pangolin_exporter

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// Copyright 2023 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package collector
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import (
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	"context"
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	"github.com/prometheus/client_golang/prometheus"
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)
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const replicationSubsystem = "replication"
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func init() {
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	registerCollector(replicationSubsystem, defaultEnabled, NewPGReplicationCollector)
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}
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type PGReplicationCollector struct {
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}
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func NewPGReplicationCollector(collectorConfig) (Collector, error) {
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	return &PGReplicationCollector{}, nil
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}
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var (
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	pgReplicationLag = prometheus.NewDesc(
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		prometheus.BuildFQName(
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			namespace,
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			replicationSubsystem,
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			"lag_seconds",
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		),
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		"Replication lag behind master in seconds",
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		[]string{}, nil,
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	)
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	pgReplicationIsReplica = prometheus.NewDesc(
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		prometheus.BuildFQName(
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			namespace,
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			replicationSubsystem,
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			"is_replica",
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		),
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		"Indicates if the server is a replica",
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		[]string{}, nil,
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	)
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	pgReplicationQuery = `SELECT
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	CASE
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		WHEN NOT pg_is_in_recovery() THEN 0
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                WHEN pg_last_wal_receive_lsn () = pg_last_wal_replay_lsn () THEN 0
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		ELSE GREATEST (0, EXTRACT(EPOCH FROM (now() - pg_last_xact_replay_timestamp())))
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	END AS lag,
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	CASE
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		WHEN pg_is_in_recovery() THEN 1
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		ELSE 0
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	END as is_replica`
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)
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func (c *PGReplicationCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
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	db := instance.getDB()
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	row := db.QueryRowContext(ctx,
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		pgReplicationQuery,
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	)
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	var lag float64
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	var isReplica int64
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	err := row.Scan(&lag, &isReplica)
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	if err != nil {
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		return err
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	}
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	ch <- prometheus.MustNewConstMetric(
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		pgReplicationLag,
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		prometheus.GaugeValue, lag,
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	)
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	ch <- prometheus.MustNewConstMetric(
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		pgReplicationIsReplica,
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		prometheus.GaugeValue, float64(isReplica),
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	)
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	return nil
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}
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