tidb-lightning: update wording about parallel import (#20431)

Author: lilin90

tidb-lightning/tidb-lightning-distributed-import.md

@@ -5,7 +5,7 @@ summary: Learn the concept, user scenarios, usages, and limitations of importing
 
 # Use TiDB Lightning to Import Data in Parallel
 
-Since v5.3.0, the [physical import mode](/tidb-lightning/tidb-lightning-physical-import-mode.md) of TiDB Lightning supports the parallel import of a single table or multiple tables. By simultaneously running multiple TiDB Lightning instances, you can import data in parallel from different single tables or multiple tables. In this way, TiDB Lightning provides the ability to scale horizontally, which greatly reduces the time required to import large amount of data.
+Since v5.3.0, the [physical import mode](/tidb-lightning/tidb-lightning-physical-import-mode.md) of TiDB Lightning supports the parallel import of a single table or multiple tables. By simultaneously running multiple TiDB Lightning instances, you can import data from single or multiple tables in parallel. In this way, TiDB Lightning provides the ability to scale horizontally, which greatly reduces the time required to import large amount of data.
 
 In technical implementation, TiDB Lightning records the meta data of each instance and the data of each imported table in the target TiDB, and coordinates the Row ID allocation range of different instances, the record of global Checksum, and the configuration changes and recovery of TiKV and PD.
 

tidb-lightning/tidb-lightning-physical-import-mode.md

@@ -74,7 +74,7 @@ It is recommended that you allocate CPU more than 32 cores and memory greater th
 
 - Do not use the physical import mode to directly import data to TiDB clusters in production. It has severe performance implications. If you need to do so, refer to [Pause scheduling on the table level](/tidb-lightning/tidb-lightning-physical-import-mode-usage.md#scope-of-pausing-scheduling-during-import).
 - If your TiDB cluster has a latency-sensitive application and a low concurrency, it is strongly recommended that you **do not** use the physical import mode to import data into the cluster. This mode might have significant impact on the online application.
-- Do not use multiple TiDB Lightning instances to import data to the same TiDB cluster by default. Use [Parallel Import](/tidb-lightning/tidb-lightning-distributed-import.md) instead.
+- If you want to run multiple TiDB Lightning instances simultaneously to import data into the same TiDB cluster, you can enable [Parallel Import](/tidb-lightning/tidb-lightning-distributed-import.md) to coordinate the import. If each instance imports data into **different tables**, the Parallel Import option is not required. However, if multiple instances import data into **the same table**, you need to enable Parallel Import to prevent conflicts and ensure data integrity.
 - When you use multiple TiDB Lightning to import data to the same target cluster, do not mix the import modes. That is, do not use the physical import mode and the logical import mode at the same time.
 - During the process of importing data, do not perform DDL and DML operations in the target table. Otherwise the import will fail or the data will be inconsistent. At the same time, it is not recommended to perform read operations, because the data you read might be inconsistent. You can perform read and write operations after the import operation is completed.
 - A single Lightning process can import a single table of 10 TiB at most. Parallel import can use 10 Lightning instances at most.