From 1b569e36d411329ff6263dd4f097707bb8eabf21 Mon Sep 17 00:00:00 2001
From: Felix Yuan <felix.yuan@reddit.com>
Date: Wed, 28 Jun 2023 10:52:00 -0700
Subject: [PATCH] Oldest Blocked collector and test

Signed-off-by: Felix Yuan <felix.yuan@reddit.com>
---
 collector/pg_oldest_blocked.go      | 83 +++++++++++++++++++++++++++++
 collector/pg_oldest_blocked_test.go | 61 +++++++++++++++++++++
 2 files changed, 144 insertions(+)
 create mode 100644 collector/pg_oldest_blocked.go
 create mode 100644 collector/pg_oldest_blocked_test.go

diff --git a/collector/pg_oldest_blocked.go b/collector/pg_oldest_blocked.go
new file mode 100644
index 00000000..6bbf52ed
--- /dev/null
+++ b/collector/pg_oldest_blocked.go
@@ -0,0 +1,83 @@
+// Copyright 2023 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package collector
+
+import (
+	"context"
+
+	"github.com/go-kit/log"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const oldestBlockedSubsystem = "oldest_blocked"
+
+func init() {
+	registerCollector(oldestBlockedSubsystem, defaultDisabled, NewPGOldestBlockedCollector)
+}
+
+type PGOldestBlockedCollector struct {
+	log log.Logger
+}
+
+func NewPGOldestBlockedCollector(config collectorConfig) (Collector, error) {
+	return &PGOldestBlockedCollector{log: config.logger}, nil
+}
+
+var (
+	oldestBlockedAgeSeconds = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, oldestBlockedSubsystem, "age_seconds"),
+		"Largest number of seconds any transaction is currently waiting on a lock",
+		[]string{},
+		prometheus.Labels{},
+	)
+
+	oldestBlockedQuery = `
+	SELECT
+		coalesce(extract('epoch' from max(clock_timestamp() - state_change)), 0) age_seconds
+	FROM
+		pg_catalog.pg_stat_activity
+	WHERE
+		wait_event_type = 'Lock'
+	 	AND state='active'
+	`
+)
+
+func (PGOldestBlockedCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+	db := instance.getDB()
+	rows, err := db.QueryContext(ctx,
+		oldestBlockedQuery)
+
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var ageSeconds float64
+
+		if err := rows.Scan(&ageSeconds); err != nil {
+			return err
+		}
+
+		ch <- prometheus.MustNewConstMetric(
+			oldestBlockedAgeSeconds,
+			prometheus.GaugeValue,
+			ageSeconds,
+		)
+	}
+	if err := rows.Err(); err != nil {
+		return err
+	}
+	return nil
+}
diff --git a/collector/pg_oldest_blocked_test.go b/collector/pg_oldest_blocked_test.go
new file mode 100644
index 00000000..9aac3762
--- /dev/null
+++ b/collector/pg_oldest_blocked_test.go
@@ -0,0 +1,61 @@
+// Copyright 2023 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package collector
+
+import (
+	"context"
+	"testing"
+
+	"github.com/DATA-DOG/go-sqlmock"
+	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/smartystreets/goconvey/convey"
+)
+
+func TestPgOldestBlockedCollector(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub db connection: %s", err)
+	}
+	defer db.Close()
+	inst := &instance{db: db}
+	columns := []string{
+		"age_seconds",
+	}
+	rows := sqlmock.NewRows(columns).
+		AddRow(100000)
+
+	mock.ExpectQuery(sanitizeQuery(oldestBlockedQuery)).WillReturnRows(rows)
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := PGOldestBlockedCollector{}
+
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling PGOldestBlockedCollector.Update: %s", err)
+		}
+	}()
+	expected := []MetricResult{
+		{labels: labelMap{}, value: 100000, metricType: dto.MetricType_GAUGE},
+	}
+	convey.Convey("Metrics comparison", t, func() {
+		for _, expect := range expected {
+			m := readMetric(<-ch)
+			convey.So(expect, convey.ShouldResemble, m)
+		}
+	})
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("there were unfulfilled exceptions: %s", err)
+	}
+}