added count API

_opensearch/rest-api/count.md

@@ -0,0 +1,103 @@
+---
+layout: default
+title: Count
+parent: REST API reference
+nav_order: 150
+---
+
+# Count
+Introduced 1.0
+{: .label .label-purple }
+
+The count API gives you quick access to the number of documents that match a query.
+You can also the use the count API to see the total number of documents in an index, a data stream, or an entire cluster.
+
+
+## Example
+
+To see the number of documents that match a query:
+
+```json
+GET opensearch_dashboards_sample_data_logs/_count
+{
+  "query": {
+    "term": {
+      "response": "200"
+    }
+  }
+}
+```
+
+You can also use the search API for the same result:
+
+```json
+GET opensearch_dashboards_sample_data_logs/_search
+{
+  "query": {
+    "term": {
+      "response": "200"
+    }
+  },
+  "size": 0,
+  "track_total_hits": true
+}
+```
+
+To see the number of documents in an index:
+
+```json
+GET opensearch_dashboards_sample_data_logs/_count
+```
+
+To check for the number of documents in a [data stream]({{site.url}}{{site.baseurl}}/opensearch/data-streams/), replace the index name with the data stream name.
+
+To see the number of documents in your cluster:
+
+```json
+GET _count
+```
+
+Alternatively, you could use the [cat indices]({{site.url}}{{site.baseurl}}/opensearch/rest-api/cat/cat-indices/) and [cat count]({{site.url}}{{site.baseurl}}/opensearch/rest-api/cat/cat-count/) APIs to see the number of documents per index or data stream.
+{: .note }
+
+
+## Path and HTTP methods
+
+```
+GET <target>/_count/<id>
+POST <target>/_count/<id>
+```
+
+
+## URL parameters
+
+All count parameters are optional.
+
+Parameter | Type | Description
+:--- | :--- | :---
+`allow_no_indices` | Boolean | If false, the request returns an error if any wildcard expression or index alias targets any closed or missing indices. Default is false.
+`analyzer` | String | The analyzer to use in the query string.
+`analyze_wildcard` | Boolean | Specifies whether to analyze wildcard and prefix queries. Default is false.
+`default_operator` | String | Indicates whether the default operator for a string query should be AND or OR. Default is OR.
+`df` | String | The default field in case a field prefix is not provided in the query string.
+`expand_wildcards` | String | Specifies the type of index that wildcard expressions can match. Supports comma-separated values. Valid values are `all` (match any index), `open` (match open, non-hidden indices), `closed` (match closed, non-hidden indices), `hidden` (match hidden indices), and `none` (deny wildcard expressions). Default is `open`.
+`ignore_unavailable` | Boolean | Specifies whether to include missing or closed indices in the response. Default is false.
+`lenient` | Boolean | Specifies whether OpenSearch should accept requests if queries have format errors (for example, querying a text field for an integer). Default is false.
+`min_score` | Float |	Include only documents with a minimum `_score` value in the result.
+`routing` | String | Value used to route the operation to a specific shard.
+`preference` | String | Specifies which shard or node OpenSearch should perform the count operation on.
+`terminate_after` | Integer | The maximum number of documents OpenSearch should process before terminating the request.
+
+## Response
+
+```json
+{
+  "count" : 14074,
+  "_shards" : {
+    "total" : 1,
+    "successful" : 1,
+    "skipped" : 0,
+    "failed" : 0
+  }
+}
+```