IDX.COUNTCount index entries matching a range or equality predicate.
| 语法 | IDX.COUNT name RANGE min max | EQ value |
| 分组 | index |
| 参数个数 | -4 |
| 起始版本 | 3.0.0 |
| 标志 | readonly, extension |
| 复杂度 | O(log N + matched) per shard — NOT an O(1) counter and not a B-tree rank query; it counts the matched range |
| Redis 兼容性 | kevy-only: nearest is FT.SEARCH with LIMIT 0 0 |