[tarantool-patches] Re: [PATCH 6/6] [RAW] swim: introduce failure detection component

[Konstantin Osipov <kostja@tarantool.org>]

* Vladislav Shpilevoy <v.shpilevoy@tarantool.org> [19/03/20 14:11]:
>  
>  
> +/**
> + * Decode a failure detection message. Schedule acks, process
> + * acks.
> + */
> +static int
> +swim_process_failure_detection(struct swim *swim, const char **pos,
> +			       const char *end, const struct sockaddr_in *src,
> +			       const struct tt_uuid *uuid)
> +{
> +	const char *prefix = "invalid failure detection message:";
> +	struct swim_failure_detection_def def;
> +	struct swim_member_def mdef;
> +	if (swim_failure_detection_def_decode(&def, pos, end, prefix) != 0)
> +		return -1;
> +	say_verbose("SWIM %d: process failure detection's %s", swim_fd(swim),
> +		    swim_fd_msg_type_strs[def.type]);
> +	swim_member_def_create(&mdef);
> +	mdef.addr = *src;
> +	mdef.incarnation = def.incarnation;
> +	mdef.uuid = *uuid;
> +	struct swim_member *member = swim_upsert_member(swim, &mdef);
> +	if (member == NULL)
> +		return -1;
> +	if (def.incarnation < member->incarnation)
> +		return 0;

I think this branch a comment. Why do you not respond to pings
from older incarnations?

> +	if (no_acks_to_gc >= 0)
> +		swim->no_acks_to_gc = no_acks_to_gc;

Why do you actually need a custom no_acks_to_gc? Could you please
add a comment for this variable declaration?

> +enum {
> +	/**
> +	 * Value being used to say that unacknowledged pings
> +	 * should not affect a certain decision about member. For
> +	 * example, regardless of number of unacked pings, never
> +	 * drop a member.
> +	 */
> +	SWIM_NO_ACKS_IGNORE = INT_MAX,
> +};

OK, now I get it. You use it to pin members. I would actually use
bool is_pinned for that. It seems you make no_acks_to_gc a
variable only to use it for pinning. Let's add a separate varaible
for pins.

> +/**
> + * Send a ping to this address. If an ACK is received, the member
> + * will be added.

Could you also please explain in the comment why this is useful?
E.g. why would I want to add a member only after a successful
ping/ack?

> + */
> +int
> +swim_probe_member(struct swim *swim, const char *uri);
> +
> +	SWIM_FD_MSG_TYPE,

The patch is generally OK to push after fixing the minor comments
above. I also changed a few comments on the branch.

-- 
Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov