pebble: deflake TestCompactionDeleteOnlyHints

maybe-compact was previously waiting on compactingCount to be 0 before reading
the collected compaction info. This observation was flaky, as compactingCount is
updated just before another call to `maybeScheduleCompaction`, with the mutex
being dropped in between.

Now, we observe both `compactingCount` and a new field, `compactProcesses`,
which track the number of calls to compact which still need to perform the
compaction scheduling step.

Fixes: #5351

Author: xinhaoz

compaction.go

@@ -2123,6 +2123,7 @@ func (d *DB) runPickedCompaction(pc pickedCompaction, grantHandle CompactionGran
 	}
 
 	d.mu.compact.compactingCount++
+	d.mu.compact.compactProcesses++
 	c := pc.ConstructCompaction(d, grantHandle)
 	c.AddInProgressLocked(d)
 	go func() {
@@ -2281,6 +2282,7 @@ func (d *DB) tryScheduleDeleteOnlyCompaction() bool {
 	if len(inputs) > 0 {
 		c := newDeleteOnlyCompaction(d.opts, v, inputs, d.timeNow(), resolvedHints, exciseEnabled)
 		d.mu.compact.compactingCount++
+		d.mu.compact.compactProcesses++
 		c.AddInProgressLocked(d)
 		go d.compact(c, nil)
 		return true
@@ -2655,6 +2657,7 @@ func (d *DB) compact(c compaction, errChannel chan error) {
 			d.mu.Lock()
 			defer d.mu.Unlock()
 			d.maybeScheduleCompaction()
+			d.mu.compact.compactProcesses--
 			d.mu.compact.cond.Broadcast()
 		}()
 	})

compaction_test.go

@@ -1226,23 +1226,14 @@ func runCompactionTest(
 			err := func() error {
 				d.mu.Lock()
 				defer d.mu.Unlock()
-				prevCount := d.mu.versions.metrics.Compact.Count
 				prev := d.opts.DisableAutomaticCompactions
 				d.opts.DisableAutomaticCompactions = false
-				err := try(100*time.Microsecond, 60*time.Second, func() error {
-					d.maybeScheduleCompaction()
-					for d.mu.compact.compactingCount > 0 {
-						d.mu.compact.cond.Wait()
-					}
-					compactions := d.mu.versions.metrics.Compact.Count - prevCount
-					if compactions < expectedCount {
-						return errors.Errorf("expectedCount at least %d automatic compaction(s), got %d, total: %d",
-							expectedCount, compactions, d.mu.versions.metrics.Compact.Count)
-					}
-					return nil
-				})
+				d.maybeScheduleCompaction()
+				for d.mu.compact.compactProcesses > 0 {
+					d.mu.compact.cond.Wait()
+				}
 				d.opts.DisableAutomaticCompactions = prev
-				return err
+				return nil
 			}()
 			if err != nil {
 				return err.Error() + "\n" + describeLSM(d, verbose)
@@ -1688,7 +1679,7 @@ func TestCompactionDeleteOnlyHints(t *testing.T) {
 
 	compactInfo = nil
 	compactionString := func() string {
-		for d.mu.compact.compactingCount > 0 {
+		for d.mu.compact.compactProcesses > 0 {
 			d.mu.compact.cond.Wait()
 		}
 		slices.SortFunc(compactInfo, func(a, b CompactionInfo) int {
@@ -1939,7 +1930,7 @@ func TestCompactionTombstones(t *testing.T) {
 	var compactInfo []*CompactionInfo // protected by d.mu
 
 	compactionString := func() string {
-		for d.mu.compact.compactingCount > 0 {
+		for d.mu.compact.compactProcesses > 0 {
 			d.mu.compact.cond.Wait()
 		}
 

db.go

@@ -418,6 +418,12 @@ type DB struct {
 			flushing bool
 			// The number of ongoing non-download compactions.
 			compactingCount int
+			// The number of calls to compact that have not yet finished. This is different
+			// from compactingCount, as calls to compact will attempt to schedule and run
+			// follow-up compactions after the current compaction finishes, dropping db.mu
+			// in between updating compactingCount and the scheduling operation. This value is
+			// used in tests in order to track when all compaction activity has finished.
+			compactProcesses int
 			// The number of download compactions.
 			downloadingCount int
 			// The list of deletion hints, suggesting ranges for delete-only

testdata/compaction/l0_to_lbase_compaction

@@ -24,7 +24,7 @@ L0.0:
   000009:[vhn@1#14977,SET-zzz@1#18287,SET]
 
 
-auto-compact count=3
+auto-compact
 ----
 L6:
   000006:[a@1#10,SET-hci@1#4995,SET]