Add a collector for pg_buffercache_summary. (#1165)

* Add a collector for pg_buffercache_summary() * Requires PostgreSQL >= 16. --------- Signed-off-by: Peter Nuttall <peter.nuttall@snowflake.com> Co-authored-by: Ben Kochie <superq@gmail.com>
2025-08-06 17:22:43 +03:00 · 2025-06-19 05:33:22 +00:00
parent 94e8399935
commit d8ba628b1e
3 changed files with 217 additions and 0 deletions
--- a/collector/pg_buffercache_summary.go
+++ b/collector/pg_buffercache_summary.go
@@ -0,0 +1,135 @@
+// Copyright 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"
+	"database/sql"
+	"log/slog"
+
+	"github.com/blang/semver/v4"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const buffercacheSummarySubsystem = "buffercache_summary"
+
+func init() {
+	registerCollector(buffercacheSummarySubsystem, defaultDisabled, NewBuffercacheSummaryCollector)
+}
+
+// BuffercacheSummaryCollector collects stats from pg_buffercache: https://www.postgresql.org/docs/current/pgbuffercache.html.
+//
+// It depends on the extension being loaded with
+//
+//	create extension pg_buffercache;
+//
+// It does not take locks, see the PG docs above.
+type BuffercacheSummaryCollector struct {
+	log *slog.Logger
+}
+
+func NewBuffercacheSummaryCollector(config collectorConfig) (Collector, error) {
+	return &BuffercacheSummaryCollector{
+		log: config.logger,
+	}, nil
+}
+
+var (
+	buffersUsedDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "buffers_used"),
+		"Number of used shared buffers",
+		[]string{},
+		prometheus.Labels{},
+	)
+	buffersUnusedDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "buffers_unused"),
+		"Number of unused shared buffers",
+		[]string{},
+		prometheus.Labels{},
+	)
+	buffersDirtyDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "buffers_dirty"),
+		"Number of dirty shared buffers",
+		[]string{},
+		prometheus.Labels{},
+	)
+	buffersPinnedDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "buffers_pinned"),
+		"Number of pinned shared buffers",
+		[]string{},
+		prometheus.Labels{},
+	)
+	usageCountAvgDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "usagecount_avg"),
+		"Average usage count of used shared buffers",
+		[]string{},
+		prometheus.Labels{},
+	)
+
+	buffercacheQuery = `
+		SELECT
+		  buffers_used,
+			buffers_unused,
+			buffers_dirty,
+			buffers_pinned,
+			usagecount_avg
+		FROM
+		  pg_buffercache_summary()
+		`
+)
+
+// Update implements Collector
+// It is called by the Prometheus registry when collecting metrics.
+func (c BuffercacheSummaryCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+	// pg_buffercache_summary is only in v16, and we don't need support for earlier currently.
+	if !instance.version.GE(semver.MustParse("16.0.0")) {
+		return nil
+	}
+	db := instance.getDB()
+	rows, err := db.QueryContext(ctx, buffercacheQuery)
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+
+	var used, unused, dirty, pinned sql.NullInt32
+	var usagecountAvg sql.NullFloat64
+
+	for rows.Next() {
+		if err := rows.Scan(
+			&used,
+			&unused,
+			&dirty,
+			&pinned,
+			&usagecountAvg,
+		); err != nil {
+			return err
+		}
+
+		usagecountAvgMetric := 0.0
+		if usagecountAvg.Valid {
+			usagecountAvgMetric = usagecountAvg.Float64
+		}
+		ch <- prometheus.MustNewConstMetric(
+			usageCountAvgDesc,
+			prometheus.GaugeValue,
+			usagecountAvgMetric)
+		ch <- prometheus.MustNewConstMetric(buffersUsedDesc, prometheus.GaugeValue, Int32(used))
+		ch <- prometheus.MustNewConstMetric(buffersUnusedDesc, prometheus.GaugeValue, Int32(unused))
+		ch <- prometheus.MustNewConstMetric(buffersDirtyDesc, prometheus.GaugeValue, Int32(dirty))
+		ch <- prometheus.MustNewConstMetric(buffersPinnedDesc, prometheus.GaugeValue, Int32(pinned))
+	}
+
+	return rows.Err()
+}