Re: [Tarantool-patches] [PATCH 2/3] box/info: report replication.X.downstream.lag value

[Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

21.01.2021 20:17, Cyrill Gorcunov пишет:
> This is basically a reflection of replication.X.upstream.lag value.
> The upstream lag can be considered as transaction RTT in direction
> from master to replica, in turn downstream lag is the reverse and
> represents RTT from replica to master.
>
> An example of output is (on replica node)
>
>   | 2:
>   |   id: 2
>   |   uuid: 8bb22366-cd21-492e-98df-693884be11bd
>   |   lsn: 0
>   |   downstream:
>   |     status: follow
>   |     idle: 0.55381065199617
>   |     vclock: {1: 119}
>   |     lag: 0.00019168853759766
>
> In case if there some old replicas which are not sending
> timestamp in vclock encoding we simply don't show lag
> field for backward compatibility sake.
>
> Closes #5447
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
> ---

Hi! Thanks for the patch!
Please see a couple of nits below.

>   src/box/lua/info.c |  9 ++++++++-
>   src/box/relay.cc   | 17 +++++++++++++++++
>   src/box/relay.h    |  8 ++++++++
>   3 files changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/src/box/lua/info.c b/src/box/lua/info.c
> index c4c9fa0a0..b36c2e6f4 100644
> --- a/src/box/lua/info.c
> +++ b/src/box/lua/info.c
> @@ -132,17 +132,24 @@ lbox_pushrelay(lua_State *L, struct relay *relay)
>   	lua_pushstring(L, "status");
>   
>   	switch(relay_get_state(relay)) {
> -	case RELAY_FOLLOW:
> +	case RELAY_FOLLOW: {

The brace should go on a new line.

> +		double lag = relay_lag(relay);
>   		lua_pushstring(L, "follow");
>   		lua_settable(L, -3);
>   		lua_pushstring(L, "vclock");
>   		lbox_pushvclock(L, relay_vclock(relay));
>   		lua_settable(L, -3);
> +		if (lag != 0) {
> +			lua_pushstring(L, "lag");
> +			lua_pushnumber(L, relay_lag(relay));
> +			lua_settable(L, -3);
> +		}
>   		lua_pushstring(L, "idle");
>   		lua_pushnumber(L, ev_monotonic_now(loop()) -
>   			       relay_last_row_time(relay));
>   		lua_settable(L, -3);
>   		break;
> +	}
>   	case RELAY_STOPPED:
>   	{
>   		lua_pushstring(L, "stopped");



> @@ -558,6 +568,13 @@ relay_reader_f(va_list ap)
>   			/* vclock is followed while decoding, zeroing it. */
>   			vclock_create(&relay->recv_vclock);
>   			xrow_decode_vclock_xc(&xrow, &relay->recv_vclock);
> +			/*
> +			 * Old versions may send not a timestamp but
> +			 * zeroified memory field. We can use +0 as
> +			 * as sign that there is nothing encoded.

typo: as a sign.

> +			 */
> +			if (xrow.tm != 0)
> +				relay->lag = ev_now(loop()) - xrow.tm;
>   			fiber_cond_signal(&relay->reader_cond);
>   		}
>   	} catch (Exception *e) {
> diff --git a/src/box/relay.h b/src/box/relay.h
> index b32e2ea2a..ec9d16925 100644
> --- a/src/box/relay.h
> +++ b/src/box/relay.h
> @@ -93,6 +93,14 @@ relay_vclock(const struct relay *relay);
>   double
>   relay_last_row_time(const struct relay *relay);
>   
> +/**
> + * Returns relay's lag
> + * @param relay relay
> + * @returns relay's lag
> + */
> +double
> +relay_lag(const struct relay *relay);
> +
>   /**
>    * Send a Raft update request to the relay channel. It is not
>    * guaranteed that it will be delivered. The connection may break.

-- 
Serge Petrenko