Is the TiFlash feature available during the process of expanding a TiFlash table from 1 replica to 2 replicas?

Note:
This topic has been translated from a Chinese forum by GPT and might contain errors.

Original topic: TiFlash 表从1副本扩容到2副本过程,tiflash特性可用么

| username: TiDBer_yyy

[TiDB Usage Environment] Production Environment
[TiDB Version] 7.1.0
[Reproduction Path] None
[Encountered Problem: Problem Phenomenon and Impact]
The tiflash synchronization of 1 replica is in the AVAILABLE=1 state, and it needs to be expanded to 2 replicas to ensure HA.

Question:
Is the tiflash feature of the table available during the expansion process?

Additional note, it can be used in the self-test process. Do any experts have actual operation cases?
tiflash expand from 1 replica to 2 replicas tiflash feature available.log (30.7 KB)

| username: h5n1 | Original post link

There is already a complete copy, just adding another one, increasing the region from 1 Learner to 2. The original one can of course be used.

| username: TiDBer_yyy | Original post link

Is there an official explanation of the principles?

| username: 芮芮是产品 | Original post link

Setting it to 2 is just a waste.

| username: TiDBer_yyy | Original post link

I saw before that having 2 replicas is for high availability.

| username: tidb菜鸟一只 | Original post link

For MPP, having 2 replicas compared to 1 replica also improves performance, right?

| username: TiDBer_yyy | Original post link

My understanding is that with MPP, you don’t need to copy all the required nodes to other nodes.

| username: zhanggame1 | Original post link

It can handle a larger concurrency. The official statement says it supports up to 50 concurrent connections.

| username: h5n1 | Original post link

TiFlash multiple replicas cannot improve performance, only ensure availability.

| username: ShawnYan | Original post link

You can search the official documentation or make good use of the forum search :stuck_out_tongue_winking_eye:

| username: TiDBer_yyy | Original post link

111, the original question is still about whether TiFlash is available during the process of increasing from 1 replica to 2 replicas, and if there is any official clarification on this.

| username: h5n1 | Original post link

Is it still usable after you stop a TiKV? And have you tested it yourself?

| username: 大飞哥online | Original post link

During the scaling process, TiFlash will automatically copy data from TiKV to the new TiFlash replicas to ensure data consistency. So, during the TiFlash scaling process, the TiFlash feature of the table is available, and you can continue to use the TiFlash replicas for queries and analysis, but the data might not be the latest.

| username: Jellybean | Original post link

The addition process does not affect the normal use of existing data.

| username: ShawnYan | Original post link

Are you trying to find the exact wording from the official documentation?

| username: 像风一样的男子 | Original post link

You have already tested it yourself and it works, what other questions do you have?

| username: 随缘天空 | Original post link

It should be possible. During the expansion phase, the original cluster can continue to provide services normally, and the features should also be available.

| username: TiDBer_yyy | Original post link

Yes, the company requires an official statement to make changes.

| username: TiDBer_yyy | Original post link

Personally, I have no questions. The company has requested to find the official statement.

| username: heiwandou | Original post link

I didn’t see such an explanation in the official documentation.