4?refresh=false
{"test": "test"}

This will create a document and wait for it to become visible for search:

PUT /test/_doc/4?refresh=wait_for
{"test": "test"}
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