milvus/docs/design_docs/segcore/segment_sealed.md

# SegmentSealed
SegmentSealed has an extra interface rather than SegmentInterface:

1. `LoadIndex(loadIndexInfo)`: load the index. indexInfo contains:
    1. `FieldId`
    2. `IndexParams`: index parameters in KV structure KV
    3. `VecIndex`: vector index
2. `LoadFieldData(loadFieldDataInfo)`: load column data, could be either scalar column or vector column
    1. Note: indexes and vector data for the same column may coexist. Indexes are prioritized in the search
3. `DropIndex(fieldId)`: drop and release an existing index of a specified field
4. `DropFieldData(fieldId)`: drop and release existing data for a specified field

Search is executable as long as all the columns involved in the search are loaded.

# SegmentSealedImpl internal data definition
1. `row_count_opt_`:
   1. Fill row count when loading the first entity
   2. All the other columns loaded must match the same row count
3. `xxx_ready_bitset_` & `system_ready_count_`
   1. Used to record whether the corresponding column is loaded. Bitset corresponds to FieldOffset
   2. Query is executable if and only if all the following conditions are met:
      1. system_ready_count_ == 2， which means all the system columns' RowId/Timestamp are loaded
      2. The scalar columns involved in the query is loaded
      3. For the vector columns involved in the query, either the original data or the index is loaded
4. `scalar_indexings_`: store scalar index

   1. Use StructuredSortedIndex in Knowhere
5. `primary_key_index_`: store index for pk column
   1. Use brand new ScalarIndexBase format
   2. **Note: The functions here may overlap with scalar indexes. It is recommended to replace scalar index with ScalarIndexBase**
6. `field_datas_`: store original data
   1. `aligned_vector<char>` format guarantees `int/float` data are aligned
7. `SealedIndexingRecord vecindexs_`: store vector index
8. `row_ids_/timestamps_`: RowId/Timestamp data
9. `TimestampIndex`: Index for Timestamp column
10. `schema`: schema

# SegmentSealedImpl internal function definition
1. Most functions are the implementation of the corresponding functions of the segment interface, which will not be repeated here.
2. `update_row_count`: Used to update the row_count field.
3. `mask_with_timestamps`: Use Timestamp column to update search bitmask, used to support Time Travel function.