[DOCS] Reformat force merge API docs (#46685)

docs/reference/indices/forcemerge.asciidoc

@@ -1,7 +1,30 @@
 [[indices-forcemerge]]
-=== Force Merge
+=== Force merge API
+++++
+<titleabbrev>Force merge</titleabbrev>
+++++
 
-The force merge API allows you to force a <<index-modules-merge,merge>> on the
+Forces a <<index-modules-merge,merge>> on the shards of one or more indices.
+
+[source,console]
+----
+POST /twitter/_forcemerge
+----
+// TEST[setup:twitter]
+
+
+[[forcemerge-api-request]]
+==== {api-request-title}
+
+`POST /<index>/_forcemerge`
+
+`POST /_forcemerge`
+
+
+[[forcemerge-api-desc]]
+==== {api-description-title}
+
+Use the force merge API to force a <<index-modules-merge,merge>> on the
 shards of one or more indices. Merging reduces the number of segments in each
 shard by merging some of them together, and also frees up the space used by
 deleted documents. Merging normally happens automatically, but sometimes it is
@@ -15,74 +38,135 @@ mostly consist of deleted documents. This can cause very large segments to
 remain in the index which can result in increased disk usage and worse search
 performance.
 
+
+[[forcemerge-blocks]]
+===== Blocks during a force merge
+
 Calls to this API block until the merge is complete. If the client connection
 is lost before completion then the force merge process will continue in the
 background. Any new requests to force merge the same indices will also block
 until the ongoing force merge is complete.
 
-[source,console]
---------------------------------------------------
-POST /twitter/_forcemerge
---------------------------------------------------
-// TEST[setup:twitter]
 
-Force-merging can be useful with time-based indices and when using
-<<indices-rollover-index,rollover>>. In these cases each index only receives
-indexing traffic for a certain period of time, and once an index will receive
-no more writes its shards can be force-merged down to a single segment:
+[[forcemerge-multi-index]]
+===== Force merging multiple indices
 
-[source,console]
---------------------------------------------------
-POST /logs-000001/_forcemerge?max_num_segments=1
---------------------------------------------------
-// TEST[setup:twitter]
-// TEST[s/logs-000001/twitter/]
+The force merge API can be applied to more than one index with a single call, or
+even on `_all` the indices. Multi index operations are executed one shard at a
+time per node. Force merge makes the storage for the shard being merged
+temporarily increase, up to double its size in case `max_num_segments` parameter
+is set to `1`, as all segments need to be rewritten into a new one.
 
-This can be a good idea because single-segment shards can sometimes use simpler
-and more efficient data structures to perform searches.
 
-[float]
-[[forcemerge-parameters]]
-==== Request Parameters
+[[forcemerge-api-path-params]]
+==== {api-path-parms-title}
 
-The force merge API accepts the following request parameters:
+include::{docdir}/rest-api/common-parms.asciidoc[tag=index]
++
+To force merge all indices in the cluster,
+omit this parameter
+or use a value of `_all` or `*`.
 
-[horizontal]
-`max_num_segments`:: The number of segments to merge to. To fully
-merge the index, set it to `1`. Defaults to simply checking if a
-merge needs to execute, and if so, executes it.
 
-`only_expunge_deletes`:: Should the merge process only expunge segments with
-deletes in it. In Lucene, a document is not deleted from a segment, just marked
-as deleted. During a merge process of segments, a new segment is created that
-does not have those deletes. This flag allows to only merge segments that have
-deletes. Defaults to `false`.  Note that this won't override the
-`index.merge.policy.expunge_deletes_allowed` threshold.
+[[forcemerge-api-query-params]]
+==== {api-query-parms-title}
 
-`flush`::  Should a flush be performed after the forced merge. Defaults to
-`true`.
+include::{docdir}/rest-api/common-parms.asciidoc[tag=allow-no-indices]
 
-[source,console]
---------------------------------------------------
-POST /kimchy/_forcemerge?only_expunge_deletes=false&max_num_segments=100&flush=true
---------------------------------------------------
-// TEST[s/^/PUT kimchy\n/]
+include::{docdir}/rest-api/common-parms.asciidoc[tag=expand-wildcards]
++
+Defaults to `open`.
 
-[float]
-[[forcemerge-multi-index]]
-==== Multi Index
+`flush`::
+(Optional, boolean)
+If `true`,
+{es} performs a <<indices-flush,flush>> on the indices
+after the force merge.
+Defaults to `true`.
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=index-ignore-unavailable]
+
+`max_num_segments`::
++
+--
+(Optional, integer)
+The number of segments to merge to.
+To fully merge the index,
+set it to `1`.
+
+Defaults to checking if a merge needs to execute.
+If so, executes it.
+--
+
+`only_expunge_deletes`::
++
+--
+(Optional, boolean)
+If `true`,
+only expunge segments containing document deletions.
+Defaults to `false`.
+
+In Lucene,
+a document is not deleted from a segment;
+just marked as deleted.
+During a merge,
+a new segment is created
+that does not contain those document deletions.
+
+NOTE: This parameter does *not* override the
+`index.merge.policy.expunge_deletes_allowed` setting.
+--
 
-The force merge API can be applied to more than one index with a single call, or
-even on `_all` the indices. Multi index operations are executed one shard at a
-time per node. Force merge makes the storage for the shard being merged
-temporarily increase, up to double its size in case `max_num_segments` is set
-to `1`, as all segments need to be rewritten into a new one.
 
+[[forcemerge-api-example]]
+==== {api-examples-title}
+
+
+[[forcemerge-api-specific-ex]]
+===== Force merge a specific index
 
 [source,console]
---------------------------------------------------
+----
+POST /twitter/_forcemerge
+----
+// TEST[continued]
+
+
+[[forcemerge-api-multiple-ex]]
+===== Force merge several indices
+
+[source,console]
+----
 POST /kimchy,elasticsearch/_forcemerge
+----
+// TEST[s/^/PUT kimchy\nPUT elasticsearch\n/]
+
+
+[[forcemerge-api-all-ex]]
+===== Force merge all indices
 
+[source,console]
+----
 POST /_forcemerge
+----
+
+
+[[forcemerge-api-time-based-index-ex]]
+===== Time-based indices
+
+Force-merging is useful for time-based indices,
+particularly when using <<indices-rollover-index,rollover>>.
+In these cases,
+each index only receives indexing traffic for a certain period of time.
+Once an index receive no more writes,
+its shards can be force-merged to a single segment.
+
+[source,console]
 --------------------------------------------------
-// TEST[s/^/PUT kimchy\nPUT elasticsearch\n/]
+POST /logs-000001/_forcemerge?max_num_segments=1
+--------------------------------------------------
+// TEST[setup:twitter]
+// TEST[s/logs-000001/twitter/]
+
+This can be a good idea because single-segment shards can sometimes use simpler
+and more efficient data structures to perform searches.