[tarantool-patches] Re: [PATCH 2/2] Fix discovery/reconfigure race

[Vladislav Shpilevoy]

Thanks for the patch! See 5 comments below.

On 15/06/2018 15:47, AKhatskevich wrote:
> This commit prevents discovery fiber from discovering old replicasets
> and spoiling `route_map`.
> ---
>   test/router/router.result   | 62 +++++++++++++++++++++++++++++++++++++++++++++
>   test/router/router.test.lua | 42 ++++++++++++++++++++++++++++++
>   vshard/router/init.lua      | 15 ++++++++++-
>   3 files changed, 118 insertions(+), 1 deletion(-)
> 
> diff --git a/test/router/router.result b/test/router/router.result
> index 5643f3e..e61505e 100644
> --- a/test/router/router.result
> +++ b/test/router/router.result
> @@ -1095,6 +1095,68 @@ for bucket, old_rs in pairs(bucket_to_old_rs) do
>   end;
>   ---
>   ...
> +--
> +-- Check route_map is not filled with old replica objects after
> +-- recpnfigure.

1. Typo.

> +--
> +-- Perform #replicasets phases of discovery, to update replicasets
> +-- object in for loop of discovery fiber since previous cfg.
> +for _, __ in pairs(vshard.router.internal.replicasets) do
> +    vshard.router.discovery_wakeup()
> +    fiber.sleep(0.02)
> +end;
> +---
> +...
> +-- Simulate long `callro`.
> +-- Stuck on first rs in replicasets.
> +vshard.router.internal.errinj.LONG_DISCOVERY = true;

2. I do not see this error injection in the M.errinj
declaration.

> +---
> +...
> +for _, __ in pairs(vshard.router.internal.replicasets) do
> +    vshard.router.discovery_wakeup()
> +    fiber.sleep(0.02)
> +end;

3. This cycle makes no sense. With set LONG_DISCOVERY it is
equivalent to calling router.discovery_wakeup() once.

> +---
> +...
> +vshard.router.cfg(cfg);
> +---
> +...
> +vshard.router.internal.errinj.LONG_DISCOVERY = nil;
> +---
> +...
> +-- Do discovery iteration.
> +vshard.router.discovery_wakeup()
> +fiber.sleep(0.02)

4. Concrete timeouts are the way to create an unstable test.
Please, get rid of them and replace with 'while not cond do wait end'
where necessary.

> +
> +rs_cnt = 0;
> +---
> +...
> +new_replicasets = {}
> +for _, rs in pairs(vshard.router.internal.replicasets) do
> +    new_replicasets[rs] = true
> +    rs_cnt = rs_cnt + 1
> +end;
> +---
> +...
> +rs_cnt;
> +---
> +- 2
> +...
> +bucket_cnt = 0;
> +---
> +...
> +for bucket_id, rs in pairs(vshard.router.internal.route_map) do
> +    if not new_replicasets[rs] then> +        error('Old object added to route_map.')
> +    end
> +    bucket_cnt = bucket_cnt + 1
> +end;
> +---
> +...
> +bucket_cnt;
> +---
> +- 3000
> +...
>   test_run:cmd("setopt delimiter ''");
>   ---
>   - true
> diff --git a/vshard/router/init.lua b/vshard/router/init.lua
> index 7e765fa..df5b343 100644
> --- a/vshard/router/init.lua
> +++ b/vshard/router/init.lua
> @@ -127,10 +127,23 @@ local function discovery_f(module_version)
>       local iterations_until_lua_gc =
>           consts.COLLECT_LUA_GARBAGE_INTERVAL / consts.DISCOVERY_INTERVAL
>       while module_version == M.module_version do
> -        for _, replicaset in pairs(M.replicasets) do
> +        local old_replicasets = M.replicasets
> +        for rs_uuid, replicaset in pairs(M.replicasets) do
>               local active_buckets, err =
>                   replicaset:callro('vshard.storage.buckets_discovery', {},
>                                     {timeout = 2})
> +            while M.errinj.LONG_DISCOVERY do
> +                -- Stuck on the first replicaset.
> +                if rs_uuid ~= select(1, next(M.replicasets)) then
> +                    break
> +                end
> +                lfiber.sleep(0.01)
> +            end
> +            -- Renew replicasets object in case of reconfigure
> +            -- and reload events.

5. You do not renew here anything.

> +            if M.replicasets ~= old_replicasets then
> +                break
> +            end
>               if not active_buckets then
>                   log.error('Error during discovery %s: %s', replicaset, err)
>               else
>