Update Lightning import error handling (#13376) (#13395) (#13820)

sql-statements/sql-statement-admin-show-ddl.md

@@ -51,7 +51,10 @@ The `ADMIN SHOW DDL JOBS` statement is used to view all the results in the curre
 - `JOB_ID`: each DDL operation corresponds to a DDL job. `JOB_ID` is globally unique.
 - `DB_NAME`: the name of the database where the DDL operation is performed.
 - `TABLE_NAME`: the name of the table where the DDL operation is performed.
-- `JOB_TYPE`: the type of DDL operation.
+- `JOB_TYPE`: the type of DDL operation. Common job types include the following:
+    - `ingest`: Ingestion with accelerated index backfilling as configured by [`tidb_ddl_enable_fast_reorg`](/system-variables.md#tidb_ddl_enable_fast_reorg-new-in-v630).
+    - `txn`: Basic transactional backfill.
+    - `txn-merge`: Transactional backfill with a temporary index that gets merged with the original index when the backfill is finished.
 - `SCHEMA_STATE`: the current state of the schema object that the DDL operates on. If `JOB_TYPE` is `ADD INDEX`, it is the state of the index; if `JOB_TYPE` is `ADD COLUMN`, it is the state of the column; if `JOB_TYPE` is `CREATE TABLE`, it is the state of the table. Common states include the following:
     - `none`: indicates that it does not exist. Generally, after the `DROP` operation or after the `CREATE` operation fails and rolls back, it will become the `none` state.
     - `delete only`, `write only`, `delete reorganization`, `write reorganization`: these four states are intermediate states. For their specific meanings, see [How the Online DDL Asynchronous Change Works in TiDB](/ddl-introduction.md#how-the-online-ddl-asynchronous-change-works-in-tidb). As the intermediate state conversion is fast, these states are generally not visible during operation. Only when performing `ADD INDEX` operation can the `write reorganization` state be seen, indicating that index data is being added.

system-variables.md

@@ -1139,6 +1139,10 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
 > - When the index adding job starts first, it prevents the log backup job of PITR from starting by throwing an error, which does not affect the index adding job in progress. After the index adding job is completed, you need to restart the log backup job and perform a full backup manually.
 > - When a log backup job of PITR and an index adding job start at the same time, no error is prompted because the two jobs are unable to detect each other. PITR does not back up the newly added index. After the index adding job is completed, you still need to restart the log backup job and perform a full backup manually.
 
+> **Note:**
+>
+> Index acceleration requires a [`temp-dir`](/tidb-configuration-file.md#temp-dir-new-in-v630) that is writable and has enough free space. If the `temp-dir` is unusable, TiDB falls back to non-accelerated index building. It is recommended to put the `temp-dir` on a SSD disk.
+
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