RE: [Proposal] Add foreign-server health checks infrastructure

Dear Zhihong,

Thank you for reviewing! And I have to apologize for the late.
I'll post new patchset later.

> +       UnregisterAllCheckingRemoteServersCallback();
> 
> UnregisterAllCheckingRemoteServersCallback
> -> UnregisterAllCheckingRemoteServersCallbacks

Will fix.

> +   CheckingRemoteServersCallbackItem *item;
> +   item = fdw_callbacks;
> 
> The above two lines can be combined.

Will fix.

> +UnregisterCheckingRemoteServersCallback(CheckingRemoteServersCallback
> callback,
> +                                       void *arg)
> 
> Is the above func called anywhere ?

Currently not, I just kept the API because of any other FDW extensions.
But I cannot find any use cases, so will remove.

> +       if (item->callback == callback && item->arg == arg)
> 
> Is comparing argument pointers stable ? What if the same argument is cloned
> ?

This part is no longer needed. Will remove.

> +           CallCheckingRemoteServersCallbacks();
> +
> +           if (remote_servers_connection_check_interval > 0)
> +               enable_timeout_after(CHECKING_REMOTE_SERVERS_TIMEOUT,
> +
>  remote_servers_connection_check_interval);
>
> Should the call to CallCheckingRemoteServersCallbacks() be placed under the
> if block checking remote_servers_connection_check_interval ?
> If remote_servers_connection_check_interval is 0, it seems the callbacks
> shouldn't be called.

Agreed. We force stopping timeout when the GUC sets to 0 in assign_hook,
so your saying is consistent. Will move.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED