Tikv: Support adjusting Slow log threshold dynamically

[breeswish]

Development Task

In https://github.com/tikv/tikv/pull/9061 a slow log config item is added. It can be further extended to support dynamic modification.

A dynamic config modification is performed from TiKV-Control command line (documentation)

[idoqo]

Hi @breeswish, I'm trying to get familiar with tikv ahead of GSoC and wanted to give this a shot. Do you mind helping with some pointers?

I don't know if it's right but it seems based on this, that configs under the server field are marked as "skip" and cannot be modified dynamically at the moment.

[NingLin-P]

Hi @idoqo #[config(skip)] is used to check if we try to change a config that not support changing dynamically. To support changing server.end_point_slow_log_threshold dynamically, we need to replace #[config(skip)] with #[config(submodule)] for server and which will require server::Config to derive the Configuration trait and to dispatch the changes to where the config actually used, we also need to implement a ConfigManager. Take backup for example, here is what we need to do:

https://github.com/tikv/tikv/blob/0632bd27a0062a2e21e0cdc88753a9f906f85fbe/src/config.rs#L2261-L2262
https://github.com/tikv/tikv/blob/0632bd27a0062a2e21e0cdc88753a9f906f85fbe/src/config.rs#L2145-L2150
https://github.com/tikv/tikv/blob/0632bd27a0062a2e21e0cdc88753a9f906f85fbe/components/backup/src/endpoint.rs#L379-L387
https://github.com/tikv/tikv/blob/0632bd27a0062a2e21e0cdc88753a9f906f85fbe/cmd/src/server.rs#L800-L803
https://github.com/tikv/tikv/blob/0632bd27a0062a2e21e0cdc88753a9f906f85fbe/components/backup/src/endpoint.rs#L779

[idoqo]

@NingLin-P @breeswish

I've created a draft PR for this but I'm still a bit confused about a few things. For example:

• I'm correctly binding the server Config to the ServerConfigManager with Arc<RwLock<Config>>, but I'm not sure if it's the right way to do that.

• Should we mark all the other fields of the server Config struct as skip, since endpoint-slow-log-threshold is the only one we want to make changeable (for now).

[NingLin-P]

@idoqo

I'm correctly binding the server Config to the ServerConfigManager with Arc>, but I'm not sure if it's the right way to do that.

It is okay to use Arc<RwLock<Config>>

Should we mark all the other fields of the server Config struct as skip, since endpoint-slow-log-threshold is the only one we want to make changeable (for now).

Yes, we need to mark all the other fields of the server Config struct as skip

[idoqo]

Yes, we need to mark all the other fields of the server Config struct as skip

Alright, thanks a lot! I've marked the PR as ready for review now (though I haven't been able to figure out why the CI is failing).