diff --git a/idx/memory/memory.go b/idx/memory/memory.go
index a86925d1b5..47cf3b1a74 100755
--- a/idx/memory/memory.go
+++ b/idx/memory/memory.go
@@ -63,7 +63,7 @@ type Tree struct {
 	Items map[string]*Node // key is the full path of the node.
 }
 
-type IdSet map[idx.MetricID]struct{} // set of ids
+type IdSet map[string]struct{} // set of ids
 
 func (ids IdSet) String() string {
 	var res string
@@ -71,7 +71,7 @@ func (ids IdSet) String() string {
 		if len(res) > 0 {
 			res += " "
 		}
-		res += id.String()
+		res += id
 	}
 	return res
 
@@ -80,7 +80,7 @@ func (ids IdSet) String() string {
 type TagValue map[string]IdSet    // value -> set of ids
 type TagIndex map[string]TagValue // key -> list of values
 
-func (t *TagIndex) addTagId(name, value string, id idx.MetricID) {
+func (t *TagIndex) addTagId(name, value string, id string) {
 	ti := *t
 	if _, ok := ti[name]; !ok {
 		ti[name] = make(TagValue)
@@ -91,7 +91,7 @@ func (t *TagIndex) addTagId(name, value string, id idx.MetricID) {
 	ti[name][value][id] = struct{}{}
 }
 
-func (t *TagIndex) delTagId(name, value string, id idx.MetricID) {
+func (t *TagIndex) delTagId(name, value string, id string) {
 	ti := *t
 
 	delete(ti[name][value], id)
@@ -252,15 +252,6 @@ func (m *MemoryIdx) indexTags(def *schema.MetricDefinition) {
 		m.tags[def.OrgId] = tags
 	}
 
-	id, err := idx.NewMetricIDFromString(def.Id)
-	if err != nil {
-		// should never happen because all IDs in the index must have
-		// a valid format
-		invalidId.Inc()
-		log.Error(3, "memory-idx: ID %q has invalid format", def.Id)
-		return
-	}
-
 	for _, tag := range def.Tags {
 		tagSplits := strings.SplitN(tag, "=", 2)
 		if len(tagSplits) < 2 {
@@ -273,9 +264,9 @@ func (m *MemoryIdx) indexTags(def *schema.MetricDefinition) {
 
 		tagName := tagSplits[0]
 		tagValue := tagSplits[1]
-		tags.addTagId(tagName, tagValue, id)
+		tags.addTagId(tagName, tagValue, def.Id)
 	}
-	tags.addTagId("name", def.Name, id)
+	tags.addTagId("name", def.Name, def.Id)
 
 	m.defByTagSet.add(def)
 }
@@ -286,15 +277,6 @@ func (m *MemoryIdx) indexTags(def *schema.MetricDefinition) {
 // unsuccessful, "true" means the indexing was at least partially or completely
 // successful
 func (m *MemoryIdx) deindexTags(tags TagIndex, def *schema.MetricDefinition) bool {
-	id, err := idx.NewMetricIDFromString(def.Id)
-	if err != nil {
-		// should never happen because all IDs in the index must have
-		// a valid format
-		invalidId.Inc()
-		log.Error(3, "memory-idx: ID %q has invalid format", def.Id)
-		return false
-	}
-
 	for _, tag := range def.Tags {
 		tagSplits := strings.SplitN(tag, "=", 2)
 		if len(tagSplits) < 2 {
@@ -307,10 +289,10 @@ func (m *MemoryIdx) deindexTags(tags TagIndex, def *schema.MetricDefinition) boo
 
 		tagName := tagSplits[0]
 		tagValue := tagSplits[1]
-		tags.delTagId(tagName, tagValue, id)
+		tags.delTagId(tagName, tagValue, def.Id)
 	}
 
-	tags.delTagId("name", def.Name, id)
+	tags.delTagId("name", def.Name, def.Id)
 
 	m.defByTagSet.del(def)
 
@@ -515,7 +497,7 @@ func (m *MemoryIdx) TagDetails(orgId int, key, filter string, from int64) (map[s
 		count := uint64(0)
 		if from > 0 {
 			for id := range ids {
-				def, ok := m.defById[id.String()]
+				def, ok := m.defById[id]
 				if !ok {
 					corruptIndex.Inc()
 					log.Error(3, "memory-idx: corrupt. ID %q is in tag index but not in the byId lookup table", id)
@@ -670,7 +652,7 @@ func (m *MemoryIdx) FindTagValues(orgId int, tag, prefix string, expressions []s
 		for id := range ids {
 			var ok bool
 			var def *idx.Archive
-			if def, ok = m.defById[id.String()]; !ok {
+			if def, ok = m.defById[id]; !ok {
 				// should never happen because every ID in the tag index
 				// must be present in the byId lookup table
 				corruptIndex.Inc()
@@ -786,7 +768,7 @@ func (m *MemoryIdx) Tags(orgId int, filter string, from int64) ([]string, error)
 func (m *MemoryIdx) hasOneMetricFrom(tags TagIndex, tag string, from int64) bool {
 	for _, ids := range tags[tag] {
 		for id := range ids {
-			def, ok := m.defById[id.String()]
+			def, ok := m.defById[id]
 			if !ok {
 				corruptIndex.Inc()
 				log.Error(3, "memory-idx: corrupt. ID %q is in tag index but not in the byId lookup table", id)
@@ -820,7 +802,7 @@ func (m *MemoryIdx) FindByTag(orgId int, expressions []string, from int64) ([]id
 	ids := m.idsByTagQuery(orgId, query)
 	res := make([]idx.Node, 0, len(ids))
 	for id := range ids {
-		def, ok := m.defById[id.String()]
+		def, ok := m.defById[id]
 		if !ok {
 			corruptIndex.Inc()
 			log.Error(3, "memory-idx: corrupt. ID %q has been given, but it is not in the byId lookup table", id)
@@ -1071,7 +1053,7 @@ func (m *MemoryIdx) deleteTaggedByIdSet(orgId int, ids IdSet) []idx.Archive {
 
 	deletedDefs := make([]idx.Archive, 0, len(ids))
 	for id := range ids {
-		idStr := id.String()
+		idStr := id
 		def, ok := m.defById[idStr]
 		if !ok {
 			// not necessarily a corruption, the id could have been deleted
@@ -1273,13 +1255,7 @@ DEFS:
 			}
 
 			for def := range defs {
-				id, err := idx.NewMetricIDFromString(def.Id)
-				if err != nil {
-					log.Error(3, "memory-idx: corrupt index. ID format %s seems to be invalid", def.Id)
-					continue
-				}
-
-				toPruneTagged[def.OrgId][id] = struct{}{}
+				toPruneTagged[def.OrgId][def.Id] = struct{}{}
 			}
 		}
 	}
diff --git a/idx/memory/stats.go b/idx/memory/stats.go
index 6c71e9952c..218a8f16f0 100644
--- a/idx/memory/stats.go
+++ b/idx/memory/stats.go
@@ -8,11 +8,6 @@ var (
 	// each time this happens, an error is logged with more details.
 	corruptIndex = stats.NewCounter32("recovered_errors.idx.memory.corrupt-index")
 
-	// metric recovered_errors.idx.memory.invalid-id is how many times
-	// an invalid metric id is encountered.
-	// each time this happens, an error is logged with more details.
-	invalidId = stats.NewCounter32("recovered_errors.idx.memory.invalid-id")
-
 	// metric recovered_errors.idx.memory.invalid-tag is how many times
 	// an invalid tag for a metric is encountered.
 	// each time this happens, an error is logged with more details.
diff --git a/idx/memory/tag_query.go b/idx/memory/tag_query.go
index 8b75d137f6..d33fae57de 100644
--- a/idx/memory/tag_query.go
+++ b/idx/memory/tag_query.go
@@ -333,7 +333,7 @@ func NewTagQuery(expressions []string, from int64) (TagQuery, error) {
 }
 
 // getInitialByEqual generates the initial resultset by executing the given equal expression
-func (q *TagQuery) getInitialByEqual(expr kv, idCh chan idx.MetricID, stopCh chan struct{}) {
+func (q *TagQuery) getInitialByEqual(expr kv, idCh chan string, stopCh chan struct{}) {
 	defer q.wg.Done()
 
 KEYS:
@@ -349,7 +349,7 @@ KEYS:
 }
 
 // getInitialByPrefix generates the initial resultset by executing the given prefix match expression
-func (q *TagQuery) getInitialByPrefix(expr kv, idCh chan idx.MetricID, stopCh chan struct{}) {
+func (q *TagQuery) getInitialByPrefix(expr kv, idCh chan string, stopCh chan struct{}) {
 	defer q.wg.Done()
 
 VALUES:
@@ -371,7 +371,7 @@ VALUES:
 }
 
 // getInitialByMatch generates the initial resultset by executing the given match expression
-func (q *TagQuery) getInitialByMatch(expr kvRe, idCh chan idx.MetricID, stopCh chan struct{}) {
+func (q *TagQuery) getInitialByMatch(expr kvRe, idCh chan string, stopCh chan struct{}) {
 	defer q.wg.Done()
 
 	// shortcut if value == nil.
@@ -412,7 +412,7 @@ VALUES2:
 
 // getInitialByTagPrefix generates the initial resultset by creating a list of
 // metric IDs of which at least one tag starts with the defined prefix
-func (q *TagQuery) getInitialByTagPrefix(idCh chan idx.MetricID, stopCh chan struct{}) {
+func (q *TagQuery) getInitialByTagPrefix(idCh chan string, stopCh chan struct{}) {
 	defer q.wg.Done()
 
 TAGS:
@@ -437,7 +437,7 @@ TAGS:
 
 // getInitialByTagMatch generates the initial resultset by creating a list of
 // metric IDs of which at least one tag matches the defined regex
-func (q *TagQuery) getInitialByTagMatch(idCh chan idx.MetricID, stopCh chan struct{}) {
+func (q *TagQuery) getInitialByTagMatch(idCh chan string, stopCh chan struct{}) {
 	defer q.wg.Done()
 
 TAGS:
@@ -461,8 +461,8 @@ TAGS:
 // getInitialIds asynchronously collects all ID's of the initial result set.  It returns:
 // a channel through which the IDs of the initial result set will be sent
 // a stop channel, which when closed, will cause it to abort the background worker.
-func (q *TagQuery) getInitialIds() (chan idx.MetricID, chan struct{}) {
-	idCh := make(chan idx.MetricID, 1000)
+func (q *TagQuery) getInitialIds() (chan string, chan struct{}) {
+	idCh := make(chan string, 1000)
 	stopCh := make(chan struct{})
 	q.wg.Add(1)
 
@@ -492,7 +492,7 @@ func (q *TagQuery) getInitialIds() (chan idx.MetricID, chan struct{}) {
 // all required tests in order to decide whether this metric should be part
 // of the final result set or not
 // in map/reduce terms this is the reduce function
-func (q *TagQuery) testByAllExpressions(id idx.MetricID, def *idx.Archive, omitTagFilters bool) bool {
+func (q *TagQuery) testByAllExpressions(id string, def *idx.Archive, omitTagFilters bool) bool {
 	if !q.testByFrom(def) {
 		return false
 	}
@@ -695,7 +695,7 @@ func (q *TagQuery) testByTagPrefix(def *idx.Archive) bool {
 }
 
 // testByEqual filters a given metric by the defined "=" expressions
-func (q *TagQuery) testByEqual(id idx.MetricID, exprs []kv, not bool) bool {
+func (q *TagQuery) testByEqual(id string, exprs []kv, not bool) bool {
 	for _, e := range exprs {
 		indexIds := q.index[e.key][e.value]
 
@@ -722,12 +722,12 @@ func (q *TagQuery) testByEqual(id idx.MetricID, exprs []kv, not bool) bool {
 // required tests to decide whether a metric should be part of the final
 // result set or not
 // it returns the final result set via the given resCh parameter
-func (q *TagQuery) filterIdsFromChan(idCh, resCh chan idx.MetricID) {
+func (q *TagQuery) filterIdsFromChan(idCh, resCh chan string) {
 	for id := range idCh {
 		var def *idx.Archive
 		var ok bool
 
-		if def, ok = q.byId[id.String()]; !ok {
+		if def, ok = q.byId[id]; !ok {
 			// should never happen because every ID in the tag index
 			// must be present in the byId lookup table
 			corruptIndex.Inc()
@@ -779,7 +779,7 @@ func (q *TagQuery) Run(index TagIndex, byId map[string]*idx.Archive) IdSet {
 	q.sortByCost()
 
 	idCh, _ := q.getInitialIds()
-	resCh := make(chan idx.MetricID)
+	resCh := make(chan string)
 
 	// start the tag query workers. they'll consume the ids on the idCh and
 	// evaluate for each of them whether it satisfies all the conditions
@@ -836,7 +836,7 @@ func (q *TagQuery) getMaxTagCount() int {
 // according to the criteria associated with this query
 // those that pass all the tests will have their relevant tags extracted, which
 // are then pushed into the given tag channel
-func (q *TagQuery) filterTagsFromChan(idCh chan idx.MetricID, tagCh chan string, stopCh chan struct{}, omitTagFilters bool) {
+func (q *TagQuery) filterTagsFromChan(idCh chan string, tagCh chan string, stopCh chan struct{}, omitTagFilters bool) {
 	// used to prevent that this worker thread will push the same result into
 	// the chan twice
 	resultsCache := make(map[string]struct{})
@@ -846,7 +846,7 @@ IDS:
 		var def *idx.Archive
 		var ok bool
 
-		if def, ok = q.byId[id.String()]; !ok {
+		if def, ok = q.byId[id]; !ok {
 			// should never happen because every ID in the tag index
 			// must be present in the byId lookup table
 			corruptIndex.Inc()
diff --git a/idx/memory/tag_query_test.go b/idx/memory/tag_query_test.go
index 3eff41f88d..fbe7e85775 100644
--- a/idx/memory/tag_query_test.go
+++ b/idx/memory/tag_query_test.go
@@ -11,9 +11,9 @@ import (
 	"gopkg.in/raintank/schema.v1"
 )
 
-var ids []idx.MetricID
+var ids []string
 
-func getTestIDs(t *testing.T) []idx.MetricID {
+func getTestIDs(t *testing.T) []string {
 	if len(ids) > 0 {
 		return ids
 	}
@@ -29,11 +29,7 @@ func getTestIDs(t *testing.T) []idx.MetricID {
 		"1.72345678901234567890123456789012",
 	}
 	for _, idStr := range idStrings {
-		id, err := idx.NewMetricIDFromString(idStr)
-		if err != nil {
-			t.Fatalf("Did not expect an error when converting id string to object: %s", idStr)
-		}
-		ids = append(ids, id)
+		ids = append(ids, idStr)
 	}
 
 	return ids
@@ -41,7 +37,7 @@ func getTestIDs(t *testing.T) []idx.MetricID {
 
 func getTestIndex(t *testing.T) (TagIndex, map[string]*idx.Archive) {
 	type testCase struct {
-		id         idx.MetricID
+		id         string
 		lastUpdate int64
 		tags       []string
 	}
@@ -63,7 +59,7 @@ func getTestIndex(t *testing.T) (TagIndex, map[string]*idx.Archive) {
 	byId := make(map[string]*idx.Archive)
 
 	for i, d := range data {
-		idStr := d.id.String()
+		idStr := d.id
 		byId[idStr] = &idx.Archive{}
 		byId[idStr].Name = fmt.Sprintf("metric%d", i)
 		byId[idStr].Tags = d.tags
@@ -393,12 +389,12 @@ func TestGetByTag(t *testing.T) {
 
 	idString := "1.000000000000000000000000000000%02x"
 	mds := make([]schema.MetricData, 20)
-	ids := make([]idx.MetricID, 20)
+	ids := make([]string, 20)
 	for i := range mds {
-		ids[i], _ = idx.NewMetricIDFromString(fmt.Sprintf(idString, i))
+		ids[i] = fmt.Sprintf(idString, i)
 		mds[i].Metric = fmt.Sprintf("metric.%d", i)
 		mds[i].Name = mds[i].Metric
-		mds[i].Id = ids[i].String()
+		mds[i].Id = ids[i]
 		mds[i].OrgId = 1
 		mds[i].Interval = 1
 		mds[i].Time = 12345
@@ -473,9 +469,9 @@ func TestGetByTag(t *testing.T) {
 
 		resPaths := make([]string, 0, len(res))
 		for id := range res {
-			def, ok := ix.defById[id.String()]
+			def, ok := ix.defById[id]
 			if !ok {
-				t.Fatalf("Tag query returned ID that did not exist in DefByID: %s", id.String())
+				t.Fatalf("Tag query returned ID that did not exist in DefByID: %s", id)
 			}
 			resPaths = append(resPaths, def.NameWithTags())
 		}