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[DOCS] Update the docs about the fact that global ordinals for _parent field are loaded eagerly instead of lazily by default. 

Relates to #8053
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Martijn van Groningen 2017-03-22 10:31:16 +01:00
parent 25448e3046
commit b116b8f0cb
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1 changed files with 12 additions and 6 deletions
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18
docs/reference/mapping/fields/parent-field.asciidoc
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@ -121,11 +121,17 @@ Global ordinals need to be rebuilt after any change to a shard. The more
parent id values are stored in a shard, the longer it takes to rebuild the
global ordinals for the `_parent` field.
Global ordinals, by default, are built lazily: the first parent-child query or
aggregation after a refresh will trigger building of global ordinals. This can
introduce a significant latency spike for your users. You can use
<<global-ordinals,eager_global_ordinals>> to shift the cost of building global
ordinals from query time to refresh time, by mapping the `_parent` field as follows:
Global ordinals, by default, are built eagerly: if the index has changed,
global ordinals for the `_parent` field will be rebuilt as part of the refresh.
This can add significant time the refresh. However most of the times this is the
right trade-off, otherwise global ordinals are rebuilt when the first parent-child
query or aggregation is used. This can introduce a significant latency spike for
your users and usually this is worse as multiple global ordinals for the `_parent`
field may be attempt rebuilt within a single refresh interval when many writes
are occurring.
When the parent/child is used infrequently and writes occur frequently it may
make sense to disable eager loading:
[source,js]
--------------------------------------------------
@ -136,7 +142,7 @@ PUT my_index
"my_child": {
"_parent": {
"type": "my_parent",
"eager_global_ordinals": true
"eager_global_ordinals": false
}
}
}