add gc options (#828)

Signed-off-by: weedge <[email protected]>
Co-authored-by: disksing <[email protected]>

examples/gcworker/gcworker.go

@@ -21,6 +21,7 @@ import (
 	"time"
 
 	"github.com/tikv/client-go/v2/oracle"
+	"github.com/tikv/client-go/v2/tikv"
 	"github.com/tikv/client-go/v2/txnkv"
 )
 
@@ -36,10 +37,15 @@ func main() {
 		panic(err)
 	}
 
-	sysSafepoint, err := client.GC(context.Background(), *safepoint)
+
+	sysSafepoint, err := client.GC(context.Background(), *safepoint, tikv.WithConcurrency(10))
 	if err != nil {
 		panic(err)
 	}
 	fmt.Printf("Finished GC, expect safepoint:%d(%+v),real safepoint:%d(+%v)\n", *safepoint, oracle.GetTimeFromTS(*safepoint), sysSafepoint, oracle.GetTimeFromTS(sysSafepoint))
 
+	err = client.Close()
+	if err != nil {
+		panic(err)
+	}
 }

tikv/gc.go

@@ -50,15 +50,36 @@ import (
 //
 // GC is a simplified version of [GC in TiDB](https://docs.pingcap.com/tidb/stable/garbage-collection-overview).
 // We skip the second step "delete ranges" which is an optimization for TiDB.
-func (s *KVStore) GC(ctx context.Context, safepoint uint64) (newSafePoint uint64, err error) {
-	err = s.resolveLocks(ctx, safepoint, 8)
+func (s *KVStore) GC(ctx context.Context, safepoint uint64, opts ...GCOpt) (newSafePoint uint64, err error) {
+	// default concurrency 8
+	opt := &gcOption{concurrency: 8}
+	// Apply gc options.
+	for _, o := range opts {
+		o(opt)
+	}
+
+	err = s.resolveLocks(ctx, safepoint, opt.concurrency)
 	if err != nil {
 		return
 	}
 
 	return s.pdClient.UpdateGCSafePoint(ctx, safepoint)
 }
 
+type gcOption struct {
+	concurrency int
+}
+
+// GCOpt gc options
+type GCOpt func(*gcOption)
+
+// WithConcurrency is used to set gc RangeTaskRunner concurrency.
+func WithConcurrency(concurrency int) GCOpt {
+	return func(opt *gcOption) {
+		opt.concurrency = concurrency
+	}
+}
+
 func (s *KVStore) resolveLocks(ctx context.Context, safePoint uint64, concurrency int) error {
 	handler := func(ctx context.Context, r kv.KeyRange) (rangetask.TaskStat, error) {
 		return s.resolveLocksForRange(ctx, safePoint, r.StartKey, r.EndKey)