mirror of
https://github.com/prometheus-community/postgres_exporter
synced 2025-04-11 03:31:26 +00:00
c3885e840a
The exported replication lag does not handle all failure modes, and can report 0 for replicas that are out of sync and incapable of recovery. A proper replacement for that metric would require a different approach (see e.g. #1007), but for a lot of folks, simply exporting the age of the last replay can provide a pretty strong signal for something being amiss. I think this solution might be preferable to #977, though the lag metric needs to be fixed or abandoned eventually. Signed-off-by: Conrad Hoffmann <ch@bitfehler.net>
104 lines
2.6 KiB
Go
104 lines
2.6 KiB
Go
// 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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pgReplicationLastReplay = prometheus.NewDesc(
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prometheus.BuildFQName(
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namespace,
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replicationSubsystem,
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"last_replay_seconds",
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),
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"Age of last replay in seconds",
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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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GREATEST (0, EXTRACT(EPOCH FROM (now() - pg_last_xact_replay_timestamp()))) as last_replay`
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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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var replayAge float64
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err := row.Scan(&lag, &isReplica, &replayAge)
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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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ch <- prometheus.MustNewConstMetric(
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pgReplicationLastReplay,
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prometheus.GaugeValue, replayAge,
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)
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return nil
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}
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