【MySQL】——mysql exporter源码分析

灰太狼 2022-10-17 05:29 242阅读 0赞

### 一、前言 ###

最近在做mysql innodb cluster的监控，发现mysql innodb cluster的集群状态没有对应的指标能采集到，索性看一波源码，魔改一把吧。源码链接奉上: [https://github.com/prometheus/mysqld\_exporter][https_github.com_prometheus_mysqld_exporter]

### 二、源码阅读 ###

1、入口(main函数)

可以看到，MySQL Exporter提供了两个URL供访问，一个是 `/`，用于打印一些基本的信息，另一个就是用于收集metrics的 `/metrics` 链接。

func main() {
    	// Generate ON/OFF flags for all scrapers.
    	scraperFlags := map[collector.Scraper]*bool{}
    	for scraper, enabledByDefault := range scrapers {
    		defaultOn := "false"
    		if enabledByDefault {
    			defaultOn = "true"
    		}
    
    		f := kingpin.Flag(
    			"collect."+scraper.Name(),
    			scraper.Help(),
    		).Default(defaultOn).Bool()
    
    		scraperFlags[scraper] = f
    	}
    
    	// Parse flags.
    	promlogConfig := &promlog.Config{}
    	flag.AddFlags(kingpin.CommandLine, promlogConfig)
    	kingpin.Version(version.Print("mysqld_exporter"))
    	kingpin.HelpFlag.Short('h')
    	kingpin.Parse()
    	logger := promlog.New(promlogConfig)
    
    	// landingPage contains the HTML served at '/'.
    	// TODO: Make this nicer and more informative.
    	var landingPage = []byte(`<html>
    <head><title>MySQLd exporter</title></head>
    <body>
    <h1>MySQLd exporter</h1>
    <p><a href='` + *metricPath + `'>Metrics</a></p>
    </body>
    </html>
    `)
    
    	level.Info(logger).Log("msg", "Starting msqyld_exporter", "version", version.Info())
    	level.Info(logger).Log("msg", "Build context", version.BuildContext())
    
    	dsn = os.Getenv("DATA_SOURCE_NAME")
    	if len(dsn) == 0 {
    		var err error
    		if dsn, err = parseMycnf(*configMycnf); err != nil {
    			level.Info(logger).Log("msg", "Error parsing my.cnf", "file", *configMycnf, "err", err)
    			os.Exit(1)
    		}
    	}
    
    	// Register only scrapers enabled by flag.
    	enabledScrapers := []collector.Scraper{}
    	for scraper, enabled := range scraperFlags {
    		if *enabled {
    			level.Info(logger).Log("msg", "Scraper enabled", "scraper", scraper.Name())
    			enabledScrapers = append(enabledScrapers, scraper)
    		}
    	}
    	handlerFunc := newHandler(collector.NewMetrics(), enabledScrapers, logger)
    	http.Handle(*metricPath, promhttp.InstrumentMetricHandler(prometheus.DefaultRegisterer, handlerFunc))
    	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
    		w.Write(landingPage)
    	})
    
    	level.Info(logger).Log("msg", "Listening on address", "address", *listenAddress)
    	srv := &http.Server{Addr: *listenAddress}
    	if err := web.ListenAndServe(srv, *webConfig, logger); err != nil {
    		level.Error(logger).Log("msg", "Error starting HTTP server", "err", err)
    		os.Exit(1)
    	}
    }

2. `metrics` 对应的handler

我们进去看看 `/metrics` 对应的handler，它是由 `newHandler` 生成的：

func newHandler(metrics collector.Metrics, scrapers []collector.Scraper, logger log.Logger) http.HandlerFunc {
    	return func(w http.ResponseWriter, r *http.Request) {
    		filteredScrapers := scrapers
    		params := r.URL.Query()["collect[]"]
    		// Use request context for cancellation when connection gets closed.
    		ctx := r.Context()
    		// If a timeout is configured via the Prometheus header, add it to the context.
    		if v := r.Header.Get("X-Prometheus-Scrape-Timeout-Seconds"); v != "" {
    			timeoutSeconds, err := strconv.ParseFloat(v, 64)
    			if err != nil {
    				level.Error(logger).Log("msg", "Failed to parse timeout from Prometheus header", "err", err)
    			} else {
    				if *timeoutOffset >= timeoutSeconds {
    					// Ignore timeout offset if it doesn't leave time to scrape.
    					level.Error(logger).Log("msg", "Timeout offset should be lower than prometheus scrape timeout", "offset", *timeoutOffset, "prometheus_scrape_timeout", timeoutSeconds)
    				} else {
    					// Subtract timeout offset from timeout.
    					timeoutSeconds -= *timeoutOffset
    				}
    				// Create new timeout context with request context as parent.
    				var cancel context.CancelFunc
    				ctx, cancel = context.WithTimeout(ctx, time.Duration(timeoutSeconds*float64(time.Second)))
    				defer cancel()
    				// Overwrite request with timeout context.
    				r = r.WithContext(ctx)
    			}
    		}
    		level.Debug(logger).Log("msg", "collect[] params", "params", strings.Join(params, ","))
    
    		// Check if we have some "collect[]" query parameters.
    		if len(params) > 0 {
    			filters := make(map[string]bool)
    			for _, param := range params {
    				filters[param] = true
    			}
    
    			filteredScrapers = nil
    			for _, scraper := range scrapers {
    				if filters[scraper.Name()] {
    					filteredScrapers = append(filteredScrapers, scraper)
    				}
    			}
    		}
    
    		registry := prometheus.NewRegistry()
    		registry.MustRegister(collector.New(ctx, dsn, metrics, filteredScrapers, logger))
    
    		gatherers := prometheus.Gatherers{
    			prometheus.DefaultGatherer,
    			registry,
    		}
    		// Delegate http serving to Prometheus client library, which will call collector.Collect.
    		h := promhttp.HandlerFor(gatherers, promhttp.HandlerOpts{})
    		h.ServeHTTP(w, r)
    	}
    }

3. 接口

而关键就在于 `registry.MustRegister` 要求给的参数是符合 `Collector` 接口的实现，也就是说，每次需要收集信息的时候，就会调用 `Collector` 接口的 `Collect` 方法：

type Collector interface {
    	Describe(chan<- *Desc)
    	Collect(chan<- Metric)
    }

我们不难发现，收集器并发收集所有指标，每个具体指标都会实现 `Scraper` 这个接口：

// Scraper is minimal interface that let's you add new prometheus metrics to mysqld_exporter.
    type Scraper interface {
    	// Name of the Scraper. Should be unique.
    	Name() string
    
    	// Help describes the role of the Scraper.
    	// Example: "Collect from SHOW ENGINE INNODB STATUS"
    	Help() string
    
    	// Version of MySQL from which scraper is available.
    	Version() float64
    
    	// Scrape collects data from database connection and sends it over channel as prometheus metric.
    	Scrape(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error
    }

那就简单了，我们如果想要实现一个指标的采集只要实现该接口就行，而具体的指标，就在 `Scrape` 这个接口里，从数据库里查出来，并且利用 各种方式把需要的数据提取出来，例如文本解析，正则等等。我们来看一个简单的收集器：

slave\_status.go

// Copyright 2018 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.
    
    // Scrape `SHOW SLAVE STATUS`.
    
    package collector
    
    import (
    	"context"
    	"database/sql"
    	"fmt"
    	"strings"
    
    	"github.com/go-kit/kit/log"
    	"github.com/prometheus/client_golang/prometheus"
    )
    
    const (
    	// Subsystem.
    	slaveStatus = "slave_status"
    )
    
    var slaveStatusQueries = [2]string{"SHOW ALL SLAVES STATUS", "SHOW SLAVE STATUS"}
    var slaveStatusQuerySuffixes = [3]string{" NONBLOCKING", " NOLOCK", ""}
    
    func columnIndex(slaveCols []string, colName string) int {
    	for idx := range slaveCols {
    		if slaveCols[idx] == colName {
    			return idx
    		}
    	}
    	return -1
    }
    
    func columnValue(scanArgs []interface{}, slaveCols []string, colName string) string {
    	var columnIndex = columnIndex(slaveCols, colName)
    	if columnIndex == -1 {
    		return ""
    	}
    	return string(*scanArgs[columnIndex].(*sql.RawBytes))
    }
    
    // ScrapeSlaveStatus collects from `SHOW SLAVE STATUS`.
    type ScrapeSlaveStatus struct{}
    
    // Name of the Scraper. Should be unique.
    func (ScrapeSlaveStatus) Name() string {
    	return slaveStatus
    }
    
    // Help describes the role of the Scraper.
    func (ScrapeSlaveStatus) Help() string {
    	return "Collect from SHOW SLAVE STATUS"
    }
    
    // Version of MySQL from which scraper is available.
    func (ScrapeSlaveStatus) Version() float64 {
    	return 5.1
    }
    
    // Scrape collects data from database connection and sends it over channel as prometheus metric.
    func (ScrapeSlaveStatus) Scrape(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric, logger log.Logger) error {
    	var (
    		slaveStatusRows *sql.Rows
    		err             error
    	)
    	// Try the both syntax for MySQL/Percona and MariaDB
    	for _, query := range slaveStatusQueries {
    		slaveStatusRows, err = db.QueryContext(ctx, query)
    		if err != nil { // MySQL/Percona
    			// Leverage lock-free SHOW SLAVE STATUS by guessing the right suffix
    			for _, suffix := range slaveStatusQuerySuffixes {
    				slaveStatusRows, err = db.QueryContext(ctx, fmt.Sprint(query, suffix))
    				if err == nil {
    					break
    				}
    			}
    		} else { // MariaDB
    			break
    		}
    	}
    	if err != nil {
    		return err
    	}
    	defer slaveStatusRows.Close()
    
    	slaveCols, err := slaveStatusRows.Columns()
    	if err != nil {
    		return err
    	}
    
    	for slaveStatusRows.Next() {
    		// As the number of columns varies with mysqld versions,
    		// and sql.Scan requires []interface{}, we need to create a
    		// slice of pointers to the elements of slaveData.
    		scanArgs := make([]interface{}, len(slaveCols))
    		for i := range scanArgs {
    			scanArgs[i] = &sql.RawBytes{}
    		}
    
    		if err := slaveStatusRows.Scan(scanArgs...); err != nil {
    			return err
    		}
    
    		masterUUID := columnValue(scanArgs, slaveCols, "Master_UUID")
    		masterHost := columnValue(scanArgs, slaveCols, "Master_Host")
    		channelName := columnValue(scanArgs, slaveCols, "Channel_Name")       // MySQL & Percona
    		connectionName := columnValue(scanArgs, slaveCols, "Connection_name") // MariaDB
    
    		for i, col := range slaveCols {
    			if value, ok := parseStatus(*scanArgs[i].(*sql.RawBytes)); ok { // Silently skip unparsable values.
    				ch <- prometheus.MustNewConstMetric(
    					prometheus.NewDesc(
    						prometheus.BuildFQName(namespace, slaveStatus, strings.ToLower(col)),
    						"Generic metric from SHOW SLAVE STATUS.",
    						[]string{"master_host", "master_uuid", "channel_name", "connection_name"},
    						nil,
    					),
    					prometheus.UntypedValue,
    					value,
    					masterHost, masterUUID, channelName, connectionName,
    				)
    			}
    		}
    	}
    	return nil
    }
    
    // check interface
    var _ Scraper = ScrapeSlaveStatus{}

4. 采集的集合

通过上边的代码，我们已经知道了，mysql exporter采集指标的方式就是一个个实现接口就行，我们可以很方便扩展。我们可以用集合来表示监控参数的范围。首先exporter中利用scrapers常量记录了一个默认的采集范围集合A。

var scrapers = map[collector.Scraper]bool{
    	collector.ScrapeGlobalStatus{}:                        true,
    	collector.ScrapeGlobalVariables{}:                     true,
    	collector.ScrapeSlaveStatus{}:                         true,
    	collector.ScrapeProcesslist{}:                         false,
    	collector.ScrapeUser{}:                                false,
    	collector.ScrapeTableSchema{}:                         false,
    	collector.ScrapeInfoSchemaInnodbTablespaces{}:         false,
    	collector.ScrapeInnodbMetrics{}:                       false,
    	collector.ScrapeAutoIncrementColumns{}:                false,
    	collector.ScrapeBinlogSize{}:                          false,
    	collector.ScrapePerfTableIOWaits{}:                    false,
    	collector.ScrapePerfIndexIOWaits{}:                    false,
    	collector.ScrapePerfTableLockWaits{}:                  false,
    	collector.ScrapePerfEventsStatements{}:                false,
    	collector.ScrapePerfEventsStatementsSum{}:             false,
    	collector.ScrapePerfEventsWaits{}:                     false,
    	collector.ScrapePerfFileEvents{}:                      false,
    	collector.ScrapePerfFileInstances{}:                   false,
    	collector.ScrapePerfMemoryEvents{}:                    false,
    	collector.ScrapePerfReplicationGroupMembers{}:         false,
    	collector.ScrapePerfReplicationGroupMemberStats{}:     false,
    	collector.ScrapePerfReplicationApplierStatsByWorker{}: false,
    	collector.ScrapeUserStat{}:                            false,
    	collector.ScrapeClientStat{}:                          false,
    	collector.ScrapeTableStat{}:                           false,
    	collector.ScrapeSchemaStat{}:                          false,
    	collector.ScrapeInnodbCmp{}:                           true,
    	collector.ScrapeInnodbCmpMem{}:                        true,
    	collector.ScrapeQueryResponseTime{}:                   true,
    	collector.ScrapeEngineTokudbStatus{}:                  false,
    	collector.ScrapeEngineInnodbStatus{}:                  false,
    	collector.ScrapeHeartbeat{}:                           false,
    	collector.ScrapeSlaveHosts{}:                          false,
    	collector.ScrapeReplicaHost{}:                         false,
    }

exporter也允许在exporter启动的时候，通过设置启动参数来设置采集范围B。当集合B不存在时，集合A生效；当集合B存在时，集合B生效，集合A失效。Prometheus在采集exporter的数据时，可以携带一个collect\[\]参数设定采集范围C。当集合C不存在时，Prometheus最终的采集范围是A或者B（取决于哪个集合生效）；当集合C存在时，Prometheus最终的采集范围时C和A或者B（取决于哪个集合生效）的交集。

### 三、参考资料 ###

1.[https://jiajunhuang.com/articles/2018\_12\_16-prometheus\_mysqld\_exporter.md.html][https_jiajunhuang.com_articles_2018_12_16-prometheus_mysqld_exporter.md.html]

2. [https://github.com/prometheus/mysqld\_exporter][https_github.com_prometheus_mysqld_exporter]

[https_github.com_prometheus_mysqld_exporter]: https://github.com/prometheus/mysqld_exporter
[https_jiajunhuang.com_articles_2018_12_16-prometheus_mysqld_exporter.md.html]: https://jiajunhuang.com/articles/2018_12_16-prometheus_mysqld_exporter.md.html