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

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

On Wed, Oct 24, 2018 at 01:14:31PM +0300, Olga Arkhangelskaia wrote:
> Due to incorrect configuration comparison, some options, especially
> replication were reseted and restarted, despite that change did not
> actually happened. The patch fixes it.
> 
> 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
> 
>  src/box/lua/load_cfg.lua       |  43 +++++++++++++++--
>  test/replication/misc.result   | 106 +++++++++++++++++++++++++++++++++++++++++
>  test/replication/misc.test.lua |  38 +++++++++++++++
>  3 files changed, 183 insertions(+), 4 deletions(-)
> 
> diff --git a/src/box/lua/load_cfg.lua b/src/box/lua/load_cfg.lua
> index df0c3c6ae..98d7ff47c 100644
> --- a/src/box/lua/load_cfg.lua
> +++ b/src/box/lua/load_cfg.lua
> @@ -365,6 +365,41 @@ local function apply_default_cfg(cfg, default_cfg)
>      end
>  end
>  
> +-- Compare given  config with old one.
> +-- Returns true if new config is similar to old one, false otherwise.

Nit: empty space between 'given' and 'config'. Articles are missing.
You should use 'equivalent' instead of 'similar' here.

> +local function compare_cfg(cfg1, cfg2)
> +    if type(cfg1) ~= "table" and type(cfg2) ~= "table" then
> +	return cfg1 == cfg2
> +    end
> +    if type(cfg1) == "table" and type(cfg2) ~= "table" then
> +        if table.getn(cfg1) ~= 1 then

table.getn is deprecated, you should use # instead

> +            return false
> +        else
> +            if type(cfg1[1]) ~= "nil" and type(cfg2) ~= "nil" then
> +                return string.formagt(cfg1[1]) == string.format(cfg2)
> +            else return cfg1[1] == cfg2 end
> +        end
> +    end
> +    if type(cfg2) == "table" and type(cfg1) ~= "table" then
> +	if table.getn(cfg2) ~= 1 then
> +            return false
> +        else
> +            if type(cfg2[1]) ~= "nil" and type(cfg1) ~= "nil" then
> +                return string.format(cfg2[1]) == string.format(cfg1)
> +            else return cfg2[1] == cfg1 end
> +        end
> +    end

I don't think you should interpret the table content anyhow here, i.e.
convert values to string or treat a table of one element as a raw value,
because although this is valid for box.cfg.replication, this may be not
for other configuration options. This work should be done by modify_cfg.

> +    if type(cfg1) == "table" and type(cfg2) == "table" then
> +        if table.getn(cfg1) ~= table.getn(cfg2) then return false end
> +        table.sort(cfg1)
> +        table.sort(cfg2)
> +        for key in pairs(cfg1) do
> +	    if not compare_cfg(cfg1[key], cfg2[key]) then return false end
> +        end
> +	return true

Bad indentation.

Anyway, this is a rather peculiar way of comparing tables. What if a
table contains subtables or string keys? How table.sort() is going to
work then? Please google a correct way of comparing Lua tables.

> +    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)
> @@ -375,9 +410,9 @@ local function reload_cfg(oldcfg, cfg)
>          end
>      end
>      for key in pairs(cfg) do
> -        local val = newcfg[key]
> -        local oldval = oldcfg[key]
> -        if oldval ~= val then
> +	if not compare_cfg(oldcfg[key], newcfg[key]) then
> +            local val = newcfg[key]
> +            local oldval = oldcfg[key]

Please try to keep your diff as small as possible. Here you could simply

         local val = newcfg[key]
         local oldval = oldcfg[key]
-        if oldval ~= val then
+        if not compare_cfg(oldval, val) then
             rawset(oldcfg, key, val)

Also, you should use compare_cfg() in load_cfg() too.

>              rawset(oldcfg, key, val)
>              if not pcall(dynamic_cfg[key]) then
>                  rawset(oldcfg, key, oldval) -- revert the old value
> @@ -388,7 +423,7 @@ local function reload_cfg(oldcfg, cfg)
>              end
>              log.info("set '%s' configuration option to %s", key,
>                  json.encode(val))
> -        end
> +        else log.info("option '%s' has not change", key) end

We silently skipped unmodified options before. I don't think we need to
log them now.

>      end
>      if type(box.on_reload_configuration) == 'function' then
>          box.on_reload_configuration()
> diff --git a/test/replication/misc.test.lua b/test/replication/misc.test.lua
> index 46726b7f4..96274b263 100644
> --- a/test/replication/misc.test.lua
> +++ b/test/replication/misc.test.lua
> @@ -191,3 +191,41 @@ 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")
> +
> +test_run:grep_log('replica', 'replication')
> +replication = box.cfg.replication
> +box.cfg{replication = {replication}}
> +test_run:grep_log('replica', 'has not change') ~= nil
> +test_run:grep_log('replica', "set 'replication' configuration option to") == nil
> +box.cfg{replication = replication}
> +test_run:grep_log('replica', "set 'replication' configuration option to") == nil

There's a better way to check if this works: revoke replication grants
on the master and try to reconfigure replication on the replica.


> +
> +test_run:cmd("switch default")
> +test_run:cmd('stop server replica')
> +test_run:cmd('cleanup server test')
> +test_run:cmd("start server replica")
> +test_run:cmd("switch replica")
> +
> +listen = box.cfg.listen
> +replication = box.cfg.replication
> +
> +box.cfg{replication = {replication, listen}}
> +test_run:grep_log('replica', "set 'replication' configuration option to")
> +test_run:grep_log('replica', "has not change") == nil
> +box.cfg{replication = {listen, replication}}
> +test_run:grep_log('replica', "has not change") ~= nil
> +
> +test_run:cmd("switch default")
> +test_run:cmd("stop server replica")
> +test_run:cmd("cleanup server replica")
> +test_run:cmd("delete server replica")
> +box.schema.user.revoke('guest', 'replication')