Some Questions About Enabling TiFlash Functionality

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

Original topic: 启用TiFlash 功能的一些疑问

| username: Echo_404

Just started using TiDB and would like to ask some questions to everyone. I have read the documentation for a long time and searched the Q&A in the forum, but I still have some doubts.

TiFlash Activation Issue:
According to the documentation, whether TiFlash is deployed uniformly by tiup or added later, does it mean that TiFlash functionality can only be enabled after manually setting up and creating TiFlash replicas?

Replica Issue:
What does the replica (count) mentioned in the documentation mean? If I deploy 3 TiFlash instances, is creating 1 replica sufficient? My understanding is that multiple replicas are equivalent to backups. When there are 2 or more counts, if any one TiFlash instance fails, the existence of multiple replicas ensures that subsequent usage is not affected. Is this understanding correct?

After manually creating TiFlash replicas, will subsequent changes to tables and databases in TiKV be automatically synchronized? No need for manual updates?

Thank you all for your answers.

| username: xfworld | Original post link

  • TiFlash is an MPP engine, not mandatory (resource-intensive), optional (choose suitable scenarios).

  • All data synchronization requires selection, essentially setting a rule and scope for automatic data synchronization.

  • The number of replicas is not “count,” but “number of replicas,” referring to how many copies of the data exist. If one replica is lost, another can still function. TiFlash’s performance won’t improve with more replicas; it will only waste more space. Generally, two replicas are sufficient.

  • It’s important to understand the differences between row storage and column storage, as well as their usage methods and suitable scenarios.

| username: ShawnYan | Original post link

Yes, so generally you only need to specify a few tables that need to be used at the beginning, and then the table structure and data will be automatically synchronized.

As mentioned above, it is generally sufficient to deploy 2 TiFlash nodes and create 2 replicas to prevent a single point of failure.

| username: Echo_404 | Original post link

Okay, got it. Thank you for the explanation. :blush:

| username: Echo_404 | Original post link

Got it, thanks for the explanation. Now I understand. :blush:

| username: system | Original post link

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