db: cap size of multi-level compactions at expanded bytes size

Previously, we had a missing check for the max "expanded" size
of a compaction being exceeded when we were trying to convert a
regular compaction to a multi-level compaction. This change adds
that check to prevent multi level compactions from getting too big.

Fixes #3120

compaction_picker.go

@@ -1683,6 +1683,13 @@ func (wa WriteAmpHeuristic) pick(
 	if !pcMulti.setupMultiLevelCandidate(opts, diskAvailBytes) {
 		return pcOrig
 	}
+	// We consider the addition of a level as an "expansion" of the compaction.
+	// If pcMulti is past the expanded compaction byte size limit already,
+	// we don't consider it.
+	if pcMulti.compactionSize() >= expandedCompactionByteSizeLimit(
+		opts, adjustedOutputLevel(pcMulti.outputLevel.level, pcMulti.baseLevel), diskAvailBytes) {
+		return pcOrig
+	}
 	picked := pcOrig
 	if pcMulti.predictedWriteAmp() <= pcOrig.predictedWriteAmp()+wa.AddPropensity {
 		picked = pcMulti

event.go

@@ -119,14 +119,18 @@ func (i CompactionInfo) SafeFormat(w redact.SafePrinter, _ rune) {
 		w.Printf("[JOB %d] compacting(%s) ",
 			redact.Safe(i.JobID),
 			redact.SafeString(i.Reason))
-		w.Printf("%s", i.Annotations)
+		if len(i.Annotations) > 0 {
+			w.Printf("%s ", i.Annotations)
+		}
 		w.Printf("%s; ", levelInfos(i.Input))
 		w.Printf("OverlappingRatio: Single %.2f, Multi %.2f", i.SingleLevelOverlappingRatio, i.MultiLevelOverlappingRatio)
 		return
 	}
 	outputSize := tablesTotalSize(i.Output.Tables)
 	w.Printf("[JOB %d] compacted(%s) ", redact.Safe(i.JobID), redact.SafeString(i.Reason))
-	w.Printf("%s", i.Annotations)
+	if len(i.Annotations) > 0 {
+		w.Printf("%s ", i.Annotations)
+	}
 	w.Print(levelInfos(i.Input))
 	w.Printf(" -> L%d [%s] (%s), in %.1fs (%.1fs total), output rate %s/s",
 		redact.Safe(i.Output.Level),

testdata/compaction_setup_inputs_multilevel_write_amp

@@ -273,7 +273,8 @@ init-multi-level(1,2,3)
 Original WriteAmp 2.25; ML WriteAmp 1.24
 Original OverlappingRatio 1.25; ML OverlappingRatio 0.24
 
-# If max size is exceeded, we no longer pick e-f in L2.
+# If max expanded size is exceeded, we don't add an extra level.
+
 setup-inputs avail-bytes=20 a a
 L1
   a.SET.1-c.SET.2 size=4
@@ -288,12 +289,6 @@ L1
   000001:[a#1,SET-c#2,SET]
 L2
   000002:[a#5,SET-d#6,SET]
-L3
-  000004:[a#3,SET-b#4,SET]
-  000005:[c#2,SET-g#2,SET]
-init-multi-level(1,2,3)
-Original WriteAmp 2.25; ML WriteAmp 1.44
-Original OverlappingRatio 1.25; ML OverlappingRatio 0.44
 
 # Don't init a multi-level compaction if the start level is L5.
 setup-inputs a a