test: allow to count select requests on storages

I don't want to lean on box.stat() information here, because I don't
control all iproto calls to storages: say, vshard rebalancer may perform
them in background.

Instead, I wrapped particular storage function I'm interested in.

The goal is to be able to determine how much storages is involved into a
select/pairs request.

Part of #220

test/entrypoint/srv_select.lua

@@ -192,6 +192,34 @@ package.preload['customers-storage'] = function()
     }
 end
 
+package.preload['statistics-storage'] = function()
+    return {
+        role_name = 'statistics-storage',
+        dependencies = {'cartridge.roles.crud-storage'},
+        init = function()
+            assert(_G._crud.select_on_storage ~= nil)
+
+            -- Here we count requests.
+            local storage_stat_table = {
+                select_requests = 0,
+            }
+
+            -- Wrap select_on_storage() function.
+            local select_on_storage_saved = _G._crud.select_on_storage
+            _G._crud.select_on_storage = function(...)
+                local requests = storage_stat_table.select_requests
+                storage_stat_table.select_requests = requests + 1
+                return select_on_storage_saved(...)
+            end
+
+            -- Accessor for the statistics.
+            rawset(_G, 'storage_stat', function()
+                return storage_stat_table
+            end)
+        end,
+    }
+end
+
 local box_opts = {
     readahead = 10 * 1024 * 1024,
 }
@@ -203,6 +231,7 @@ local ok, err = errors.pcall('CartridgeCfgError', cartridge.cfg, {
         'cartridge.roles.crud-router',
         'cartridge.roles.crud-storage',
         'customers-storage',
+        'statistics-storage',
     }},
     box_opts
 )

test/helper.lua

@@ -141,7 +141,14 @@ function helpers.truncate_space_on_cluster(cluster, space_name)
     end
 end
 
-function helpers.get_test_replicasets()
+function helpers.get_test_replicasets(opts)
+    local opts = opts or {}
+
+    local storage_roles = {'customers-storage', 'crud-storage'}
+    for _, role in ipairs(opts.extra_storage_roles or {}) do
+        table.insert(storage_roles, role)
+    end
+
     return {
         {
             uuid = helpers.uuid('a'),
@@ -154,7 +161,7 @@ function helpers.get_test_replicasets()
         {
             uuid = helpers.uuid('b'),
             alias = 's-1',
-            roles = { 'customers-storage', 'crud-storage' },
+            roles = storage_roles,
             servers = {
                 { instance_uuid = helpers.uuid('b', 1), alias = 's1-master' },
                 { instance_uuid = helpers.uuid('b', 2), alias = 's1-replica' },
@@ -163,7 +170,7 @@ function helpers.get_test_replicasets()
         {
             uuid = helpers.uuid('c'),
             alias = 's-2',
-            roles = { 'customers-storage', 'crud-storage' },
+            roles = storage_roles,
             servers = {
                 { instance_uuid = helpers.uuid('c', 1), alias = 's2-master' },
                 { instance_uuid = helpers.uuid('c', 2), alias = 's2-replica' },
@@ -230,4 +237,77 @@ function helpers.get_other_storage_bucket_id(cluster, bucket_id)
     ]], {bucket_id})
 end
 
+-- Determine a replicaset alias by a server object.
+function helpers.get_replicaset_alias(cluster, needle_server)
+    for _, replicaset in ipairs(cluster.replicasets) do
+        for _, server in ipairs(replicaset.servers) do
+            if server.alias == needle_server.alias then
+                return replicaset.alias
+            end
+        end
+    end
+    error(('Unable to find replicaset alias for server %s'):format(
+        needle_server.alias))
+end
+
+-- Accumulate statistics from given storages.
+--
+-- The statistics is grouped by replicasets.
+--
+-- Example of a return value:
+--
+-- {
+--     ['s-1'] = {
+--         select_requests = 1,
+--     },
+--     ['s-2'] = {
+--         select_requests = 0,
+--     },
+-- }
+function helpers.collect_storage_stat(cluster, aliases)
+    local res = {}
+
+    helpers.call_on_servers(cluster, aliases, function(server)
+        -- Collect the statistics.
+        local storage_stat = server.net_box:call('storage_stat')
+
+        -- Initialize if needed.
+        local replicaset_alias = helpers.get_replicaset_alias(cluster, server)
+        if res[replicaset_alias] == nil then
+            res[replicaset_alias] = {}
+        end
+
+        -- Accumulate the collected statistics.
+        for key, val in pairs(storage_stat) do
+            local old = res[replicaset_alias][key] or 0
+            res[replicaset_alias][key] = old + val
+        end
+    end)
+
+    return res
+end
+
+-- Difference between 'a' and 'b' storage statistics.
+--
+-- The return value structure is the same as for
+-- helpers.collect_storage_stat().
+function helpers.diff_storage_stat(a, b)
+    local diff = table.deepcopy(a)
+
+    for replicaset_alias, stat_b in pairs(b) do
+        -- Initialize if needed.
+        if diff[replicaset_alias] == nil then
+            diff[replicaset_alias] = {}
+        end
+
+        -- Substract 'b' statistics from 'a'.
+        for key, val in pairs(stat_b) do
+            local old = diff[replicaset_alias][key] or 0
+            diff[replicaset_alias][key] = old - val
+        end
+    end
+
+    return diff
+end
+
 return helpers