Document default values of the system parameters, and where to configure the values

[hengm3467]

Related code PR

risingwavelabs/risingwave#8623

Which part(s) of the docs might be affected or should be updated? And how?

Manage RisingWave -> Vieww and adjust system parameters

@Gun9niR As I understand it, we'll need to mention two things:

1. The default/initial values out of box (without customization by users)
2. Where to customize/specify the initial values

Correct? Or only the latter would be fine?

Thanks.

Reference

No response

[Gun9niR]

I think both are required. Some notes:

• While we can initialize the initial values from the config file (the [system] section), it is only for CI purposes and should not be used by the user.
• Immutable params can be initialized from CLI, e.g. state_store corresponds to --state-store and environment variable RW_STATE_STORE
• Mutable params can only be initialized with the default value. The user can modify it later with ALtER SYSTEM.

[hengm3467]

--> Immutable params can be initialized from CLI, e.g. state_store corresponds to --state-store and environment variable RW_STATE_STORE

@Gun9niR Can you share more information about how to do this? Thanks!

[Gun9niR]

The reason that immutable params need to be initialized from CLI is due to their immutability, ALTER SYSTEM SET on them will fail.

So we need to initialize them from command line arguments. For example, state_store is one of these immutable params, so to initialize it, one can add an argument --state-store=hummock-memory after the meta node command. Once the cluster is up, the user is not allowed to change it. One can also specify the environment variable RW_STATE_STORE to initialize it, which overrides CLI argument.

Once the cluster is started, the system parameters are persisted to meta store (etcd). If the meta node is restarted with different initial values for these params, they will just be ignored, and a warning message will be emitted.

[hengm3467]

Fixed in #981.