This change adds the response headers of the original search request
in the stored response in order to be able to restore them when retrieving a result
from the async-search index. It also ensures that response headers are preserved for
users that retrieve a final response on a running search task.
Partial response can eventually return response headers too but this change only ensures
that they are present when the response if final.
Relates #33936
`AsyncSearchActionTests` currently fails quite often. That is since the introduction of `RestSubmitAsyncSearchActionTests` which indirectly manipulates the channels being tracked in `RestCancellableNodeClient`. There are channels left in the map after `RestSubmitAsyncSearchActionTests` is run, and later `AsyncSearchActionTests` checks that there are no channels in the map which makes each test method fail. This is particularily hard to reproduce as the order in which tests are run appears to be platform dependent.
The test cluster assertion that there are no channels in the map only makes sense in the context of internal cluster tests, while there may be collisions with unit tests that register http channels as part of their testing.
This can be solved by renaming `AsyncSearchActionTests` to `AsyncSearchActionIT`. This way it won't be run as part of unit tests but rather within another JVM where the number of channels is `0` and such assumption holds, because there are no expected manual manipulation of the channels.
Relates to #54180
This change introduces a new API in x-pack basic that allows to track the progress of a search.
Users can submit an asynchronous search through a new endpoint called `_async_search` that
works exactly the same as the `_search` endpoint but instead of blocking and returning the final response when available, it returns a response after a provided `wait_for_completion` time.
````
GET my_index_pattern*/_async_search?wait_for_completion=100ms
{
"aggs": {
"date_histogram": {
"field": "@timestamp",
"fixed_interval": "1h"
}
}
}
````
If after 100ms the final response is not available, a `partial_response` is included in the body:
````
{
"id": "9N3J1m4BgyzUDzqgC15b",
"version": 1,
"is_running": true,
"is_partial": true,
"response": {
"_shards": {
"total": 100,
"successful": 5,
"failed": 0
},
"total_hits": {
"value": 1653433,
"relation": "eq"
},
"aggs": {
...
}
}
}
````
The partial response contains the total number of requested shards, the number of shards that successfully returned and the number of shards that failed.
It also contains the total hits as well as partial aggregations computed from the successful shards.
To continue to monitor the progress of the search users can call the get `_async_search` API like the following:
````
GET _async_search/9N3J1m4BgyzUDzqgC15b/?wait_for_completion=100ms
````
That returns a new response that can contain the same partial response than the previous call if the search didn't progress, in such case the returned `version`
should be the same. If new partial results are available, the version is incremented and the `partial_response` contains the updated progress.
Finally if the response is fully available while or after waiting for completion, the `partial_response` is replaced by a `response` section that contains the usual _search response:
````
{
"id": "9N3J1m4BgyzUDzqgC15b",
"version": 10,
"is_running": false,
"response": {
"is_partial": false,
...
}
}
````
Asynchronous search are stored in a restricted index called `.async-search` if they survive (still running) after the initial submit. Each request has a keep alive that defaults to 5 days but this value can be changed/updated any time:
`````
GET my_index_pattern*/_async_search?wait_for_completion=100ms&keep_alive=10d
`````
The default can be changed when submitting the search, the example above raises the default value for the search to `10d`.
`````
GET _async_search/9N3J1m4BgyzUDzqgC15b/?wait_for_completion=100ms&keep_alive=10d
`````
The time to live for a specific search can be extended when getting the progress/result. In the example above we extend the keep alive to 10 more days.
A background service that runs only on the node that holds the first primary shard of the `async-search` index is responsible for deleting the expired results. It runs every hour but the expiration is also checked by running queries (if they take longer than the keep_alive) and when getting a result.
Like a normal `_search`, if the http channel that is used to submit a request is closed before getting a response, the search is automatically cancelled. Note that this behavior is only for the submit API, subsequent GET requests will not cancel if they are closed.
Asynchronous search are not persistent, if the coordinator node crashes or is restarted during the search, the asynchronous search will stop. To know if the search is still running or not the response contains a field called `is_running` that indicates if the task is up or not. It is the responsibility of the user to resume an asynchronous search that didn't reach a final response by re-submitting the query. However final responses and failures are persisted in a system index that allows
to retrieve a response even if the task finishes.
````
DELETE _async_search/9N3J1m4BgyzUDzqgC15b
````
The response is also not stored if the initial submit action returns a final response. This allows to not add any overhead to queries that completes within the initial `wait_for_completion`.
The `.async-search` index is a restricted index (should be migrated to a system index in +8.0) that is accessible only through the async search APIs. These APIs also ensure that only the user that submitted the initial query can retrieve or delete the running search. Note that admins/superusers would still be able to cancel the search task through the task manager like any other tasks.
Relates #49091
Co-authored-by: Luca Cavanna <javanna@users.noreply.github.com>
Ryan Ernst
Jim Ferenczi
Luca Cavanna