Add schema reload counter to stats

Add counter of schema reloads in calls to module statistics. Schema
reloads are counted over all spaces and stored in top level, like
`space_not_found` counter.

```
crud.stats().schema_reloads
---
- 2
...

```

In metrics, they are stored in `tnt_crud_schema_reloads` counter.

Follows up #224

Author: DifferentialOrange

README.md

@@ -638,6 +638,7 @@ crud.stats()
           count: 4
           time: 0.000004
   space_not_found: 0
+  schema_reloads: 0
 ...
 crud.stats('my_space')
 ---
@@ -658,7 +659,9 @@ field will be empty. If no operations has been called for a
 space, it will not be represented. Operations called for
 spaces not found both on storages and in statistics registry
 (including cases when crud can't verify space existence)
-will increment `space_not_found` counter.
+will increment `space_not_found` counter. Operation calls
+that reloaded a schema will increment `schema_reloads`
+counter.
 
 Possible statistics operation labels are
 `insert` (for `insert` and `insert_object` calls),
@@ -678,7 +681,8 @@ otherwise `latency` is total average.
 In [`metrics`](https://www.tarantool.io/en/doc/latest/book/monitoring/)
 registry statistics are stored as `tnt_crud_stats` metrics
 with `operation`, `status` and `name` labels. Collector
-`tnt_crud_space_not_found` stores count of calls to unknown spaces.
+`tnt_crud_space_not_found` stores count of calls to unknown spaces,
+`tnt_crud_schema_reloads` stores count of schema reloads in calls.
 ```
 metrics:collect()
 ---

crud/common/fiber_context.lua

@@ -0,0 +1,22 @@
+local fiber = require('fiber')
+
+local fiber_context = {}
+
+function fiber_context.init_section(section)
+    local storage = fiber.self().storage
+    if storage[section] == nil then
+        storage[section] = {}
+    end
+
+    return storage[section]
+end
+
+function fiber_context.get_section(section)
+    return fiber.self().storage[section]
+end
+
+function fiber_context.drop_section(section)
+    fiber.self().storage[section] = nil
+end
+
+return fiber_context

crud/common/schema.lua

@@ -9,6 +9,7 @@ local ReloadSchemaError = errors.new_class('ReloadSchemaError', {capture_stack =
 
 local const = require('crud.common.const')
 local dev_checks = require('crud.common.dev_checks')
+local fiber_context = require('crud.common.fiber_context')
 
 local schema = {}
 
@@ -103,6 +104,13 @@ function schema.wrap_func_reload(func, ...)
         end
     end
 
+    local context_stats = fiber_context.init_section('router_stats')
+    if context_stats.schema_reloads == nil then
+        context_stats.schema_reloads = i
+    else
+        context_stats.schema_reloads = context_stats.schema_reloads + i
+    end
+
     return res, err
 end
 

crud/common/utils.lua

@@ -1,6 +1,5 @@
 local errors = require('errors')
 local ffi = require('ffi')
-local fiber = require('fiber')
 local vshard = require('vshard')
 local fun = require('fun')
 
@@ -614,21 +613,4 @@ end
 -- Do nothing.
 function utils.pass() end
 
-function utils.init_context_section(section)
-    local storage = fiber.self().storage
-    if storage[section] == nil then
-        storage[section] = {}
-    end
-
-    return storage[section]
-end
-
-function utils.get_context_section(section)
-    return fiber.self().storage[section]
-end
-
-function utils.drop_context_section(section)
-    fiber.self().storage[section] = nil
-end
-
 return utils

crud/select.lua

@@ -1,5 +1,6 @@
 local errors = require('errors')
 
+local fiber_context = require('crud.common.fiber_context')
 local utils = require('crud.common.utils')
 local select_executor = require('crud.select.executor')
 local select_filters = require('crud.select.filters')
@@ -76,8 +77,8 @@ local function select_on_storage(space_name, index_id, conditions, opts)
         cursor = make_cursor(tuples)
     end
 
-    cursor.stats = utils.get_context_section('storage_stats')
-    utils.drop_context_section('storage_stats')
+    cursor.stats = fiber_context.get_section('storage_stats')
+    fiber_context.drop_section('storage_stats')
 
     -- getting tuples with user defined fields (if `fields` option is specified)
     -- and fields that are needed for comparison on router (primary key + scan key)

crud/select/compat/select.lua

@@ -2,6 +2,7 @@ local checks = require('checks')
 local errors = require('errors')
 local vshard = require('vshard')
 
+local fiber_context = require('crud.common.fiber_context')
 local utils = require('crud.common.utils')
 local sharding = require('crud.common.sharding')
 local dev_checks = require('crud.common.dev_checks')
@@ -113,7 +114,7 @@ local function build_select_iterator(space_name, user_conditions, opts)
             return nil, err, true
         end
     else
-        local context_stats = utils.init_context_section('router_stats')
+        local context_stats = fiber_context.init_section('router_stats')
         context_stats.map_reduces = 1
     end
 

crud/select/compat/select_old.lua

@@ -4,6 +4,7 @@ local vshard = require('vshard')
 local fun = require('fun')
 
 local call = require('crud.common.call')
+local fiber_context = require('crud.common.fiber_context')
 local utils = require('crud.common.utils')
 local sharding = require('crud.common.sharding')
 local dev_checks = require('crud.common.dev_checks')
@@ -148,7 +149,7 @@ local function build_select_iterator(space_name, user_conditions, opts)
             return nil, err, true
         end
     else
-        local context_stats = utils.init_context_section('router_stats')
+        local context_stats = fiber_context.init_section('router_stats')
         context_stats.map_reduces = 1
     end
 

crud/select/executor.lua

@@ -1,6 +1,7 @@
 local errors = require('errors')
 
 local dev_checks = require('crud.common.dev_checks')
+local fiber_context = require('crud.common.fiber_context')
 local select_comparators = require('crud.compare.comparators')
 local compat = require('crud.common.compat')
 local has_keydef = compat.exists('tuple.keydef', 'key_def')
@@ -68,7 +69,7 @@ function executor.execute(space, index, filter_func, opts)
 
     opts = opts or {}
 
-    local stats = utils.init_context_section('storage_stats')
+    local stats = fiber_context.init_section('storage_stats')
     stats.tuples_lookup = 0
     stats.tuples_fetched = 0
 

crud/stats/local_registry.lua

@@ -31,6 +31,7 @@ function registry.init(opts)
     internal.registry = {}
     internal.registry.spaces = {}
     internal.registry.space_not_found = 0
+    internal.registry.schema_reloads = 0
 
     return true
 end
@@ -188,4 +189,21 @@ function registry.observe_map_reduces(count, space_name)
     return true
 end
 
+--- Increase statistics of schema reloads
+--
+-- @function observe_schema_reloads
+--
+-- @tparam number count
+--  Schema reloads performed.
+--
+-- @treturn boolean Returns true.
+--
+function registry.observe_schema_reloads(count)
+    dev_checks('number')
+
+    internal.registry.schema_reloads = internal.registry.schema_reloads + count
+
+    return true
+end
+
 return registry

crud/stats/metrics_registry.lua

@@ -20,6 +20,9 @@ local metric_name = {
     -- Counter collector for spaces not found.
     space_not_found = 'tnt_crud_space_not_found',
 
+    -- Counter collector for schema reloads.
+    schema_reloads = 'tnt_crud_schema_reloads',
+
     -- Counter collectors for select/pairs details.
     details = {
         tuples_fetched = 'tnt_crud_tuples_fetched',
@@ -110,6 +113,10 @@ function registry.init(opts)
         metric_name.space_not_found,
         'Spaces not found during CRUD calls')
 
+    internal.registry[metric_name.schema_reloads] = metrics.counter(
+        metric_name.schema_reloads,
+        'Schema reloads performed in operation calls')
+
     internal.registry[metric_name.details.tuples_fetched] = metrics.counter(
         metric_name.details.tuples_fetched,
         'Tuples fetched from CRUD storages during select/pairs')
@@ -210,6 +217,7 @@ function registry.get(space_name)
     local stats = {
         spaces = {},
         space_not_found = 0,
+        schema_reloads = 0,
     }
 
     -- Fill operation basic statistics values.
@@ -264,9 +272,14 @@ function registry.get(space_name)
         return stats.spaces[space_name] or {}
     end
 
-    local _, obs = next(internal.registry[metric_name.space_not_found]:collect())
-    if obs ~= nil then
-        stats.space_not_found = obs.value
+    local _, not_found_obs = next(internal.registry[metric_name.space_not_found]:collect())
+    if not_found_obs ~= nil then
+        stats.space_not_found = not_found_obs.value
+    end
+
+    local _, reload_obs = next(internal.registry[metric_name.schema_reloads]:collect())
+    if reload_obs ~= nil then
+        stats.schema_reloads = reload_obs.value
     end
 
     return stats
@@ -396,6 +409,23 @@ function registry.observe_map_reduces(count, space_name)
     return true
 end
 
+--- Increase statistics of schema reloads
+--
+-- @function observe_schema_reloads
+--
+-- @tparam number count
+--  Schema reloads performed.
+--
+-- @treturn boolean Returns true.
+--
+function registry.observe_schema_reloads(count)
+    dev_checks('number')
+
+    internal.registry[metric_name.schema_reloads]:inc(count)
+
+    return true
+end
+
 -- Workaround for https://github.com/tarantool/metrics/issues/334 .
 -- This workaround does not prevent observations reset between role reloads,
 -- but it fixes collector unlink from registry. Without this workaround,