diff --git a/compact.go b/compact.go
index 7d8174f0d3..a3bc7d17a3 100644
--- a/compact.go
+++ b/compact.go
@@ -17,7 +17,6 @@ import (
 	"math/rand"
 	"os"
 	"path/filepath"
-	"runtime"
 	"sort"
 	"time"
 
@@ -365,10 +364,6 @@ func (c *LeveledCompactor) write(dest string, meta *BlockMeta, blocks ...BlockRe
 		}
 		c.metrics.ran.Inc()
 		c.metrics.duration.Observe(time.Since(t).Seconds())
-
-		// We might have done quite a few allocs. Enforce a GC so they do not accumulate
-		// with subsequent compactions or head GCs.
-		runtime.GC()
 	}(time.Now())
 
 	dir := filepath.Join(dest, meta.ULID.String())
@@ -570,14 +565,6 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 			return errors.Wrap(err, "write postings")
 		}
 	}
-	// Write a postings list containing all series.
-	all := make([]uint64, i)
-	for i := range all {
-		all[i] = uint64(i)
-	}
-	if err := indexw.WritePostings("", "", newListPostings(all)); err != nil {
-		return errors.Wrap(err, "write 'all' postings")
-	}
 
 	return nil
 }
diff --git a/db.go b/db.go
index ad034d8b02..c9745cfc6f 100644
--- a/db.go
+++ b/db.go
@@ -21,6 +21,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"runtime"
 	"sort"
 	"strconv"
 	"sync"
@@ -349,9 +350,12 @@ func (db *DB) compact() (changes bool, err error) {
 		}
 		changes = true
 
+		runtime.GC()
+
 		if err := db.reload(); err != nil {
 			return changes, errors.Wrap(err, "reload blocks")
 		}
+		runtime.GC()
 	}
 
 	// Check for compactions of multiple blocks.
@@ -380,10 +384,12 @@ func (db *DB) compact() (changes bool, err error) {
 				return changes, errors.Wrap(err, "delete compacted block")
 			}
 		}
+		runtime.GC()
 
 		if err := db.reload(); err != nil {
 			return changes, errors.Wrap(err, "reload blocks")
 		}
+		runtime.GC()
 	}
 
 	return changes, nil
diff --git a/encoding_helpers.go b/encoding_helpers.go
index 9aa4ba4097..17c3ff0811 100644
--- a/encoding_helpers.go
+++ b/encoding_helpers.go
@@ -77,6 +77,22 @@ func (d *decbuf) uvarint32() uint32 { return uint32(d.uvarint64()) }
 func (d *decbuf) be32int() int      { return int(d.be32()) }
 func (d *decbuf) be64int64() int64  { return int64(d.be64()) }
 
+// uvarintTempStr decodes like uvarintStr but the returned string is
+// not safe to use if the underyling buffer changes.
+func (d *decbuf) uvarintTempStr() string {
+	l := d.uvarint64()
+	if d.e != nil {
+		return ""
+	}
+	if len(d.b) < int(l) {
+		d.e = errInvalidSize
+		return ""
+	}
+	s := yoloString(d.b[:l])
+	d.b = d.b[l:]
+	return s
+}
+
 func (d *decbuf) uvarintStr() string {
 	l := d.uvarint64()
 	if d.e != nil {
diff --git a/head.go b/head.go
index b2d6e9842d..ea7b63f8a6 100644
--- a/head.go
+++ b/head.go
@@ -15,7 +15,6 @@ package tsdb
 
 import (
 	"math"
-	"runtime"
 	"sort"
 	"sync"
 	"sync/atomic"
@@ -515,8 +514,6 @@ Outer:
 
 // gc removes data before the minimum timestmap from the head.
 func (h *Head) gc() {
-	defer runtime.GC()
-
 	// Only data strictly lower than this timestamp must be deleted.
 	mint := h.MinTime()
 
diff --git a/index.go b/index.go
index ddc2c4f52a..e65f3fec15 100644
--- a/index.go
+++ b/index.go
@@ -335,10 +335,6 @@ func (w *indexWriter) AddSymbols(sym map[string]struct{}) error {
 
 	for _, s := range symbols {
 		w.symbols[s] = uint32(w.pos) + headerSize + uint32(w.buf2.len())
-
-		// NOTE: len(s) gives the number of runes, not the number of bytes.
-		// Therefore the read-back length for strings with unicode characters will
-		// be off when not using putUvarintStr.
 		w.buf2.putUvarintStr(s)
 	}
 
@@ -636,7 +632,7 @@ func (r *indexReader) readOffsetTable(off uint64) (map[string]uint32, error) {
 		keys := make([]string, 0, keyCount)
 
 		for i := 0; i < keyCount; i++ {
-			keys = append(keys, d2.uvarintStr())
+			keys = append(keys, d2.uvarintTempStr())
 		}
 		res[strings.Join(keys, sep)] = uint32(d2.uvarint())
 
@@ -673,7 +669,7 @@ func (r *indexReader) section(o uint32) (byte, []byte, error) {
 func (r *indexReader) lookupSymbol(o uint32) (string, error) {
 	d := r.decbufAt(int(o))
 
-	s := d.uvarintStr()
+	s := d.uvarintTempStr()
 	if d.err() != nil {
 		return "", errors.Wrapf(d.err(), "read symbol at %d", o)
 	}
@@ -688,7 +684,7 @@ func (r *indexReader) Symbols() (map[string]struct{}, error) {
 	sym := make(map[string]struct{}, count)
 
 	for ; count > 0; count-- {
-		s := d2.uvarintStr()
+		s := d2.uvarintTempStr()
 		sym[s] = struct{}{}
 	}
 
diff --git a/wal_test.go b/wal_test.go
index a3177ee6ac..f36b22e90e 100644
--- a/wal_test.go
+++ b/wal_test.go
@@ -399,6 +399,9 @@ func TestWALRestoreCorrupted(t *testing.T) {
 
 			require.NoError(t, w.Close())
 
+			// cut() truncates and fsyncs the first segment async. If it happens after
+			// the corruption we apply below, the corruption will be overwritten again.
+			// Fire and forget a sync to avoid flakyness.
 			w.files[0].Sync()
 			// Corrupt the second entry in the first file.
 			// After re-opening we must be able to read the first entry