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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
[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)
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.
Is there an official explanation of the principles?
Setting it to 2 is just a waste.
I saw before that having 2 replicas is for high availability.
For MPP, having 2 replicas compared to 1 replica also improves performance, right?
My understanding is that with MPP, you don’t need to copy all the required nodes to other nodes.
It can handle a larger concurrency. The official statement says it supports up to 50 concurrent connections.
TiFlash multiple replicas cannot improve performance, only ensure availability.
You can search the official documentation or make good use of the forum search 
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.
Is it still usable after you stop a TiKV? And have you tested it yourself?
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.
The addition process does not affect the normal use of existing data.
Are you trying to find the exact wording from the official documentation?
You have already tested it yourself and it works, what other questions do you have?
It should be possible. During the expansion phase, the original cluster can continue to provide services normally, and the features should also be available.
Yes, the company requires an official statement to make changes.
Personally, I have no questions. The company has requested to find the official statement.
I didn’t see such an explanation in the official documentation.
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