compact: recover from panics

We currently have occasional panics in prod but it's unclear what blocks
are being compacted during the panic. Hence, add this extra bit so that
block IDs would be visible in the logs.

Signed-off-by: Giedrius Statkevičius <[email protected]>

pkg/compact/compact.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"path/filepath"
 	"sort"
+	"strings"
 	"sync"
 	"time"
 
@@ -884,6 +885,21 @@ func (cg *Group) Compact(ctx context.Context, dir string, planner Planner, comp
 		return false, ulid.ULID{}, errors.Wrap(err, "create compaction group dir")
 	}
 
+	defer func() {
+		if p := recover(); p != nil {
+			var sb strings.Builder
+
+			cgIDs := cg.IDs()
+			for i, blid := range cgIDs {
+				_, _ = sb.WriteString(blid.String())
+				if i < len(cgIDs)-1 {
+					_, _ = sb.WriteString(",")
+				}
+			}
+			rerr = fmt.Errorf("paniced while compacting %s: %v", sb.String(), p)
+		}
+	}()
+
 	errChan := make(chan error, 1)
 	err := tracing.DoInSpanWithErr(ctx, "compaction_group", func(ctx context.Context) (err error) {
 		shouldRerun, compID, err = cg.compact(ctx, subDir, planner, comp, blockDeletableChecker, compactionLifecycleCallback, errChan)