db: fix SINGLEDEL, MERGE + DEL interaction

Previously, when a MERGE consumed a deletion tombstone during a compaction, the
MERGE key was transformed into a SET. This SET lost knowledge of the previous
deletion. Previously, a subsequent SingleDelete (intended to remove the MERGE
key) could elide the SET, resurrecting internal keys that were deleted by the
consumed deletion tombstone.

This commit adjusts the compaction iterator to produce a SETWITHDEL (see #1255)
that preserves knowledge of the consumed deletion tombstone. This ensures that
a SINGLEDEL that meets the merged key yields a DEL.

compaction_iter.go

@@ -522,7 +522,7 @@ func (i *compactionIter) Next() (*InternalKey, []byte) {
 				// into a SET.
 				var includesBase bool
 				switch i.key.Kind() {
-				case InternalKeyKindSet:
+				case InternalKeyKindSet, InternalKeyKindSetWithDelete:
 					includesBase = true
 				case InternalKeyKindMerge:
 				default:
@@ -832,7 +832,8 @@ func (i *compactionIter) mergeNext(valueMerger ValueMerger) stripeChangeType {
 			// We've hit a deletion tombstone. Return everything up to this point and
 			// then skip entries until the next snapshot stripe. We change the kind
 			// of the result key to a Set so that it shadows keys in lower
-			// levels. That is, MERGE+DEL -> SET.
+			// levels. That is, MERGE+DEL -> SETWITHDEL.
+			//
 			// We do the same for SingleDelete since SingleDelete is only
 			// permitted (with deterministic behavior) for keys that have been
 			// set once since the last SingleDelete/Delete, so everything
@@ -845,7 +846,7 @@ func (i *compactionIter) mergeNext(valueMerger ValueMerger) stripeChangeType {
 			// single Set, and then merge in any following Sets, but that is
 			// complicated wrt code and unnecessary given the narrow permitted
 			// use of SingleDelete.
-			i.key.SetKind(InternalKeyKindSet)
+			i.key.SetKind(InternalKeyKindSetWithDelete)
 			i.skip = true
 			return sameStripeSkippable
 

testdata/compaction_iter

@@ -787,7 +787,7 @@ iter
 first
 next
 ----
-a#6,1:b[base]
+a#6,18:b[base]
 .
 
 # Non-deterministic use of SINGLEDEL where there are two older SETs that have
@@ -803,7 +803,7 @@ iter
 first
 next
 ----
-a#6,1:b[base]
+a#6,18:b[base]
 .
 
 define
@@ -1067,29 +1067,29 @@ iter
 first
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 .
 
 iter allow-zero-seqnum=true
 first
 next
 ----
-a#0,1:5[base]
+a#0,18:5[base]
 .
 
 iter elide-tombstones=true
 first
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 .
 
 iter snapshots=2
 first
 next
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 a#1,2:1
 .
 
@@ -1098,7 +1098,7 @@ first
 next
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 a#1,2:1
 .
 

testdata/compaction_iter_delete_sized

@@ -786,7 +786,7 @@ iter
 first
 next
 ----
-a#6,1:b[base]
+a#6,18:b[base]
 .
 
 # Non-deterministic use of SINGLEDEL where there are two older SETs that have
@@ -802,7 +802,7 @@ iter
 first
 next
 ----
-a#6,1:b[base]
+a#6,18:b[base]
 .
 
 define
@@ -1066,29 +1066,29 @@ iter
 first
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 .
 
 iter allow-zero-seqnum=true
 first
 next
 ----
-a#0,1:5[base]
+a#0,18:5[base]
 .
 
 iter elide-tombstones=true
 first
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 .
 
 iter snapshots=2
 first
 next
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 a#1,2:1
 .
 
@@ -1097,7 +1097,7 @@ first
 next
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 a#1,2:1
 .
 
@@ -1863,7 +1863,7 @@ missized-dels=0
 
 # Regression test for #3087.
 #
-# Whne a DELSIZED and a SINGLEDEL meet in a compaction, a DEL key should be
+# When a DELSIZED and a SINGLEDEL meet in a compaction, a DEL key should be
 # emitted.
 
 define
@@ -1879,3 +1879,19 @@ next
 ----
 a#5,0:
 .
+
+# When a MERGE and a DEL[SIZED] meet in a compaction, a SETWITHDEL key (NOT a
+# SET) should be emitted. Otherwise, a sequence such as SINGLEDDEL, MERGE, DEL,
+# SET could result in the SET re-appearing.
+
+define
+a.MERGE.5:foo
+a.DEL.3:
+----
+
+iter
+first
+next
+----
+a#5,18:foo[base]
+.

testdata/compaction_iter_set_with_del

@@ -786,7 +786,7 @@ iter
 first
 next
 ----
-a#6,1:b[base]
+a#6,18:b[base]
 .
 
 # Non-deterministic use of SINGLEDEL where there are two older SETs that have
@@ -802,7 +802,7 @@ iter
 first
 next
 ----
-a#6,1:b[base]
+a#6,18:b[base]
 .
 
 define
@@ -1066,29 +1066,29 @@ iter
 first
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 .
 
 iter allow-zero-seqnum=true
 first
 next
 ----
-a#0,1:5[base]
+a#0,18:5[base]
 .
 
 iter elide-tombstones=true
 first
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 .
 
 iter snapshots=2
 first
 next
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 a#1,2:1
 .
 
@@ -1097,7 +1097,7 @@ first
 next
 next
 ----
-a#5,1:5[base]
+a#5,18:5[base]
 a#1,2:1
 .