Add composite aggregation documentation

_aggregations/bucket/composite.md

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+---
+layout: default
+title: Composite
+parent: Bucket aggregations
+grand_parent: Aggregations
+nav_order: 20
+has_children: true
+---
+
+# Composite
+
+The `composite` aggregation is a multi-bucket aggregation that creates composite buckets from different sources. It is useful for efficiently paginating multi-level aggregations and retrieving all buckets. Composite buckets are built from combinations of values extracted from documents for each specified source field.
+
+## Syntax
+
+```json
+{
+  "composite": {
+    "sources": [
+      {
+        "source_field_1": {
+          "terms": {
+            "field": "field_name"
+          }
+        }
+      },
+      {
+        "source_field_2": {
+          "terms": {
+            "field": "another_field_name"
+          }
+        }
+      }
+    ]
+  }
+}
+```
+{% include copy-curl.html %}
+
+Property | Description |
+---------|------------|
+`composite` | The aggregation type.
+`sources ` | An array of source objects, where each object defines a source field for the composite buckets.
+`terms` | The subaggregation type used to extract the values from the specified field for each source. 
+`field` | The field name in your documents from which the values will be extracted for the corresponding source.
+
+For example, consider the following document: 
+
+```json
+{
+  "product": "T-Shirt",
+  "category": "Clothing",
+  "brand": "Acme",
+  "price": 19.99,
+  "sizes": ["S", "M", "L"],
+  "colors": ["red", "blue"]
+}
+```
+{% include copy-curl.html %}
+
+Using `sizes` and `colors` as source fields for the aggregation results in the following composite buckets: 
+
+```json
+{ "sizes": "S", "colors": "red" }
+{ "sizes": "S", "colors": "blue" }
+{ "sizes": "M", "colors": "red" }
+{ "sizes": "M", "colors": "blue" }
+{ "sizes": "L", "colors": "red" }
+{ "sizes": "L", "colors": "blue" }
+```
+{% include copy-curl.html %}
+
+## Compatibility and limitations 
+
+<SME: What version of OpenSearch is this compatible with? What are the limitations?>
+
+## Performance considerations
+
+<What are the performance implications or best practices for using this aggregation?>

_aggregations/bucket/early-termination.md

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+---
+layout: default
+title: Early termination
+parent: Composite
+grand_parent: Bucket aggregations
+great_grand_parent: Aggregations
+nav_order: 35
+---

_aggregations/bucket/missing-bucket.md

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+---
+layout: default
+title: Missing bucket
+parent: Composite
+grand_parent: Bucket aggregations
+great_grand_parent: Aggregations
+nav_order: 20
+---

_aggregations/bucket/mixing-value-sources.md

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+---
+layout: default
+title: Mixing value sources
+parent: Composite
+grand_parent: Bucket aggregations
+great_grand_parent: Aggregations
+nav_order: 10
+---
+
+# Mixing value sources
+
+The `sources` parameter in the composite aggregation defines the source fields and aggregation types to use when building composite buckets. You can mix and match multiple value sources, such as `terms`, `histogram`, `date_histogram`, and `geotile_grid`, to create unique combinations of data aggregations.
+
+The order in which the sources are defined controls the order in which the keys are returned in the composite buckets. You must use a unique name when defining sources for the composite aggregation.
+
+---
+
+## Example: Mixing terms and histogram value sources
+
+The following example creates composite buckets that combine the `product` field (using the `terms` value source) and the `price` field (using the `histogram` value source):
+
+```json
+GET /test_index/_search
+{
+  "size": 0,
+  "aggs": {
+    "my_buckets": {
+      "composite": {
+        "sources": [
+          { "product": { "terms": { "field": "product.keyword" } } },
+          { "price_range": { "histogram": { "field": "price", "interval": 10 } } }
+        ]
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+This query defines two value sources:
+
+- `product`: This source uses the terms value source to create buckets for each unique value of the `product.keyword` field.
+- `price_range`: This source uses the `histogram` value source to create buckets based on the `price` field, grouped into intervals of `10`.
+
+The resulting composite buckets will have a structure similar to the following example:
+
+```json
+{
+  "data": [
+    {
+      "key": {
+        "product": "Jeans",
+        "price_range": 40
+      },
+      "doc_count": 1
+    },
+    {
+      "key": {
+        "product": "Sneakers",
+        "price_range": 70
+      },
+      "doc_count": 1
+    },
+    {
+      "key": {
+        "product": "T-Shirt",
+        "price_range": 10
+      },
+      "doc_count": 1
+    }
+  ]
+}
+```
+Each composite bucket will contain the product name and the corresponding price range, allowing you to analyze the distribution of products across different price ranges.
+
+---
+
+## Example: Mixing date histogram and geotile grid value source
+
+The following example combines the `date_histogram` and `geotile_grid` value sources to create composite buckets based on timestamps and geographic locations:
+
+```json
+GET /test_index/_search
+{
+  "size": 0,
+  "aggs": {
+    "my_buckets": {
+      "composite": {
+        "sources": [
+          { "date": { "date_histogram": { "field": "timestamp", "calendar_interval": "1d" } } },
+          { "location": { "geotile_grid": { "field": "location", "precision": 3 } } }
+        ]
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+This query defines two value sources:
+
+- `date`: This source uses the `date_histogram` value source to group documents based on the day of the `timestamp` field.
+- `location`: This source uses the `geotile_grid` value source to aggregate `geo_point` data into buckets that correspond to cells in a grid, with a precision of `3`.
+
+The resulting composite buckets will have a structure similar to the following example: 
+
+```json
+{
+  "took": 34,
+  "timed_out": false,
+  "_shards": {
+    "total": 1,
+    "successful": 1,
+    "skipped": 0,
+    "failed": 0
+  },
+  "hits": {
+    "total": {
+      "value": 3,
+      "relation": "eq"
+    },
+    "max_score": null,
+    "hits": []
+  },
+  "aggregations": {
+    "my_buckets": {
+      "buckets": []
+    }
+  }
+}
+```
+
+## Considerations
+
+When mixing value sources in the `composite` aggregation, keep the following point in mind: 
+
+- <SME: What are the considerations? Please list them here.>

_aggregations/bucket/ordering-composite-buckets.md

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+---
+layout: default
+title: Ordering composite buckets
+parent: Composite
+grand_parent: Bucket aggregations
+great_grand_parent: Aggregations
+nav_order: 15
+---

_aggregations/bucket/size-pagination.md

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+---
+layout: default
+title: Size and pagination
+parent: Composite
+grand_parent: Bucket aggregations
+great_grand_parent: Aggregations
+nav_order: 25
+---

_aggregations/bucket/subaggregations.md

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+---
+layout: default
+title: Subaggregations
+parent: Composite
+grand_parent: Bucket aggregations
+great_grand_parent: Aggregations
+nav_order: 30
+---