Add special handling of "buffer_page_io" subsystem

For information_schema.innodb_metrics we can split out labels based on
the type of buffer page IO operation in the "buffer_page_io" subsystem.
* Simplify scrapeInnodbMetrics() by casting value to float64.
* Test for broken metric output from MySQL.
* Supress log messages in the test.

collector/info_schema_innodb_metrics.go

@@ -4,8 +4,10 @@ package collector
 
 import (
 	"database/sql"
+	"regexp"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/common/log"
 )
 
 const infoSchemaInnodbMetricsQuery = `
@@ -16,6 +18,23 @@ const infoSchemaInnodbMetricsQuery = `
 		  WHERE status = 'enabled'
 		`
 
+// Metrics descriptors.
+var (
+	infoSchemaBufferPageReadTotalDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, informationSchema, "innodb_metrics_buffer_page_read_total"),
+		"Total number of buffer pages read total.",
+		[]string{"type"}, nil,
+	)
+	infoSchemaBufferPageWrittenTotalDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, informationSchema, "innodb_metrics_buffer_page_written_total"),
+		"Total number of buffer pages written total.",
+		[]string{"type"}, nil,
+	)
+)
+
+// Regexp for matching metric aggregations.
+var bufferPageRE = regexp.MustCompile(`^buffer_page_(read|written)_(.*)$`)
+
 // ScrapeInnodbMetrics collects from `information_schema.innodb_metrics`.
 func ScrapeInnodbMetrics(db *sql.DB, ch chan<- prometheus.Metric) error {
 	innodbMetricsRows, err := db.Query(infoSchemaInnodbMetricsQuery)
@@ -26,7 +45,7 @@ func ScrapeInnodbMetrics(db *sql.DB, ch chan<- prometheus.Metric) error {
 
 	var (
 		name, subsystem, metricType, comment string
-		value                                int64
+		value                                float64
 	)
 
 	for innodbMetricsRows.Next() {
@@ -35,6 +54,25 @@ func ScrapeInnodbMetrics(db *sql.DB, ch chan<- prometheus.Metric) error {
 		); err != nil {
 			return err
 		}
+		// Special handling of the "buffer_page_io" subsystem.
+		if subsystem == "buffer_page_io" {
+			match := bufferPageRE.FindStringSubmatch(name)
+			if len(match) != 3 {
+				log.Warnln("innodb_metrics subsystem buffer_page_io returned an invalid name:", name)
+				continue
+			}
+			switch match[1] {
+			case "read":
+				ch <- prometheus.MustNewConstMetric(
+					infoSchemaBufferPageReadTotalDesc, prometheus.CounterValue, value, match[2],
+				)
+			case "written":
+				ch <- prometheus.MustNewConstMetric(
+					infoSchemaBufferPageWrittenTotalDesc, prometheus.CounterValue, value, match[2],
+				)
+			}
+			continue
+		}
 		metricName := "innodb_metrics_" + subsystem + "_" + name
 		// MySQL returns counters named two different ways. "counter" and "status_counter"
 		// value >= 0 is necessary due to upstream bugs: http://bugs.mysql.com/bug.php?id=75966
@@ -46,7 +84,7 @@ func ScrapeInnodbMetrics(db *sql.DB, ch chan<- prometheus.Metric) error {
 			ch <- prometheus.MustNewConstMetric(
 				description,
 				prometheus.CounterValue,
-				float64(value),
+				value,
 			)
 		} else {
 			description := prometheus.NewDesc(
@@ -56,7 +94,7 @@ func ScrapeInnodbMetrics(db *sql.DB, ch chan<- prometheus.Metric) error {
 			ch <- prometheus.MustNewConstMetric(
 				description,
 				prometheus.GaugeValue,
-				float64(value),
+				value,
 			)
 		}
 	}

collector/info_schema_innodb_metrics_test.go

@@ -0,0 +1,62 @@
+package collector
+
+import (
+	"flag"
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/smartystreets/goconvey/convey"
+	"gopkg.in/DATA-DOG/go-sqlmock.v1"
+)
+
+func TestScrapeInnodbMetrics(t *testing.T) {
+	// Suppress a log messages
+	err := flag.Set("log.level", "fatal")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("error opening a stub database connection: %s", err)
+	}
+	defer db.Close()
+
+	columns := []string{"name", "subsystem", "type", "comment", "count"}
+	rows := sqlmock.NewRows(columns).
+		AddRow("lock_timeouts", "lock", "counter", "Number of lock timeouts", 0).
+		AddRow("buffer_pool_reads", "buffer", "status_counter", "Number of reads directly from disk (innodb_buffer_pool_reads)", 1).
+		AddRow("buffer_pool_size", "server", "value", "Server buffer pool size (all buffer pools) in bytes", 2).
+		AddRow("buffer_page_read_system_page", "buffer_page_io", "counter", "Number of System Pages read", 3).
+		AddRow("buffer_page_written_undo_log", "buffer_page_io", "counter", "Number of Undo Log Pages written", 4).
+		AddRow("NOPE", "buffer_page_io", "counter", "An invalid buffer_page_io metric", 5)
+	mock.ExpectQuery(sanitizeQuery(infoSchemaInnodbMetricsQuery)).WillReturnRows(rows)
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		if err = ScrapeInnodbMetrics(db, ch); err != nil {
+			t.Errorf("error calling function on test: %s", err)
+		}
+		close(ch)
+	}()
+
+	metricExpected := []MetricResult{
+		{labels: labelMap{}, value: 0, metricType: dto.MetricType_COUNTER},
+		{labels: labelMap{}, value: 1, metricType: dto.MetricType_COUNTER},
+		{labels: labelMap{}, value: 2, metricType: dto.MetricType_GAUGE},
+		{labels: labelMap{"type": "system_page"}, value: 3, metricType: dto.MetricType_COUNTER},
+		{labels: labelMap{"type": "undo_log"}, value: 4, metricType: dto.MetricType_COUNTER},
+	}
+	convey.Convey("Metrics comparison", t, func() {
+		for _, expect := range metricExpected {
+			got := readMetric(<-ch)
+			convey.So(got, convey.ShouldResemble, expect)
+		}
+	})
+
+	// Ensure all SQL queries were executed
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("there were unfulfilled expections: %s", err)
+	}
+}