base: add NoFilterPolicy

This is cleaner than special-casing `nil` and will allow
differentiating between an unset value and a value that is
specifically set to `NoFilterPolicy`.

Author: RaduBerinde

cmd/pebble/db.go

@@ -105,7 +105,7 @@ func newPebbleDB(dir string) DB {
 		}
 		l.EnsureDefaults()
 	}
-	opts.Levels[6].FilterPolicy = nil
+	opts.Levels[6].FilterPolicy = pebble.NoFilterPolicy
 	opts.FlushSplitBytes = opts.Levels[0].TargetFileSize
 
 	opts.EnsureDefaults()

cmd/pebble/replay.go

@@ -300,7 +300,7 @@ func (c *replayConfig) parseHooks() *pebble.ParseHooks {
 		NewFilterPolicy: func(name string) (pebble.FilterPolicy, error) {
 			switch name {
 			case "none":
-				return nil, nil
+				return base.NoFilterPolicy, nil
 			case "rocksdb.BuiltinBloomFilter":
 				return bloom.FilterPolicy(10), nil
 			default:

internal/base/options.go

@@ -65,6 +65,15 @@ type FilterPolicy interface {
 	NewWriter(ftype FilterType) FilterWriter
 }
 
+// NoFilterPolicy implements the "none" filter policy.
+var NoFilterPolicy FilterPolicy = noFilter{}
+
+type noFilter struct{}
+
+func (noFilter) Name() string                                         { return "none" }
+func (noFilter) MayContain(ftype FilterType, filter, key []byte) bool { return true }
+func (noFilter) NewWriter(ftype FilterType) FilterWriter              { panic("not implemented") }
+
 // BlockPropertyFilter is used in an Iterator to filter sstables and blocks
 // within the sstable. It should not maintain any per-sstable state, and must
 // be thread-safe.

metamorphic/options.go

@@ -792,7 +792,7 @@ func RandomOptions(
 	opts.Filters = nil
 	switch rng.IntN(3) {
 	case 0:
-		lopts.FilterPolicy = nil
+		lopts.FilterPolicy = pebble.NoFilterPolicy
 	case 1:
 		lopts.FilterPolicy = bloom.FilterPolicy(10)
 	default:
@@ -1030,7 +1030,7 @@ func (t *testingFilterPolicy) Name() string {
 func filterPolicyFromName(name string) (pebble.FilterPolicy, error) {
 	switch name {
 	case "none":
-		return nil, nil
+		return base.NoFilterPolicy, nil
 	case "rocksdb.BuiltinBloomFilter":
 		return bloom.FilterPolicy(10), nil
 	}

options.go

@@ -69,6 +69,8 @@ type FilterWriter = base.FilterWriter
 // FilterPolicy exports the base.FilterPolicy type.
 type FilterPolicy = base.FilterPolicy
 
+var NoFilterPolicy = base.NoFilterPolicy
+
 // KeySchema exports the colblk.KeySchema type.
 type KeySchema = colblk.KeySchema
 
@@ -421,7 +423,7 @@ type LevelOptions struct {
 	// One such implementation is bloom.FilterPolicy(10) from the pebble/bloom
 	// package.
 	//
-	// The default value means to use no filter.
+	// The default value is NoFilterPolicy.
 	FilterPolicy FilterPolicy
 
 	// FilterType defines whether an existing filter policy is applied at a
@@ -464,6 +466,9 @@ func (o *LevelOptions) EnsureDefaults() {
 	if o.Compression == nil {
 		o.Compression = func() Compression { return DefaultCompression }
 	}
+	if o.FilterPolicy == nil {
+		o.FilterPolicy = NoFilterPolicy
+	}
 	if o.IndexBlockSize <= 0 {
 		o.IndexBlockSize = o.BlockSize
 	}
@@ -1454,7 +1459,7 @@ func (o *Options) AddEventListener(l EventListener) {
 func (o *Options) initMaps() {
 	for i := range o.Levels {
 		l := &o.Levels[i]
-		if l.FilterPolicy != nil {
+		if l.FilterPolicy != NoFilterPolicy {
 			if o.Filters == nil {
 				o.Filters = make(map[string]FilterPolicy)
 			}
@@ -1488,13 +1493,6 @@ func (o *Options) Clone() *Options {
 	return n
 }
 
-func filterPolicyName(p FilterPolicy) string {
-	if p == nil {
-		return "none"
-	}
-	return p.Name()
-}
-
 func (o *Options) String() string {
 	var buf bytes.Buffer
 
@@ -1612,7 +1610,7 @@ func (o *Options) String() string {
 		fmt.Fprintf(&buf, "  block_size=%d\n", l.BlockSize)
 		fmt.Fprintf(&buf, "  block_size_threshold=%d\n", l.BlockSizeThreshold)
 		fmt.Fprintf(&buf, "  compression=%s\n", resolveDefaultCompression(l.Compression()))
-		fmt.Fprintf(&buf, "  filter_policy=%s\n", filterPolicyName(l.FilterPolicy))
+		fmt.Fprintf(&buf, "  filter_policy=%s\n", l.FilterPolicy.Name())
 		fmt.Fprintf(&buf, "  filter_type=%s\n", l.FilterType)
 		fmt.Fprintf(&buf, "  index_block_size=%d\n", l.IndexBlockSize)
 		fmt.Fprintf(&buf, "  target_file_size=%d\n", l.TargetFileSize)
@@ -2103,6 +2101,8 @@ func (o *Options) Parse(s string, hooks *ParseHooks) error {
 			case "filter_policy":
 				if hooks != nil && hooks.NewFilterPolicy != nil {
 					l.FilterPolicy, err = hooks.NewFilterPolicy(value)
+				} else {
+					l.FilterPolicy = NoFilterPolicy
 				}
 			case "filter_type":
 				switch value {

sstable/colblk_writer.go

@@ -150,7 +150,7 @@ func newColumnarWriter(
 			block.MakeFlushGovernor(o.BlockSize, o.BlockSizeThreshold, o.SizeClassAwareThreshold, o.AllocatorSizeClasses),
 			w.opts.Compression, w.opts.Checksum, func(compressedSize int) {})
 	}
-	if o.FilterPolicy != nil {
+	if o.FilterPolicy != base.NoFilterPolicy {
 		switch o.FilterType {
 		case TableFilter:
 			w.filterBlock = newTableFilterWriter(o.FilterPolicy)

sstable/copier.go

@@ -8,6 +8,7 @@ import (
 	"context"
 
 	"github.com/cockroachdb/errors"
+	"github.com/cockroachdb/pebble/internal/base"
 	"github.com/cockroachdb/pebble/internal/bytealloc"
 	"github.com/cockroachdb/pebble/objstorage"
 	"github.com/cockroachdb/pebble/objstorage/objstorageprovider"
@@ -57,7 +58,7 @@ func CopySpan(
 
 	// If our input has not filters, our output cannot have filters either.
 	if r.tableFilter == nil {
-		o.FilterPolicy = nil
+		o.FilterPolicy = base.NoFilterPolicy
 	}
 	o.TableFormat = r.tableFormat
 	// We don't want the writer to attempt to write out block property data in

sstable/options.go

@@ -174,7 +174,7 @@ type WriterOptions struct {
 	// One such implementation is bloom.FilterPolicy(10) from the pebble/bloom
 	// package.
 	//
-	// The default value means to use no filter.
+	// The default value is NoFilterPolicy.
 	FilterPolicy FilterPolicy
 
 	// FilterType defines whether an existing filter policy is applied at a
@@ -348,5 +348,8 @@ func (o WriterOptions) ensureDefaults() WriterOptions {
 		(o.Compression == block.MinLZCompression && o.TableFormat < TableFormatPebblev6) {
 		o.Compression = block.SnappyCompression
 	}
+	if o.FilterPolicy == nil {
+		o.FilterPolicy = base.NoFilterPolicy
+	}
 	return o
 }

sstable/rowblk_writer.go

@@ -1742,7 +1742,7 @@ func newRowWriter(writable objstorage.Writable, o WriterOptions) *RawRowWriter {
 		return w
 	}
 
-	if o.FilterPolicy != nil {
+	if o.FilterPolicy != base.NoFilterPolicy {
 		switch o.FilterType {
 		case TableFilter:
 			w.filter = newTableFilterWriter(o.FilterPolicy)

sstable/suffix_rewriter.go

@@ -98,7 +98,7 @@ func rewriteKeySuffixesInBlocks(
 	case props.ComparerName != o.Comparer.Name:
 		return nil, TableFormatUnspecified, errors.Errorf("mismatched Comparer %s vs %s, replacement requires same splitter to copy filters",
 			props.ComparerName, o.Comparer.Name)
-	case o.FilterPolicy != nil && props.FilterPolicyName != o.FilterPolicy.Name():
+	case props.FilterPolicyName != o.FilterPolicy.Name():
 		return nil, TableFormatUnspecified, errors.New("mismatched filters")
 	}