plumb block level synthetic prefix support

This patch enables the db user to ingest a virtual sst with a synthetic prefix
and for higher level readers to plumb the synthetic prefix to the block
iterator which will conduct prefix synthesis.

Note that the db user can still ingest a virtual sst with a prefix _replacement_
rule, by passing the virtual sst the original prefix and the replacement
prefix. This tranformation is different that block level prefix synthesis as it
replaces the original prefix with the new prefix.

Author: msbutler

ingest.go

@@ -1130,6 +1130,9 @@ type ExternalFile struct {
 	// is accessed as if those keys all instead have prefix SyntheticPrefix.
 	//
 	// SyntheticPrefix must be a prefix of both SmallestUserKey and LargestUserKey.
+	//
+	// NB: If the SyntheticPrefix is non-empty and the ContentPrefix is empty,
+	// then the read path will conduct block level prefix synthesis.
 	ContentPrefix, SyntheticPrefix []byte
 
 	// SyntheticSuffix will replace the suffix of every key in the file during

internal/manifest/version.go

@@ -294,9 +294,14 @@ func (m *FileMetadata) SyntheticSeqNum() sstable.SyntheticSeqNum {
 
 // IterTransforms returns an sstable.IterTransforms that has SyntheticSeqNum set as needed.
 func (m *FileMetadata) IterTransforms() sstable.IterTransforms {
+	var syntheticPrefix []byte
+	if m.PrefixReplacement != nil && !m.PrefixReplacement.UsePrefixReplacementIterator() {
+		syntheticPrefix = m.PrefixReplacement.SyntheticPrefix
+	}
 	return sstable.IterTransforms{
 		SyntheticSeqNum: m.SyntheticSeqNum(),
 		SyntheticSuffix: m.SyntheticSuffix,
+		SyntheticPrefix: syntheticPrefix,
 	}
 }
 

sstable/block_test.go

@@ -384,6 +384,7 @@ func (c *checker) check(
 			c.t.Logf("expected %q, got %q", eKey.UserKey, gKey.UserKey)
 			require.Equal(c.t, eKey, gKey)
 			require.Equal(c.t, eVal, gVal)
+			c.notValid = false
 		} else {
 			c.t.Logf("expected nil, got %q", gKey)
 			require.Nil(c.t, gKey)

sstable/reader.go

@@ -184,6 +184,11 @@ func (ss SyntheticSuffix) IsSet() bool {
 // with range keys cannot be iterated over with a synthetic prefix.
 type SyntheticPrefix []byte
 
+// IsSet returns true if the synthetic prefix is not enpty.
+func (sp SyntheticPrefix) IsSet() bool {
+	return len(sp) > 0
+}
+
 // rawTombstonesOpt is a Reader open option for specifying that range
 // tombstones returned by Reader.NewRangeDelIter() should not be
 // fragmented. Used by debug tools to get a raw view of the tombstones
@@ -431,6 +436,9 @@ func (r *Reader) NewRawRangeDelIter(transforms IterTransforms) (keyspan.Fragment
 	if transforms.SyntheticSuffix.IsSet() {
 		return nil, errors.AssertionFailedf("synthetic suffix not supported with range del iterator")
 	}
+	if transforms.SyntheticPrefix.IsSet() {
+		return nil, errors.AssertionFailedf("synthetic prefix not supported with range del iterator")
+	}
 	h, err := r.readRangeDel(nil /* stats */, nil /* iterStats */)
 	if err != nil {
 		return nil, err
@@ -459,6 +467,9 @@ func (r *Reader) NewRawRangeKeyIter(transforms IterTransforms) (keyspan.Fragment
 	if transforms.SyntheticSuffix.IsSet() {
 		return nil, errors.AssertionFailedf("synthetic suffix not supported with range key iterator")
 	}
+	if transforms.SyntheticPrefix.IsSet() {
+		return nil, errors.AssertionFailedf("synthetic prefix not supported with range key iterator")
+	}
 	h, err := r.readRangeKey(nil /* stats */, nil /* iterStats */)
 	if err != nil {
 		return nil, err

sstable/reader_common.go

@@ -80,6 +80,12 @@ type PrefixReplacement struct {
 	SyntheticPrefix []byte
 }
 
+// UsePrefixReplacementIterator returns true if the prefix replacement iterator
+// wrapper should be used.
+func (p *PrefixReplacement) UsePrefixReplacementIterator() bool {
+	return p != nil && len(p.ContentPrefix) > 0
+}
+
 // Apply replaces the content prefix in the key with the synthetic prefix.
 func (p *PrefixReplacement) Apply(key []byte) []byte {
 	return p.replace(key, p.ContentPrefix, p.SyntheticPrefix)

sstable/reader_iter_single_lvl.go

@@ -259,7 +259,7 @@ func (i *singleLevelIterator) maybeVerifyKey(
 		key := iKey.UserKey
 		v := i.vState
 		var uc, lc int
-		if p := v.prefixChange; p != nil {
+		if p := v.prefixChange; p != nil && len(p.ContentPrefix) > 0 {
 			if !bytes.HasPrefix(key, p.ContentPrefix) {
 				panic(fmt.Sprintf("key %q does not have content prefix %q", key, v.prefixChange.ContentPrefix))
 			}
@@ -273,7 +273,7 @@ func (i *singleLevelIterator) maybeVerifyKey(
 			uc = i.cmp(key, v.upper.UserKey)
 		}
 		if lc < 0 || uc > 0 || (uc == 0 && v.upper.IsExclusiveSentinel()) {
-			panic(fmt.Sprintf("key %q out of singleLeveliterator virtual bounds %s %s", key, v.lower, v.lower))
+			panic(fmt.Sprintf("key %q out of singleLeveliterator virtual bounds %s %s", key, v.lower.UserKey, v.upper.UserKey))
 		}
 	}
 	return iKey, val