drop unused TxBitmap

TxBitmap was a workaround for performance problems with doing
individual-bit operations directly on RBF, used only in the
large-writes path of importValue. With importValue no longer
using that path, ever, there are zero remaining users of TxBitmap,
and the test for it no longer exercises it.

Solution: Remove it.

fragment_internal_test.go

@@ -6091,40 +6091,3 @@ func TestBitmapGrowth(t *testing.T) {
 			deltaSize, deltaOpN)
 	}
 }
-
-func TestTxBitmap(t *testing.T) {
-	f, _, tx := mustOpenFragment(t, "i", "f", viewBSIGroupPrefix+"foo", 0, "")
-	defer f.Clean(t)
-	f.MaxOpN = 8
-	cols := []uint64{1, 2, 3, 4, 5, 6, 65537, 131073}
-	vals := []int64{4, 4, 4, 4, 4, 4, 4, 4}
-	zeros := []int64{0, 0, 0, 0, 0, 0, 0, 0}
-	err := f.importValue(tx, cols, vals, 7, false)
-	if err != nil {
-		t.Fatalf("importing values: %v", err)
-	}
-	expected := []uint64{1, (4 * ShardWidth) + 1}
-	var got []uint64
-	_ = tx.ForEach("i", "f", viewBSIGroupPrefix+"foo", 0, func(i uint64) error {
-		got = append(got, i)
-		return nil
-	})
-	t.Logf("initial: %d", got)
-	err = f.importValue(tx, cols[1:], zeros[1:], 7, true)
-	if err != nil {
-		t.Fatalf("clearing values: %v", err)
-	}
-	got = got[:0]
-	_ = tx.ForEach("i", "f", viewBSIGroupPrefix+"foo", 0, func(i uint64) error {
-		got = append(got, i)
-		return nil
-	})
-	if len(got) != len(expected) {
-		t.Fatalf("bitmap clear unsuccessful: expected %d, got %d", expected, got)
-	}
-	for i := range expected {
-		if expected[i] != got[i] {
-			t.Fatalf("bitmap clear unsuccessful: expected %d, got %d", expected, got)
-		}
-	}
-}

tx.go

@@ -247,83 +247,6 @@ func (rr *RawRoaringData) Iterator() (roaring.RoaringIterator, error) {
 	return roaring.NewRoaringIterator(rr.data)
 }
 
-// TxBitmap represents a bitmap that acts as a cache in front of a transaction.
-// Updates to the bitmap first pull in containers as needed and update them
-// in memory. The changes can be flushed in bulk using Flush().
-type TxBitmap struct {
-	b     *roaring.Bitmap
-	tx    Tx
-	index string
-	field string
-	view  string
-	shard uint64
-	// Container keys we've already snagged containers for, even if
-	// those containers have since been deleted by remove ops.
-	seen map[uint64]struct{}
-}
-
-func NewTxBitmap(tx Tx, index, field, view string, shard uint64) *TxBitmap {
-	return &TxBitmap{
-		b:     roaring.NewBitmap(),
-		tx:    tx,
-		index: index,
-		field: field,
-		view:  view,
-		shard: shard,
-		seen:  make(map[uint64]struct{}),
-	}
-}
-
-func (b *TxBitmap) Add(a ...uint64) (changed bool, err error) {
-	if err := b.ensureContainers(a...); err != nil {
-		return false, err
-	}
-	return b.b.Add(a...)
-}
-
-func (b *TxBitmap) Remove(a ...uint64) (changed bool, err error) {
-	if err := b.ensureContainers(a...); err != nil {
-		return false, err
-	}
-	return b.b.Remove(a...)
-}
-
-// ensureContainers pulls containers in from the transaction, if needed.
-func (b *TxBitmap) ensureContainers(a ...uint64) error {
-	for _, v := range a {
-		key := highbits(v)
-		if _, ok := b.seen[key]; ok {
-			continue
-		}
-		c, err := b.tx.Container(b.index, b.field, b.view, b.shard, key)
-		if err != nil {
-			return err
-		}
-		b.seen[key] = struct{}{}
-		b.b.Containers.Put(key, c)
-	}
-	return nil
-}
-
-// Flush writes all containers in the bitmap back to the transaction.
-func (b *TxBitmap) Flush() error {
-	for it, _ := b.b.Containers.Iterator(0); it.Next(); {
-		key, c := it.Value()
-		if err := b.tx.PutContainer(b.index, b.field, b.view, b.shard, key, c); err != nil {
-			return err
-		}
-		delete(b.seen, key)
-	}
-	// remove containers we have seen but no longer have, because that means
-	// we deleted everything from them.
-	for key := range b.seen {
-		if err := b.tx.RemoveContainer(b.index, b.field, b.view, b.shard, key); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
 // GenericApplyFilter implements ApplyFilter in terms of tx.ContainerIterator,
 // as a convenience if a Tx backend hasn't implemented this new function yet.
 func GenericApplyFilter(tx Tx, index, field, view string, shard uint64, ckey uint64, filter roaring.BitmapFilter) (err error) {