log_ratelimit: allow to completely disable

From now on log_ratelimiter can be completely disabled by setting
`vshard.consts.LOG_RATELIMIT_INTERVAL` to 0. It's done for users, who
don't want to use ratelimiter at all.

Part of #606

NO_DOC=internal

Author: Serpentian

test/unit-luatest/log_ratelimit_test.lua

@@ -1,6 +1,7 @@
 local t = require('luatest')
 local server = require('test.luatest_helpers.server')
 local verror = require('vshard.error')
+local vconsts = require('vshard.consts')
 local vratelimit = require('vshard.log_ratelimit')
 
 local test_group = t.group('log_ratelimit')
@@ -76,3 +77,24 @@ test_group.test_garbage_collection = function()
     collectgarbage()
     t.assert_not(vratelimit.internal.limiters[name])
 end
+
+test_group.test_disable_ratelimit = function()
+    local old_interval = vconsts.LOG_RATELIMIT_INTERVAL
+    vconsts.LOG_RATELIMIT_INTERVAL = 0.1
+    local limiter = vratelimit.create({name = 'test_disable_ratelimit'})
+
+    local err = verror.box(box.error.new(box.error.NO_CONNECTION))
+    limiter:log_error(err)
+    t.assert(limiter.map[err.type][err.code])
+    limiter:log_error(err)
+    t.assert_equals(limiter.map[err.type][err.code].suppressed, 1)
+    -- Now limiter is disabled right in the middle of work.
+    vconsts.LOG_RATELIMIT_INTERVAL = 0
+    t.helpers.retrying({}, function()
+        -- Errors are not suppressed, old suppressed entries are flushed.
+        limiter:log_error(err)
+        t.assert_not(limiter.map[err.type])
+    end)
+
+    vconsts.LOG_RATELIMIT_INTERVAL = old_interval
+end

vshard/log_ratelimit.lua

@@ -110,6 +110,11 @@ end
 local function ratelimit_log_template(log_lvl)
     return function (limiter, entry, format, ...)
         ratelimit_flush(limiter)
+        if consts.LOG_RATELIMIT_INTERVAL <= 0 then
+            -- Ratelimiter is disabled.
+            log[log_lvl](format, ...)
+            return
+        end
         local level = 'verbose'
         local signed_entry = ratelimit_sign_entry(entry)
         if signed_entry.type and signed_entry.code then