br: modify the faqs of pitr (pingcap#16096)

Author: enkilee

faq/backup-and-restore-faq.md

@@ -41,14 +41,6 @@ Currently, the log backup feature is not fully adapted to TiDB Lightning. Theref
 
 In upstream clusters where you create log backup tasks, avoid using the TiDB Lightning physical mode to import data. Instead, you can use TiDB Lightning logical mode. If you do need to use the physical mode, perform a snapshot backup after the import is complete, so that PITR can be restored to the time point after the snapshot backup.
 
-### Why is the acceleration of adding indexes feature incompatible with PITR?
-
-Issue: [#38045](https://github.com/pingcap/tidb/issues/38045)
-
-Currently, index data created through the [index acceleration](/system-variables.md#tidb_ddl_enable_fast_reorg-new-in-v630) feature cannot be backed up by PITR.
-
-Therefore, after PITR recovery is complete, BR will delete the index data created by index acceleration, and then recreate it. If many indexes are created by index acceleration or the index data is large during the log backup, it is recommended to perform a full backup after creating the indexes.
-
 ### The cluster has recovered from the network partition failure, but the checkpoint of the log backup task progress still does not resume. Why?
 
 Issue: [#13126](https://github.com/tikv/tikv/issues/13126)
@@ -57,16 +49,6 @@ After a network partition failure in the cluster, the backup task cannot continu
 
 To resolve this issue, you need to manually execute the `br log resume` command to resume the log backup task.
 
-### What should I do if the error `execute over region id` is returned when I perform PITR?
-
-Issue: [#37207](https://github.com/pingcap/tidb/issues/37207)
-
-This issue usually occurs when you enable log backup during a full data import and afterward perform a PITR to restore data at a time point during the data import.
-
-Specifically, there is a probability that this issue occurs if there are a large number of hotspot writes for a long time (such as 24 hours) and if the OPS of each TiKV node is larger than 50k/s (you can view the metrics in Grafana: **TiKV-Details** -> **Backup Log** -> **Handle Event Rate**).
-
-It is recommended that you perform a snapshot backup after the data import and perform PITR based on this snapshot backup.
-
 ## After restoring a downstream cluster using the `br restore point` command, data cannot be accessed from TiFlash. What should I do?
 
 Currently, PITR does not support writing data directly to TiFlash during the restore phase. Instead, br command-line tool executes the `ALTER TABLE table_name SET TIFLASH REPLICA ***` DDL to replicate the data. Therefore, TiFlash replicas are not available immediately after PITR completes data restore. Instead, you need to wait for a certain period of time for the data to be replicated from TiKV nodes. To check the replication progress, check the `progress` information in the `INFORMATION_SCHEMA.tiflash_replica` table.

system-variables.md

@@ -1586,10 +1586,6 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 
 <CustomContent platform="tidb">
 
-> **Warning:**
->
-> Currently, PITR recovery handles the indexes created by index acceleration during the log backup with extra processing to achieve compatibility. For details, see [Why is the acceleration of adding indexes feature incompatible with PITR?](/faq/backup-and-restore-faq.md#why-is-the-acceleration-of-adding-indexes-feature-incompatible-with-pitr).
-
 > **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.
@@ -1603,8 +1599,6 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 > **Warning:**
 >
 > Currently, this feature is not fully compatible with [altering multiple columns or indexes in a single `ALTER TABLE` statement](/sql-statements/sql-statement-alter-table.md). When adding a unique index with the index acceleration, you need to avoid altering other columns or indexes in the same statement.
->
-> Currently, PITR recovery handles the indexes created by index acceleration during the log backup with extra processing to achieve compatibility. For details, see [Why is the acceleration of adding indexes feature incompatible with PITR?](https://docs.pingcap.com/tidb/v7.0/backup-and-restore-faq#why-is-the-acceleration-of-adding-indexes-feature-incompatible-with-pitr).
 
 </CustomContent>