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Add a collector for pg_buffercache_summary. (#1165)
* Add a collector for pg_buffercache_summary() * Requires PostgreSQL >= 16. --------- Signed-off-by: Peter Nuttall <[email protected]> Co-authored-by: Ben Kochie <[email protected]>
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3 files changed

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‎collector/collector.go

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@@ -15,6 +15,7 @@ package collector
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import (
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"context"
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"database/sql"
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"errors"
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"fmt"
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"log/slog"
@@ -228,3 +229,11 @@ var ErrNoData = errors.New("collector returned no data")
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func IsNoDataError(err error) bool {
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return err == ErrNoData
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}
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func Int32(m sql.NullInt32) float64 {
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mM := 0.0
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if m.Valid {
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mM = float64(m.Int32)
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}
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return mM
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}

‎collector/pg_buffercache_summary.go

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@@ -0,0 +1,135 @@
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// Copyright 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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"database/sql"
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"log/slog"
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"github.com/blang/semver/v4"
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"github.com/prometheus/client_golang/prometheus"
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)
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const buffercacheSummarySubsystem = "buffercache_summary"
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func init() {
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registerCollector(buffercacheSummarySubsystem, defaultDisabled, NewBuffercacheSummaryCollector)
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}
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// BuffercacheSummaryCollector collects stats from pg_buffercache: https://www.postgresql.org/docs/current/pgbuffercache.html.
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//
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// It depends on the extension being loaded with
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//
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// create extension pg_buffercache;
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//
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// It does not take locks, see the PG docs above.
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type BuffercacheSummaryCollector struct {
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log *slog.Logger
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}
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func NewBuffercacheSummaryCollector(config collectorConfig) (Collector, error) {
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return &BuffercacheSummaryCollector{
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log: config.logger,
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}, nil
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}
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var (
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buffersUsedDesc = prometheus.NewDesc(
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prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "buffers_used"),
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"Number of used shared buffers",
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[]string{},
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prometheus.Labels{},
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)
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buffersUnusedDesc = prometheus.NewDesc(
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prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "buffers_unused"),
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"Number of unused shared buffers",
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[]string{},
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prometheus.Labels{},
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)
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buffersDirtyDesc = prometheus.NewDesc(
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prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "buffers_dirty"),
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"Number of dirty shared buffers",
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[]string{},
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prometheus.Labels{},
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)
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buffersPinnedDesc = prometheus.NewDesc(
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prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "buffers_pinned"),
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"Number of pinned shared buffers",
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[]string{},
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prometheus.Labels{},
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)
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usageCountAvgDesc = prometheus.NewDesc(
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prometheus.BuildFQName(namespace, buffercacheSummarySubsystem, "usagecount_avg"),
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"Average usage count of used shared buffers",
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[]string{},
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prometheus.Labels{},
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)
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buffercacheQuery = `
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SELECT
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buffers_used,
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buffers_unused,
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buffers_dirty,
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buffers_pinned,
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usagecount_avg
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FROM
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pg_buffercache_summary()
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`
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)
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// Update implements Collector
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// It is called by the Prometheus registry when collecting metrics.
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func (c BuffercacheSummaryCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
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// pg_buffercache_summary is only in v16, and we don't need support for earlier currently.
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if !instance.version.GE(semver.MustParse("16.0.0")) {
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return nil
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}
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db := instance.getDB()
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rows, err := db.QueryContext(ctx, buffercacheQuery)
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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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var used, unused, dirty, pinned sql.NullInt32
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var usagecountAvg sql.NullFloat64
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for rows.Next() {
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if err := rows.Scan(
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&used,
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&unused,
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&dirty,
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&pinned,
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&usagecountAvg,
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); err != nil {
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return err
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}
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usagecountAvgMetric := 0.0
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if usagecountAvg.Valid {
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usagecountAvgMetric = usagecountAvg.Float64
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}
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ch <- prometheus.MustNewConstMetric(
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usageCountAvgDesc,
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prometheus.GaugeValue,
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usagecountAvgMetric)
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ch <- prometheus.MustNewConstMetric(buffersUsedDesc, prometheus.GaugeValue, Int32(used))
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ch <- prometheus.MustNewConstMetric(buffersUnusedDesc, prometheus.GaugeValue, Int32(unused))
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ch <- prometheus.MustNewConstMetric(buffersDirtyDesc, prometheus.GaugeValue, Int32(dirty))
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ch <- prometheus.MustNewConstMetric(buffersPinnedDesc, prometheus.GaugeValue, Int32(pinned))
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}
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return rows.Err()
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}

‎collector/pg_buffercache_summary_test.go

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@@ -0,0 +1,73 @@
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// Copyright 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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"testing"
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"github.com/DATA-DOG/go-sqlmock"
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"github.com/blang/semver/v4"
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"github.com/prometheus/client_golang/prometheus"
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dto "github.com/prometheus/client_model/go"
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"github.com/smartystreets/goconvey/convey"
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)
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func TestBuffercacheSummaryCollector(t *testing.T) {
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db, mock, err := sqlmock.New()
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if err != nil {
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t.Fatalf("Error opening a stub db connection: %s", err)
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}
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defer db.Close()
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inst := &instance{db: db, version: semver.MustParse("16.0.0")}
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columns := []string{
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"buffers_used",
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"buffers_unused",
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"buffers_dirty",
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"buffers_pinned",
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"usagecount_avg"}
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rows := sqlmock.NewRows(columns).AddRow(123, 456, 789, 234, 56.6778)
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mock.ExpectQuery(sanitizeQuery(buffercacheQuery)).WillReturnRows(rows)
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ch := make(chan prometheus.Metric)
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go func() {
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defer close(ch)
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c := BuffercacheSummaryCollector{}
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if err := c.Update(context.Background(), inst, ch); err != nil {
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t.Errorf("Error calling PGStatStatementsCollector.Update: %s", err)
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}
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}()
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expected := []MetricResult{
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{labels: labelMap{}, metricType: dto.MetricType_GAUGE, value: 56.6778},
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{labels: labelMap{}, metricType: dto.MetricType_GAUGE, value: 123},
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{labels: labelMap{}, metricType: dto.MetricType_GAUGE, value: 456},
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{labels: labelMap{}, metricType: dto.MetricType_GAUGE, value: 789},
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{labels: labelMap{}, metricType: dto.MetricType_GAUGE, value: 234},
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}
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convey.Convey("Metrics comparison", t, func() {
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for _, expect := range expected {
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m := readMetric(<-ch)
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convey.So(expect, convey.ShouldResemble, m)
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}
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})
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if err := mock.ExpectationsWereMet(); err != nil {
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t.Errorf("there were unfulfilled exceptions: %s", err)
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}
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}

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