[#421] Try using badger for the write-cache

Signed-off-by: Alejandro Lopez <a.lopez@yadro.com>

pkg/local_object_storage/writecache/writecachebbolt/mode.go

@@ -0,0 +1,75 @@
+package writecachebbolt
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
+	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/shard/mode"
+	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/trace"
+)
+
+// SetMode sets write-cache mode of operation.
+// When shard is put in read-only mode all objects in memory are flushed to disk
+// and all background jobs are suspended.
+func (c *cache) SetMode(m mode.Mode) error {
+	ctx, span := tracing.StartSpanFromContext(context.TODO(), "writecache.SetMode",
+		trace.WithAttributes(
+			attribute.String("mode", m.String()),
+		))
+	defer span.End()
+
+	err := c.setMode(ctx, m)
+	if err == nil {
+		c.metrics.SetMode(m)
+	}
+	return err
+}
+
+// setMode applies new mode. Must be called with cache.modeMtx lock taken.
+func (c *cache) setMode(ctx context.Context, m mode.Mode) error {
+	var err error
+	turnOffMeta := m.NoMetabase()
+
+	if turnOffMeta && !c.mode.NoMetabase() {
+		err = c.flush(ctx, true)
+		if err != nil {
+			return err
+		}
+	}
+
+	if c.db != nil {
+		if err = c.db.Close(); err != nil {
+			return fmt.Errorf("can't close write-cache database: %w", err)
+		}
+	}
+
+	// Suspend producers to ensure there are channel send operations in fly.
+	// flushCh is populated by `flush` with `modeMtx` taken, thus waiting until it is empty
+	// guarantees that there are no in-fly operations.
+	for len(c.flushCh) != 0 {
+		c.log.Info(logs.WritecacheWaitingForChannelsToFlush)
+		time.Sleep(time.Second)
+	}
+
+	if turnOffMeta {
+		c.mode = m
+		return nil
+	}
+
+	if err = c.openStore(m.ReadOnly()); err != nil {
+		return err
+	}
+
+	c.mode = m
+	return nil
+}
+
+// readOnly returns true if current mode is read-only.
+// `c.modeMtx` must be taken.
+func (c *cache) readOnly() bool {
+	return c.mode.ReadOnly()
+}