Re: [tarantool-patches] [PATCH v2] box: fixed comparison of old and new config options

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Tue, Oct 30, 2018 at 03:04:23PM +0300, Olga Arkhangelskaia wrote:
> Due to incorrect configuration comparison, some options, especially
> replication, were reseted and restarted, despite that configurations
> were equivalent.

Bad description. Please describe why exactly we're doing this, i.e. what
happens if we don't check whether box.cfg.replication actually changed.

> 
> Closes #3711
> ---
> Issue:
> https://github.com/tarantool/tarantool/issues/3711
> Branch:
> https://github.com/tarantool/tarantool/tree/OKriw/gh-3711-do-not-restart-replication-if-config-did-not-change-2.1
> 
> v1:
> https://www.freelists.org/post/tarantool-patches/PATCH-box-fixed-comparison-of-old-and-new-config-options
> 
> Changes in v2:
> - changed test
> - conversion from num to string now in modify_cfg
> - no sort table in comparison
> - got rid of table.getn
> 
>  src/box/lua/load_cfg.lua       | 33 +++++++++++++++++++--
>  test/replication/misc.result   | 65 ++++++++++++++++++++++++++++++++++++++++++
>  test/replication/misc.test.lua | 24 ++++++++++++++++
>  3 files changed, 119 insertions(+), 3 deletions(-)
> 
> diff --git a/src/box/lua/load_cfg.lua b/src/box/lua/load_cfg.lua
> index df0c3c6ae..6d3c7f62c 100644
> --- a/src/box/lua/load_cfg.lua
> +++ b/src/box/lua/load_cfg.lua
> @@ -145,7 +145,11 @@ local template_cfg = {
>  }
>  
>  local function normalize_uri(port)
> -    if port == nil or type(port) == 'table' then
> +    if port == nil then return port end

Nit: we never write 'then' and 'return' at the same line, please fix
here and everywhere.

> +    if type (port) == 'table' then
             ^^^
Nit: extra space

> +        for i in pairs(port) do
> +            port[i] = tostring(port[i])
> +        end
>          return port
>      end
>      return tostring(port);

This function is also used for normalizing box.cfg.listen, which can't
be a table. IMHO we'd better introduce normalize_uri_list instead of
patching it.

> @@ -365,6 +369,29 @@ local function apply_default_cfg(cfg, default_cfg)
>      end
>  end
>  
> +-- check whether two configurations are equivalent, returns true, if yes,
> +-- false otherwise.

Nit: we start comments with a capital letter and try to limit the text
width to ~65 symbols. Anyway, let's rewrite this comment to be as simple
as:

-- Return true if the two configurations are equivalent.

> +local function equivalent (t1, t2)

Please name this function compare_cfg() as you used to - this would be
consistent with load_cfg() and modify_cfg(). I wanted you to just fix
the comment.

> +    if type(t1) ~= 'table' and type(t2) ~= 'table' then return t1 == t2 end
> +    if type(t1) == "table" and type(t2) ~= "table" then

Nit: please use the same quote style ("" or '') everywhere.

> +        if #t1 == 1 then return t1[1] == t2 end

As I said, you should do all config interpretation in modify_cfg(),
in particular turning a scalar into a table if necessary.

> +        return false
> +    end
> +    if type(t2) == "table" and type(t1) ~= "table" then
> +        if #t2 == 1 then return t2[1] ==  t1 end
                                           ^^
Nit: extra space (it's very annoying, please self-review your code
before sending it for review).

> +        return false
> +    end
> +    if type(t1) == 'table' and type(t2) == 'table' then
> +        if #t1 ~= #t2 then return false end
> +        for i in pairs(t2) do
> +            if equivalent(t1[i], t2[i]) == false then

We don't use nested tables in configuration yet. Since this function
isn't generic anyway (it doesn't support Lua maps), I think we should
simplify it:

    for k, v in ipairs(t1) do
        if t2[k] ~= v then
            return false
        end
    end

> +                return false
> +            end
> +        end
> +        return true
> +    end
> +end
> +
>  local function reload_cfg(oldcfg, cfg)
>      cfg = upgrade_cfg(cfg, translate_cfg)
>      local newcfg = prepare_cfg(cfg, default_cfg, template_cfg, modify_cfg)
> @@ -377,7 +404,7 @@ local function reload_cfg(oldcfg, cfg)
>      for key in pairs(cfg) do
>          local val = newcfg[key]
>          local oldval = oldcfg[key]
> -        if oldval ~= val then
> +        if not equivalent(val, oldval) then
>              rawset(oldcfg, key, val)
>              if not pcall(dynamic_cfg[key]) then
>                  rawset(oldcfg, key, oldval) -- revert the old value
> @@ -452,7 +479,7 @@ local function load_cfg(cfg)
>          local val = cfg[key]
>          if val ~= nil and not dynamic_cfg_skip_at_load[key] then
>              fun()
> -            if val ~= default_cfg[key] then
> +            if not equivalent(val, default_cfg[key]) then
>                  log.info("set '%s' configuration option to %s", key, json.encode(val))
>              end
>          end
> diff --git a/test/replication/misc.test.lua b/test/replication/misc.test.lua
> index 46726b7f4..7a3020f6e 100644
> --- a/test/replication/misc.test.lua
> +++ b/test/replication/misc.test.lua
> @@ -191,3 +191,27 @@ test_run:cmd("stop server replica")
>  test_run:cmd("cleanup server replica")
>  test_run:cmd("delete server replica")
>  box.schema.user.revoke('guest', 'replication')
> +
> +
> +--
> +-- gh-3711 Do not restart replication on box.cfg if the configuration didn't change
> +--
> +box.schema.user.grant('guest', 'replication')
> +
> +test_run:cmd("create server replica with rpl_master=default, script='replication/replica.lua'")
> +test_run:cmd("start server replica")
> +test_run:cmd("switch replica")
> +replication = box.cfg.replication
> +test_run:cmd("switch default")
> +box.schema.user.revoke('guest', 'replication')

It would be nice if you described why you revoke replication privileges
here.

> +test_run:cmd("switch replica")

> +box.cfg{replication_sync_timeout = 0.5}

Why?

> +box.cfg{replication = {replication}}
> +box.info.status == 'running'
> +box.cfg{replication = replication}
> +box.info.status == 'running'

I want you to also check the case when box.cfg.replication is a table
of more than one element. You can use self as the second replication
source.

> +
> +test_run:cmd("switch default")
> +test_run:cmd("stop server replica")
> +test_run:cmd("cleanup server replica")
> +test_run:cmd("delete server replica")