Add separate metrics for non-numeric fields

Every report group (PV, VG, LV) had its own info metric where
non-numeric fields like `pv_attr` were reported as a label. Every unique
combination of labels produces a new time series. From
https://prometheus.io/docs/practices/naming/#labels:

> Remember that every unique combination of key-value label pairs
> represents a new time series, which can dramatically increase the
> amount of data stored. Do not use labels to store dimensions with high
> cardinality (many different label values), such as user IDs, email
> addresses, or other unbounded sets of values.

With this change the labels on the info metrics are reduced to names
(e.g. `pv_name` and `lv_full_name`). Everything else is moved to
separate metrics.

A command line flag, enabled by default, retains the labels on the info
metric.

Related to issue #31.

README.md

@@ -37,8 +37,11 @@ directly using [Go][golang] or [GoReleaser][goreleaser].
 ## Example metrics
 
 ```
-lvm_pv_info{pv_fmt="lvm2",pv_name="/dev/sda1",pv_uuid="yc1zVe-…"} 1
-lvm_pv_info{pv_fmt="lvm2",pv_name="/dev/sdb1",pv_uuid="WVIH97-…"} 1
+lvm_pv_info{pv_name="/dev/sda1",pv_uuid="yc1zVe-…"} 1
+lvm_pv_info{pv_name="/dev/sdb1",pv_uuid="WVIH97-…"} 1
+
+lvm_pv_fmt{pv_fmt="lvm2",pv_uuid="yc1zVe-…"} 1
+lvm_pv_fmt{pv_fmt="lvm2",pv_uuid="WVIH97-…"} 1
 
 lvm_pv_free_bytes{pv_uuid="WVIH97-…"} 9.14358272e+08
 lvm_pv_free_bytes{pv_uuid="yc1zVe-…"} 1.040187392e+09

collector_test.go

@@ -73,9 +73,13 @@ func TestCollector(t *testing.T) {
 		{name: "issue30-lockargs"},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
-			for _, enableLegacyInfoLabels := range []bool{false} {
+			for _, enableLegacyInfoLabels := range []bool{false, true} {
 				expectedName := tc.name
 
+				if enableLegacyInfoLabels {
+					expectedName += "-legacy"
+				}
+
 				t.Run(strconv.FormatBool(enableLegacyInfoLabels), func(t *testing.T) {
 					c := newCollector(enableLegacyInfoLabels)
 					c.load = func(ctx context.Context) (*lvmreport.ReportData, error) {

field.go

@@ -8,6 +8,13 @@ func fromNumeric(value string) (float64, error) {
 	return strconv.ParseFloat(value, 64)
 }
 
+type fieldFlag uint
+
+const (
+	// Whether the field should be included as a label on an info metric.
+	asInfoLabel fieldFlag = 1 << iota
+)
+
 type field interface {
 	Name() string
 	MetricName() string
@@ -20,6 +27,8 @@ type textField struct {
 	fieldName string
 	desc      string
 
+	flags fieldFlag
+
 	metricName string
 }
 

groupcollector.go

@@ -27,22 +27,40 @@ func (f *groupField) collect(ch chan<- prometheus.Metric, rawValue string, keyVa
 	return nil
 }
 
+type groupTextField struct {
+	metricDesc *prometheus.Desc
+}
+
+func (f *groupTextField) collect(ch chan<- prometheus.Metric, rawValue string, keyValues []string) error {
+	labels := defaultStringSlicePool.get()
+	defer defaultStringSlicePool.put(labels)
+
+	labels = append(labels, keyValues...)
+	labels = append(labels, rawValue)
+
+	ch <- prometheus.MustNewConstMetric(f.metricDesc, prometheus.GaugeValue, 1, labels...)
+
+	return nil
+}
+
 type groupCollector struct {
 	name lvmreport.GroupName
 
 	infoDesc    *prometheus.Desc
 	unknownDesc *prometheus.Desc
 
-	keyFields     []string
-	textFields    []string
-	numericFields map[string]*groupField
-	knownFields   map[string]struct{}
+	keyFields       []string
+	textFields      map[string]*groupTextField
+	numericFields   map[string]*groupField
+	infoLabelFields []string
+	knownFields     map[string]struct{}
 }
 
 func newGroupCollector(enableLegacyInfoLabels bool, g *group) *groupCollector {
 	c := &groupCollector{
 		name:          g.name,
 		unknownDesc:   prometheus.NewDesc("unknown_field_count", "Fields reported by LVM not recognized by exporter", []string{"group", "details"}, nil),
+		textFields:    map[string]*groupTextField{},
 		numericFields: map[string]*groupField{},
 		knownFields:   map[string]struct{}{},
 	}
@@ -55,15 +73,18 @@ func newGroupCollector(enableLegacyInfoLabels bool, g *group) *groupCollector {
 		keyLabelNames = append(keyLabelNames, f.metricName)
 	}
 
-	infoLabelNames := slices.Clone(keyLabelNames)
-
 	for _, f := range g.textFields {
-		c.textFields = append(c.textFields, f.fieldName)
 		c.knownFields[f.fieldName] = struct{}{}
-		infoLabelNames = append(infoLabelNames, f.metricName)
-	}
 
-	c.infoDesc = prometheus.NewDesc(g.infoMetricName, "", infoLabelNames, nil)
+		if f.flags&asInfoLabel == 0 {
+			textLabelNames := slices.Clone(keyLabelNames)
+			textLabelNames = append(textLabelNames, f.metricName)
+
+			c.textFields[f.fieldName] = &groupTextField{
+				metricDesc: prometheus.NewDesc(f.metricName, f.desc, textLabelNames, nil),
+			}
+		}
+	}
 
 	for _, f := range g.numericFields {
 		info := &groupField{
@@ -77,13 +98,28 @@ func newGroupCollector(enableLegacyInfoLabels bool, g *group) *groupCollector {
 		c.knownFields[f.fieldName] = struct{}{}
 	}
 
+	infoLabelNames := slices.Clone(keyLabelNames)
+
+	for _, f := range g.textFields {
+		if enableLegacyInfoLabels || f.flags&asInfoLabel != 0 {
+			c.infoLabelFields = append(c.infoLabelFields, f.fieldName)
+			infoLabelNames = append(infoLabelNames, f.metricName)
+		}
+	}
+
+	c.infoDesc = prometheus.NewDesc(g.infoMetricName, "", infoLabelNames, nil)
+
 	return c
 }
 
 func (c *groupCollector) describe(ch chan<- *prometheus.Desc) {
 	ch <- c.infoDesc
 	ch <- c.unknownDesc
 
+	for _, info := range c.textFields {
+		ch <- info.metricDesc
+	}
+
 	for _, info := range c.numericFields {
 		ch <- info.metricDesc
 	}
@@ -103,26 +139,31 @@ func (c *groupCollector) collect(ch chan<- prometheus.Metric, data *lvmreport.Re
 
 		infoValues := slices.Clone(keyValues)
 
-		for _, name := range c.textFields {
+		for _, name := range c.infoLabelFields {
 			infoValues = append(infoValues, row[name])
 		}
 
 		ch <- prometheus.MustNewConstMetric(c.infoDesc, prometheus.GaugeValue, 1, infoValues...)
 
 		for fieldName, rawValue := range row {
-			if rawValue == "" {
-				continue
+			var collector interface {
+				collect(chan<- prometheus.Metric, string, []string) error
 			}
 
-			info, ok := c.numericFields[fieldName]
-			if !ok {
+			if info, ok := c.textFields[fieldName]; ok {
+				collector = info
+			} else if rawValue == "" {
+				continue
+			} else if info, ok := c.numericFields[fieldName]; ok {
+				collector = info
+			} else {
 				if _, ok := c.knownFields[fieldName]; !ok {
 					unknown[fieldName] = struct{}{}
 				}
 				continue
 			}
 
-			if err := info.collect(ch, rawValue, keyValues); err != nil {
+			if err := collector.collect(ch, rawValue, keyValues); err != nil {
 				allErrors.Append(fmt.Errorf("field %s: %w", fieldName, err))
 				continue
 			}

lv.go

@@ -97,6 +97,7 @@ var lvGroup = &group{
 		{
 			fieldName:  "lv_full_name",
 			metricName: "lv_full_name",
+			flags:      asInfoLabel,
 			desc:       "Full name of LV including its VG, namely VG/LV",
 		},
 		{
@@ -132,6 +133,7 @@ var lvGroup = &group{
 		{
 			fieldName:  "lv_name",
 			metricName: "lv_name",
+			flags:      asInfoLabel,
 			desc:       "Name; LVs created for internal use are enclosed in brackets",
 		},
 		{

pool.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"sync"
+)
+
+var defaultStringSlicePool = newStringSlicePool()
+
+type stringSlicePool struct {
+	pool sync.Pool
+}
+
+func newStringSlicePool() *stringSlicePool {
+	return &stringSlicePool{
+		pool: sync.Pool{
+			New: func() any {
+				return []string(nil)
+			},
+		},
+	}
+}
+
+// get returns an empty string slice. The caller has ownership of the slice
+// until the slice is put back into the pool.
+func (p *stringSlicePool) get() []string {
+	return p.pool.Get().([]string)[:0]
+}
+
+func (p *stringSlicePool) put(s []string) {
+	// All elements must be accessible.
+	s = s[:cap(s)]
+
+	// Remove references to values.
+	clear(s)
+
+	p.pool.Put(s)
+}

pool_test.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"math/rand/v2"
+	"slices"
+	"strconv"
+	"testing"
+)
+
+func TestStringSlicePool(t *testing.T) {
+	p := newStringSlicePool()
+
+	for range 100 {
+		s := p.get()
+
+		if len(s) > 0 {
+			t.Errorf("get() returned non-empty slice: %q", s)
+		}
+
+		count := rand.IntN(100)
+
+		for i := range count {
+			s = append(s, strconv.Itoa(i))
+		}
+
+		switch rand.IntN(3) {
+		case 1:
+			s = s[:0]
+		case 2:
+			s = s[:count/2]
+		}
+
+		p.put(s)
+
+		if idx := slices.IndexFunc(s[:count], func(value string) bool {
+			return value != ""
+		}); idx != -1 {
+			t.Errorf("Slice was not cleared: %q", s[:count])
+		}
+	}
+}

pv.go

@@ -12,7 +12,12 @@ var pvGroup = &group{
 	textFields: []*textField{
 		{fieldName: "pv_attr", metricName: "pv_attr"},
 		{fieldName: "pv_fmt", metricName: "pv_fmt", desc: "Type of metadata"},
-		{fieldName: "pv_name", metricName: "pv_name", desc: "Name"},
+		{
+			fieldName:  "pv_name",
+			metricName: "pv_name",
+			flags:      asInfoLabel,
+			desc:       "Name",
+		},
 		{fieldName: "pv_tags", metricName: "pv_tags"},
 	},
 	numericFields: []*numericField{

testdata/group-collector-with-error.golden

@@ -2,6 +2,9 @@
 # TYPE lvm_m_count gauge
 lvm_m_count{m_key1="2"} 22
 lvm_m_count{m_key1="3"} 11.5
+# HELP lvm_m_info1 
+# TYPE lvm_m_info1 gauge
+lvm_m_info1{m_info1="info:2",m_key1="2"} 1
 # HELP lvm_test_info 
 # TYPE lvm_test_info gauge
 lvm_test_info{m_info1="",m_key1="1"} 1

testdata/issue29-vdo-online-legacy.golden

@@ -0,0 +1,48 @@
+# HELP lvm_lv_info 
+# TYPE lvm_lv_info gauge
+lvm_lv_info{lv_active="",lv_allocation_policy="",lv_ancestors="",lv_attr="",lv_convert_lv="",lv_convert_lv_uuid="",lv_data_lv="",lv_data_lv_uuid="",lv_descendants="",lv_dm_path="",lv_full_ancestors="",lv_full_descendants="",lv_full_name="",lv_health_status="",lv_host="",lv_kernel_cache_policy="",lv_kernel_cache_settings="",lv_kernel_discards="",lv_kernel_metadata_format="",lv_kernel_read_ahead_bytes="",lv_layout="",lv_lockargs="",lv_metadata_lv="",lv_metadata_lv_uuid="",lv_mirror_log="",lv_mirror_log_uuid="",lv_modules="",lv_move_pv="",lv_move_pv_uuid="",lv_name="[vpool0_vdata]",lv_origin="",lv_origin_uuid="",lv_parent="",lv_path="",lv_permissions="",lv_pool_lv="",lv_pool_lv_uuid="",lv_raid_sync_action="",lv_raidintegritymode="",lv_role="",lv_tags="",lv_uuid="tHnHR1-bjg8-ycJX-eyhR-heEp-L4qs-S510dO",lv_vdo_compression_state="",lv_vdo_index_state="",lv_vdo_operating_mode="",lv_when_full=""} 1
+lvm_lv_info{lv_active="",lv_allocation_policy="",lv_ancestors="",lv_attr="",lv_convert_lv="",lv_convert_lv_uuid="",lv_data_lv="",lv_data_lv_uuid="",lv_descendants="",lv_dm_path="",lv_full_ancestors="",lv_full_descendants="",lv_full_name="",lv_health_status="",lv_host="",lv_kernel_cache_policy="",lv_kernel_cache_settings="",lv_kernel_discards="",lv_kernel_metadata_format="",lv_kernel_read_ahead_bytes="",lv_layout="",lv_lockargs="",lv_metadata_lv="",lv_metadata_lv_uuid="",lv_mirror_log="",lv_mirror_log_uuid="",lv_modules="",lv_move_pv="",lv_move_pv_uuid="",lv_name="lv_data",lv_origin="",lv_origin_uuid="",lv_parent="",lv_path="",lv_permissions="",lv_pool_lv="",lv_pool_lv_uuid="",lv_raid_sync_action="",lv_raidintegritymode="",lv_role="",lv_tags="",lv_uuid="5UyOrx-zG6u-w7cF-G2Ny-HmVd-0lsb-4J6lG2",lv_vdo_compression_state="",lv_vdo_index_state="",lv_vdo_operating_mode="",lv_when_full=""} 1
+lvm_lv_info{lv_active="",lv_allocation_policy="",lv_ancestors="",lv_attr="",lv_convert_lv="",lv_convert_lv_uuid="",lv_data_lv="",lv_data_lv_uuid="",lv_descendants="",lv_dm_path="",lv_full_ancestors="",lv_full_descendants="",lv_full_name="",lv_health_status="",lv_host="",lv_kernel_cache_policy="",lv_kernel_cache_settings="",lv_kernel_discards="",lv_kernel_metadata_format="",lv_kernel_read_ahead_bytes="",lv_layout="",lv_lockargs="",lv_metadata_lv="",lv_metadata_lv_uuid="",lv_mirror_log="",lv_mirror_log_uuid="",lv_modules="",lv_move_pv="",lv_move_pv_uuid="",lv_name="lv_db_backup",lv_origin="",lv_origin_uuid="",lv_parent="",lv_path="",lv_permissions="",lv_pool_lv="",lv_pool_lv_uuid="",lv_raid_sync_action="",lv_raidintegritymode="",lv_role="",lv_tags="",lv_uuid="r7Btja-nL3P-Co38-X2K4-DLWS-LMhT-LajcQa",lv_vdo_compression_state="online",lv_vdo_index_state="online",lv_vdo_operating_mode="normal",lv_when_full=""} 1
+lvm_lv_info{lv_active="",lv_allocation_policy="",lv_ancestors="",lv_attr="",lv_convert_lv="",lv_convert_lv_uuid="",lv_data_lv="",lv_data_lv_uuid="",lv_descendants="",lv_dm_path="",lv_full_ancestors="",lv_full_descendants="",lv_full_name="",lv_health_status="",lv_host="",lv_kernel_cache_policy="",lv_kernel_cache_settings="",lv_kernel_discards="",lv_kernel_metadata_format="",lv_kernel_read_ahead_bytes="",lv_layout="",lv_lockargs="",lv_metadata_lv="",lv_metadata_lv_uuid="",lv_mirror_log="",lv_mirror_log_uuid="",lv_modules="",lv_move_pv="",lv_move_pv_uuid="",lv_name="root",lv_origin="",lv_origin_uuid="",lv_parent="",lv_path="",lv_permissions="",lv_pool_lv="",lv_pool_lv_uuid="",lv_raid_sync_action="",lv_raidintegritymode="",lv_role="",lv_tags="",lv_uuid="cqZnVQ-FUPG-btWz-3fff-cMX5-wViK-8MM3QY",lv_vdo_compression_state="",lv_vdo_index_state="",lv_vdo_operating_mode="",lv_when_full=""} 1
+lvm_lv_info{lv_active="",lv_allocation_policy="",lv_ancestors="",lv_attr="",lv_convert_lv="",lv_convert_lv_uuid="",lv_data_lv="",lv_data_lv_uuid="",lv_descendants="",lv_dm_path="",lv_full_ancestors="",lv_full_descendants="",lv_full_name="",lv_health_status="",lv_host="",lv_kernel_cache_policy="",lv_kernel_cache_settings="",lv_kernel_discards="",lv_kernel_metadata_format="",lv_kernel_read_ahead_bytes="",lv_layout="",lv_lockargs="",lv_metadata_lv="",lv_metadata_lv_uuid="",lv_mirror_log="",lv_mirror_log_uuid="",lv_modules="",lv_move_pv="",lv_move_pv_uuid="",lv_name="swap",lv_origin="",lv_origin_uuid="",lv_parent="",lv_path="",lv_permissions="",lv_pool_lv="",lv_pool_lv_uuid="",lv_raid_sync_action="",lv_raidintegritymode="",lv_role="",lv_tags="",lv_uuid="lGs7Tn-1Fyv-jMHN-aniN-r8qk-duEI-B9Xl9e",lv_vdo_compression_state="",lv_vdo_index_state="",lv_vdo_operating_mode="",lv_when_full=""} 1
+lvm_lv_info{lv_active="",lv_allocation_policy="",lv_ancestors="",lv_attr="",lv_convert_lv="",lv_convert_lv_uuid="",lv_data_lv="",lv_data_lv_uuid="",lv_descendants="",lv_dm_path="",lv_full_ancestors="",lv_full_descendants="",lv_full_name="",lv_health_status="",lv_host="",lv_kernel_cache_policy="",lv_kernel_cache_settings="",lv_kernel_discards="",lv_kernel_metadata_format="",lv_kernel_read_ahead_bytes="",lv_layout="",lv_lockargs="",lv_metadata_lv="",lv_metadata_lv_uuid="",lv_mirror_log="",lv_mirror_log_uuid="",lv_modules="",lv_move_pv="",lv_move_pv_uuid="",lv_name="vpool0",lv_origin="",lv_origin_uuid="",lv_parent="",lv_path="",lv_permissions="",lv_pool_lv="",lv_pool_lv_uuid="",lv_raid_sync_action="",lv_raidintegritymode="",lv_role="",lv_tags="",lv_uuid="dylifl-81AF-n2mG-kFKo-Ntxe-mnNQ-3eB7fF",lv_vdo_compression_state="online",lv_vdo_index_state="online",lv_vdo_operating_mode="normal",lv_when_full=""} 1
+# HELP lvm_lv_vdo_compression_state For vdo pools, whether compression is running
+# TYPE lvm_lv_vdo_compression_state gauge
+lvm_lv_vdo_compression_state{lv_uuid="5UyOrx-zG6u-w7cF-G2Ny-HmVd-0lsb-4J6lG2",lv_vdo_compression_state=""} 1
+lvm_lv_vdo_compression_state{lv_uuid="cqZnVQ-FUPG-btWz-3fff-cMX5-wViK-8MM3QY",lv_vdo_compression_state=""} 1
+lvm_lv_vdo_compression_state{lv_uuid="dylifl-81AF-n2mG-kFKo-Ntxe-mnNQ-3eB7fF",lv_vdo_compression_state="online"} 1
+lvm_lv_vdo_compression_state{lv_uuid="lGs7Tn-1Fyv-jMHN-aniN-r8qk-duEI-B9Xl9e",lv_vdo_compression_state=""} 1
+lvm_lv_vdo_compression_state{lv_uuid="r7Btja-nL3P-Co38-X2K4-DLWS-LMhT-LajcQa",lv_vdo_compression_state="online"} 1
+lvm_lv_vdo_compression_state{lv_uuid="tHnHR1-bjg8-ycJX-eyhR-heEp-L4qs-S510dO",lv_vdo_compression_state=""} 1
+# HELP lvm_lv_vdo_index_state For vdo pools, state of index for deduplication
+# TYPE lvm_lv_vdo_index_state gauge
+lvm_lv_vdo_index_state{lv_uuid="5UyOrx-zG6u-w7cF-G2Ny-HmVd-0lsb-4J6lG2",lv_vdo_index_state=""} 1
+lvm_lv_vdo_index_state{lv_uuid="cqZnVQ-FUPG-btWz-3fff-cMX5-wViK-8MM3QY",lv_vdo_index_state=""} 1
+lvm_lv_vdo_index_state{lv_uuid="dylifl-81AF-n2mG-kFKo-Ntxe-mnNQ-3eB7fF",lv_vdo_index_state="online"} 1
+lvm_lv_vdo_index_state{lv_uuid="lGs7Tn-1Fyv-jMHN-aniN-r8qk-duEI-B9Xl9e",lv_vdo_index_state=""} 1
+lvm_lv_vdo_index_state{lv_uuid="r7Btja-nL3P-Co38-X2K4-DLWS-LMhT-LajcQa",lv_vdo_index_state="online"} 1
+lvm_lv_vdo_index_state{lv_uuid="tHnHR1-bjg8-ycJX-eyhR-heEp-L4qs-S510dO",lv_vdo_index_state=""} 1
+# HELP lvm_lv_vdo_operating_mode For vdo pools, its current operating mode
+# TYPE lvm_lv_vdo_operating_mode gauge
+lvm_lv_vdo_operating_mode{lv_uuid="5UyOrx-zG6u-w7cF-G2Ny-HmVd-0lsb-4J6lG2",lv_vdo_operating_mode=""} 1
+lvm_lv_vdo_operating_mode{lv_uuid="cqZnVQ-FUPG-btWz-3fff-cMX5-wViK-8MM3QY",lv_vdo_operating_mode=""} 1
+lvm_lv_vdo_operating_mode{lv_uuid="dylifl-81AF-n2mG-kFKo-Ntxe-mnNQ-3eB7fF",lv_vdo_operating_mode="normal"} 1
+lvm_lv_vdo_operating_mode{lv_uuid="lGs7Tn-1Fyv-jMHN-aniN-r8qk-duEI-B9Xl9e",lv_vdo_operating_mode=""} 1
+lvm_lv_vdo_operating_mode{lv_uuid="r7Btja-nL3P-Co38-X2K4-DLWS-LMhT-LajcQa",lv_vdo_operating_mode="normal"} 1
+lvm_lv_vdo_operating_mode{lv_uuid="tHnHR1-bjg8-ycJX-eyhR-heEp-L4qs-S510dO",lv_vdo_operating_mode=""} 1
+# HELP lvm_lv_vdo_saving_percent For vdo pools, percentage of saved space
+# TYPE lvm_lv_vdo_saving_percent gauge
+lvm_lv_vdo_saving_percent{lv_uuid="dylifl-81AF-n2mG-kFKo-Ntxe-mnNQ-3eB7fF"} 55.37
+lvm_lv_vdo_saving_percent{lv_uuid="r7Btja-nL3P-Co38-X2K4-DLWS-LMhT-LajcQa"} 55.37
+# HELP lvm_lv_vdo_used_size_bytes For vdo pools, currently used space
+# TYPE lvm_lv_vdo_used_size_bytes gauge
+lvm_lv_vdo_used_size_bytes{lv_uuid="dylifl-81AF-n2mG-kFKo-Ntxe-mnNQ-3eB7fF"} 2.78899963904e+12
+lvm_lv_vdo_used_size_bytes{lv_uuid="r7Btja-nL3P-Co38-X2K4-DLWS-LMhT-LajcQa"} 2.78899963904e+12
+# HELP lvm_unknown_field_count Fields reported by LVM not recognized by exporter
+# TYPE lvm_unknown_field_count gauge
+lvm_unknown_field_count{details="",group="lv"} 0
+lvm_unknown_field_count{details="",group="pv"} 0
+lvm_unknown_field_count{details="",group="vg"} 0
+# HELP lvm_up Whether scrape was successful
+# TYPE lvm_up gauge
+lvm_up{status=""} 1