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Update search-type.asciidoc 

Changed search_type docs to reflect that the `(dfs_)query_and_fetch` modes are an internal optimization and should not be specified explicitly by the user.

Relates to #9606
This commit is contained in:
Clinton Gormley 2015-03-02 10:54:52 +01:00
parent 8cba6509e4
commit c223ed0db4
1 changed files with 30 additions and 27 deletions
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docs/reference/search/request/search-type.asciidoc
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@ -34,42 +34,25 @@ to execute on a *per search request* basis. The type can be configured
by setting the *search_type* parameter in the query string. The types
are:
[[query-and-fetch]]
==== Query And Fetch
Parameter value: *query_and_fetch*.
The most naive (and possibly fastest) implementation is to simply
execute the query on all relevant shards and return the results. Each
shard returns `size` results. Since each shard already returns `size`
hits, this type actually returns `size` times `number of shards` results
back to the caller.
[[query-then-fetch]]
==== Query Then Fetch
Parameter value: *query_then_fetch*.
The query is executed against all shards, but only enough information is
returned (*not the document content*). The results are then sorted and
ranked, and based on it, *only the relevant shards* are asked for the
actual document content. The return number of hits is exactly as
specified in `size`, since they are the only ones that are fetched. This
is very handy when the index has a lot of shards (not replicas, shard id
groups).
The request is processed in two phases. In the first phase, the query
is forwarded to *all involved shards*. Each shard executes the search
and generates a sorted list of results, local to that shard. Each
shard returns *just enough information* to the coordinating node
to allow it merge and re-sort the shard level results into a globally
sorted set of results, of maximum length `size`.
During the second phase, the coordinating node requests the document
content (and highlighted snippets, if any) from *only the relevant
shards*.
NOTE: This is the default setting, if you do not specify a `search_type`
in your request.
[[dfs-query-and-fetch]]
==== Dfs, Query And Fetch
Parameter value: *dfs_query_and_fetch*.
Same as "Query And Fetch", except for an initial scatter phase which
goes and computes the distributed term frequencies for more accurate
scoring.
[[dfs-query-then-fetch]]
==== Dfs, Query Then Fetch
@ -97,3 +80,23 @@ Parameter value: *scan*.
The `scan` search type disables sorting in order to allow very efficient
scrolling through large result sets. See <<scroll-scan>> for more.
[[query-and-fetch]]
==== Query And Fetch
Parameter value: *query_and_fetch*.
The `query_and_fetch` mode is an *internal* optimization which
is chosen automatically when a `query_then_fetch` request
targets a single shard only. Both phases of `query_then_fetch`
are executed in a single pass. This mode should not be
explicitly specified by the user.
[[dfs-query-and-fetch]]
==== Dfs, Query And Fetch
Parameter value: *dfs_query_and_fetch*.
Same as `query_and_fetch`, except for an initial scatter phase which
goes and computes the distributed term frequencies for more accurate
scoring. This mode should not be explicitly specified by the user.