schema: add schema needs upgrade metric

Metric checks whether schema needs an upgrade.
Value 1 means upgrade required, 0 means schema up-to-date.

Closes TNTP-4904

Author: Satbek

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - `tnt_memory` metric.
 - `tnt_memory_virt` metric.
+- `tnt_schema_needs_upgrade` metric.
 
 ### Changed
 

doc/monitoring/metrics_reference.rst

@@ -23,7 +23,23 @@ General instance information:
         *   -   ``tnt_read_only``
             -   Indicates if the instance is in read-only mode (``1`` if true, ``0`` if false)
 
-..  _metrics-reference-memory_general:
+..  _metrics-reference-schema:
+
+Schema
+------
+
+Schema state metrics.
+
+..  container:: table
+
+    ..  list-table::
+        :widths: 25 75
+        :header-rows: 0
+
+        *   -   ``tnt_schema_needs_upgrade``
+            -   Indicates if the instance schema requires an upgrade (``1`` when upgrade is needed, ``0`` when schema is up to date)
+
+..  _metrics-reference-instance:
 
 Instance metrics
 ----------------
@@ -45,7 +61,7 @@ These metrics can be used to monitor instance CPU and RAM usage.
         *   -   ``tnt_memory_virt``
             -   Virtual memory size in bytes used by Tarantool instance (available on Linux).
 
-.. _metrics-reference-instance:
+..  _metrics-reference-memory_general:
 
 Memory general
 --------------

metrics/tarantool.lua

@@ -27,6 +27,7 @@ local default_metrics = {
     event_loop          = require('metrics.tarantool.event_loop'),
     config              = require('metrics.tarantool.config'),
     cpu_extended        = require('metrics.psutils.cpu'),
+    schema              = require('metrics.tarantool.schema')
 }
 
 local all_metrics_map = {}

metrics/tarantool/schema.lua

@@ -0,0 +1,32 @@
+local utils = require('metrics.utils')
+-- luacheck: globals box
+
+local collectors_list = {}
+
+local metric_name = 'schema_needs_upgrade'
+
+local needs_upgrade_status = {
+    [true] = 1,
+    [false] = 0,
+}
+
+local function update_schema_metrics()
+    if not utils.box_is_configured() then
+        return
+    end
+
+    local ok, needs_upgrade = pcall(box.schema_needs_upgrade)
+    if not ok then
+        ok, needs_upgrade = pcall(box.internal.schema_needs_upgrade)
+    end
+
+    if ok then
+        collectors_list[metric_name] = utils.set_gauge(metric_name, 'Schema needs upgrade',
+            needs_upgrade_status[needs_upgrade], nil, nil, {default = true})
+    end
+end
+
+return {
+    update = update_schema_metrics,
+    list = collectors_list,
+}

test/tarantool/schema_test.lua

@@ -0,0 +1,25 @@
+require('strict').on()
+
+local t = require('luatest')
+local g = t.group()
+
+local utils = require('test.utils')
+
+g.before_all(utils.create_server)
+
+g.after_all(utils.drop_server)
+
+g.test_needs_upgrade = function(cg)
+    cg.server:exec(function()
+        local metrics = require('metrics')
+        local schema = require('metrics.tarantool.schema')
+        local utils = require('test.utils') -- luacheck: ignore 431
+
+        metrics.enable_default_metrics()
+        schema.update()
+        local default_metrics = metrics.collect()
+        local schema_needs_upgrade_metric = utils.find_metric('tnt_schema_needs_upgrade', default_metrics)
+        t.assert(schema_needs_upgrade_metric)
+        t.assert_type(schema_needs_upgrade_metric[1].value, 'number')
+    end)
+end