Truncate(dev-guide): Added steps for truncate

development-guide.md

@@ -101,9 +101,14 @@ This operation should fail if it is asked to create a table that already exists.
 #### DescribeTable
 This operation should report all columns in the destination table, including Fivetran system columns such as `_fivetran_synced` and `_fivetran_deleted`. It should also provide other additional information as applicable such as data type, `primary_key` and `DecimalParams`.
 
-#### Truncate
+#### TruncateRequest
 - This operation might be requested for a table that does not exist in the destination. In that case, it should NOT fail, simply ignore the request and return `success = true`.
-- `utc_delete_before` has millisecond precision.
+- It contains an optional `SoftTruncate` field which either contains a string column `deleted_column` or boolean `history_mode`. If `deleted_column` is present, then current sync mode is `soft-delete-mode` and if `history_mode` is true then current sync mode is `history-mode`, otherwise the current sync mode is `live-mode`.
+- It contains `utc_delete_before` timestamp field which has millisecond precision and use it to DELETE/UPDATE the rows in destination table as per the sync mode:
+  - **Soft-Delete Mode:** Set `deleted_column` to TRUE where `_fivetran_synced` column value is less than `utc_delete_before`.
+  - **History Mode:** Set `_fivetran_active` column value to FALSE, `_fivetran_end` column value to `utc_delete_before` value, where `_fivetran_synced` column value is less than `utc_delete_before` and `_fivetran_active` is TRUE.
+  - **Live Mode:** DELETE the record where `_fivetran_synced` column value is less than `utc_delete_before`
+
 
 #### WriteBatchRequest
 - `replace_files` is for `upsert` operation where the rows should be inserted if they don't exist or updated if they do. Each row will always provide values for all columns. Set the `_fivetran_synced` column in the destination with the values coming in from the csv files.