DOC-754 | Added and removed consolidation options for inverted indexes and arangosearch Views (#850)

* Added and removed consolidation options for inverted indexes and arangosearch Views

* Feedback

* Update text in two more places

* Update consolidation policy description

Author: Simran-B

site/content/arangodb/3.12/develop/http-api/indexes/inverted.md

@@ -561,12 +561,14 @@ paths:
                         upon several possible configurable formulas as defined by their types.
                         The supported types are:
 
-                        - `"tier"`: consolidate based on segment byte size and live
+                        - `"tier"`: consolidate based on segment byte size skew and live
                           document count as dictated by the customization attributes.
                       type: string
                       default: tier
                     segmentsBytesFloor:
                       description: |
+                        This option is only available up to v3.12.6:
+
                         Defines the value (in bytes) to treat all smaller segments as equal for
                         consolidation selection.
                       type: integer
@@ -578,21 +580,86 @@ paths:
                       default: 8589934592
                     segmentsMax:
                       description: |
+                        This option is only available up to v3.12.6:
+
                         The maximum number of segments that are evaluated as candidates for
                         consolidation.
                       type: integer
                       default: 200
                     segmentsMin:
                       description: |
+                        This option is only available up to v3.12.6:
+
                         The minimum number of segments that are evaluated as candidates for
                         consolidation.
                       type: integer
                       default: 50
                     minScore:
                       description: |
+                        This option is only available up to v3.12.6:
+
                         Filter out consolidation candidates with a score less than this.
                       type: integer
                       default: 0
+                    maxSkewThreshold:
+                      description: |
+                        This option is available from v3.12.7 onward:
+
+                        The skew describes how much segment files vary in file size. It is a number
+                        between `0.0` and `1.0` and is calculated by dividing the largest file size
+                        of a set of segment files by the total size. For example, the skew of a
+                        200 MiB, 300 MiB, and 500 MiB segment file is `0.5` (`500 / 1000`).
+
+                        A large `maxSkewThreshold` value allows merging large segment files with
+                        smaller ones, consolidation occurs more frequently, and there are fewer
+                        segment files on disk at all times. While this may potentially improve the
+                        read performance and use fewer file descriptors, frequent consolidations
+                        cause a higher write load and thus a higher write amplification.
+                        
+                        On the other hand, a small threshold value triggers the consolidation only
+                        when there are a large number of segment files that don't vary in size a lot.
+                        Consolidation occurs less frequently, reducing the write amplification, but
+                        it can result in a greater number of segment files on disk.
+
+                        Multiple combinations of candidate segments are checked and the one with
+                        the lowest skew value is selected for consolidation. The selection process
+                        picks the greatest number of segments that together have the lowest skew value
+                        while ensuring that the size of the new consolidated segment remains under
+                        the configured `segmentsBytesMax`.
+                      type: number
+                      minimum: 0.0
+                      maximum: 1.0
+                      default: 0.4
+                    minDeletionRatio:
+                      description: |
+                        This option is available from v3.12.7 onward:
+
+                        The `minDeletionRatio` represents the minimum required deletion ratio
+                        in one or more segments to perform a cleanup of those segments.
+                        It is a number between `0.0` and `1.0`.
+
+                        The deletion ratio is the percentage of deleted documents across one or
+                        more segment files and is calculated by dividing the number of deleted
+                        documents by the total number of documents in a segment or a group of
+                        segments. For example, if there is a segment with 1000 documents of which
+                        300 are deleted and another segment with 1000 documents of which 700 are
+                        deleted, the deletion ratio is `0.5` (50%, calculated as `1000 / 2000`).
+
+                        The `minDeletionRatio` threshold must be carefully selected. A smaller
+                        value leads to earlier cleanup of deleted documents from segments and
+                        thus reclamation of disk space but it generates a higher write load.
+                        A very large value lowers the write amplification but at the same time
+                        the system can be left with a large number of segment files with a high
+                        percentage of deleted documents that occupy disk space unnecessarily.
+
+                        During cleanup, the segment files are first arranged in decreasing
+                        order of their individual deletion ratios. Then the largest subset of
+                        segments whose collective deletion ratio is greater than or equal to
+                        `minDeletionRatio` is picked.
+                      type: integer
+                      minimum: 0.0
+                      maximum: 1.0
+                      default: 0.5
                 writebufferIdle:
                   description: |
                     Maximum number of writers (segments) cached in the pool