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/blang/semver/v4"
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	"github.com/go-kit/log"
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	"github.com/go-kit/log/level"
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	"github.com/prometheus/client_golang/prometheus"
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)
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const xlogLocationSubsystem = "xlog_location"
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func init() {
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	registerCollector(xlogLocationSubsystem, defaultDisabled, NewPGXlogLocationCollector)
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}
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type PGXlogLocationCollector struct {
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	log log.Logger
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}
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func NewPGXlogLocationCollector(config collectorConfig) (Collector, error) {
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	return &PGXlogLocationCollector{log: config.logger}, nil
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}
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var (
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	xlogLocationBytes = prometheus.NewDesc(
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		prometheus.BuildFQName(namespace, xlogLocationSubsystem, "bytes"),
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		"Postgres LSN (log sequence number) being generated on primary or replayed on replica (truncated to low 52 bits)",
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		[]string{},
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		prometheus.Labels{},
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	)
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	xlogLocationQuery = `
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	SELECT CASE
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		WHEN pg_is_in_recovery() THEN (pg_last_xlog_replay_location() - '0/0') % (2^52)::bigint
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		ELSE (pg_current_xlog_location() - '0/0') % (2^52)::bigint
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	END AS bytes
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	`
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)
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func (c PGXlogLocationCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
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	db := instance.getDB()
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	// xlog was renmaed to WAL in PostgreSQL 10
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	// https://wiki.postgresql.org/wiki/New_in_postgres_10#Renaming_of_.22xlog.22_to_.22wal.22_Globally_.28and_location.2Flsn.29
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	after10 := instance.version.Compare(semver.MustParse("10.0.0"))
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	if after10 >= 0 {
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		level.Warn(c.log).Log("msg", "xlog_location collector is not available on PostgreSQL >= 10.0.0, skipping")
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		return nil
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	}
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	rows, err := db.QueryContext(ctx,
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		xlogLocationQuery)
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	if err != nil {
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		return err
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	}
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	defer rows.Close()
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	for rows.Next() {
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		var bytes float64
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		if err := rows.Scan(&bytes); err != nil {
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			return err
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		}
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		ch <- prometheus.MustNewConstMetric(
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			xlogLocationBytes,
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			prometheus.GaugeValue,
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			bytes,
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		)
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	}
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	if err := rows.Err(); err != nil {
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		return err
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	}
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	return nil
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}
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