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Docs: Refine note about `after_key` (#50475) 

* Docs: Refine note about `after_key`

I was curious about composite aggregations, specifically I wanted to
know how to write a composite aggregation that had all of its buckets
filtered out so you *had* to use the `after_key`. Then I saw that we've
declared composite aggregations not to work with pipelines in #44180. So
I'm not sure you *can* do that any more. Which makes the note about
`after_key` inaccurate. This rejiggers that section of the docs a little
so it is more obvious that you send the `after_key` back to us. And so
it is more obvious that you should *only* use the `after_key` that we
give you rather than try to work it out for yourself.

* Apply suggestions from code review

Co-Authored-By: James Rodewig <james.rodewig@elastic.co>

Co-authored-by: James Rodewig <james.rodewig@elastic.co>
This commit is contained in:
Nik Everett 2020-01-02 10:02:55 -05:00
parent 7539fbb30f
commit 55107ce8ae
1 changed files with 8 additions and 12 deletions
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20
docs/reference/aggregations/bucket/composite-aggregation.asciidoc
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@ -441,7 +441,7 @@ GET /_search
... ...
"aggregations": { "aggregations": {
"my_buckets": { "my_buckets": {
"after_key": { <1> "after_key": {
"date": 1494288000000, "date": 1494288000000,
"product": "mad max" "product": "mad max"
}, },
@ -467,17 +467,9 @@ GET /_search
-------------------------------------------------- --------------------------------------------------
// TESTRESPONSE[s/\.\.\.//] // TESTRESPONSE[s/\.\.\.//]
<1> The last composite bucket returned by the query. To get the next set of buckets, resend the same aggregation with the `after`
parameter set to the `after_key` value returned in the response.
NOTE: The `after_key` is equals to the last bucket returned in the response before For example, this request uses the `after_key` value provided in the previous response:
any filtering that could be done by <<search-aggregations-pipeline, Pipeline aggregations>>.
If all buckets are filtered/removed by a pipeline aggregation, the `after_key` will contain
the last bucket before filtering.
The `after` parameter can be used to retrieve the composite buckets that are **after**
the last composite buckets returned in a previous round.
For the example below the last bucket can be found in `after_key` and the next
round of result can be retrieved with:
[source,console] [source,console]
-------------------------------------------------- --------------------------------------------------
@ -501,6 +493,10 @@ GET /_search
<1> Should restrict the aggregation to buckets that sort **after** the provided values. <1> Should restrict the aggregation to buckets that sort **after** the provided values.
NOTE: The `after_key` is *usually* the key to the last bucket returned in
the response, but that isn't guaranteed. Always use the returned `after_key` instead
of derriving it from the buckets.
==== Early termination ==== Early termination
For optimal performance the <<index-modules-index-sorting,index sort>> should be set on the index so that it matches For optimal performance the <<index-modules-index-sorting,index sort>> should be set on the index so that it matches