From e77db7dd6dcf40fce60dced1c6c5d0926621c54b Mon Sep 17 00:00:00 2001 From: houfaxin Date: Mon, 31 Mar 2025 19:31:16 +0800 Subject: [PATCH 1/2] initial trans --- ticdc/ticdc-compatibility.md | 7 +++++++ tiflash/create-tiflash-replicas.md | 7 +++++++ 2 files changed, 14 insertions(+) diff --git a/ticdc/ticdc-compatibility.md b/ticdc/ticdc-compatibility.md index f142e3d6fbc40..112c0990f8dbb 100644 --- a/ticdc/ticdc-compatibility.md +++ b/ticdc/ticdc-compatibility.md @@ -28,6 +28,13 @@ In the physical import mode, TiDB Lightning imports data by inserting SST files 1. Use the offline import tool provided by your downstream system to import TiDB Lightning's input files. 2. Create a changefeed to replicate subsequent incremental data written through SQL. For more information, see [Create a replication task](/ticdc/ticdc-manage-changefeed.md#create-a-replication-task). +## Compatibility with TiFlash + +Currently, when you use TiCDC to replicate tables to a downstream TiDB cluster, creating TiFlash replicas for the tables is not supported, which means that TiCDC does not support replicating TiFlash-related DDL statements, such as: + +* `ALTER TABLE table_name SET TIFLASH REPLICA count;` +* `ALTER DATABASE db_name SET TIFLASH REPLICA count;` + ## CLI and configuration file compatibility * In TiCDC v4.0.0, `ignore-txn-commit-ts` is removed and `ignore-txn-start-ts` is added, which uses start_ts to filter transactions. diff --git a/tiflash/create-tiflash-replicas.md b/tiflash/create-tiflash-replicas.md index ca9f08e3261e4..f216bbb4cabee 100644 --- a/tiflash/create-tiflash-replicas.md +++ b/tiflash/create-tiflash-replicas.md @@ -53,6 +53,11 @@ ALTER TABLE `tpch50`.`lineitem` SET TIFLASH REPLICA 0; * In v5.1 and later versions, setting the replicas for the system tables is no longer supported. Before upgrading the cluster, you need to clear the replicas of the relevant system tables. Otherwise, you cannot modify the replica settings of the system tables after you upgrade the cluster to a later version. +* Currently, when you use TiCDC to replicate tables to a downstream TiDB cluster, creating TiFlash replicas for the tables is not supported, which means that TiCDC does not support replicating TiFlash-related DDL statements, such as: + + * `ALTER TABLE table_name SET TIFLASH REPLICA count;` + * `ALTER DATABASE db_name SET TIFLASH REPLICA count;` + ### Check replication progress You can check the status of the TiFlash replicas of a specific table using the following statement. The table is specified using the `WHERE` clause. If you remove the `WHERE` clause, you will check the replica status of all tables. @@ -103,6 +108,8 @@ Examples: > > - This statement skips system tables, views, temporary tables, and tables with character sets not supported by TiFlash. +> - You can control the number of tables allowed to remain unavailable during execution by setting the [`tidb_batch_pending_tiflash_count`](/system-variables.md/#tidb_batch_pending_tiflash_count-new-in-v60) system variable. Lowering this value helps reduce the pressure on the cluster during replication. Note that this limit is not real-time, so it is still possible for the number of unavailable tables to exceed the limit after the setting is applied. + ### Check replication progress Similar to creating TiFlash replicas for tables, successful execution of the DDL statement does not mean the completion of replication. You can execute the following SQL statement to check the progress of replication on target tables: From 02f0db09a5798b2a746501fdb4f4c0cd1057d734 Mon Sep 17 00:00:00 2001 From: xixirangrang Date: Tue, 1 Apr 2025 14:10:08 +0800 Subject: [PATCH 2/2] Update tiflash/create-tiflash-replicas.md --- tiflash/create-tiflash-replicas.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tiflash/create-tiflash-replicas.md b/tiflash/create-tiflash-replicas.md index f216bbb4cabee..ad45079d8a2de 100644 --- a/tiflash/create-tiflash-replicas.md +++ b/tiflash/create-tiflash-replicas.md @@ -108,7 +108,7 @@ Examples: > > - This statement skips system tables, views, temporary tables, and tables with character sets not supported by TiFlash. -> - You can control the number of tables allowed to remain unavailable during execution by setting the [`tidb_batch_pending_tiflash_count`](/system-variables.md/#tidb_batch_pending_tiflash_count-new-in-v60) system variable. Lowering this value helps reduce the pressure on the cluster during replication. Note that this limit is not real-time, so it is still possible for the number of unavailable tables to exceed the limit after the setting is applied. +> - You can control the number of tables allowed to remain unavailable during execution by setting the [`tidb_batch_pending_tiflash_count`](/system-variables.md#tidb_batch_pending_tiflash_count-new-in-v60) system variable. Lowering this value helps reduce the pressure on the cluster during replication. Note that this limit is not real-time, so it is still possible for the number of unavailable tables to exceed the limit after the setting is applied. ### Check replication progress