Fix transaction in UpdateAndFindMinSyncedVersionVector (#1050)

This commit resolves an issue where the PushPull operation does not
function correctly when using the Memory DB.

UpdateAndFindMinSyncedVersionVector was previously set to start in
write mode, which causes it to simply read documents. However, inside
this function, it calls UpdateVersionVector, which attempts to start
in write mode again, resulting in a deadlock scenario where the
transaction cannot be acquired, causing an infinite wait.

server/backend/database/database.go

@@ -271,9 +271,9 @@ type Database interface {
 		serverSeq int64,
 	) (*time.Ticket, error)
 
-	// UpdateAndFindMinSyncedVersionVectorAfterPushPull updates the given serverSeq of the given client
+	// UpdateAndFindMinSyncedVersionVector updates the given serverSeq of the given client
 	// and returns the SyncedVersionVector of the document.
-	UpdateAndFindMinSyncedVersionVectorAfterPushPull(
+	UpdateAndFindMinSyncedVersionVector(
 		ctx context.Context,
 		clientInfo *ClientInfo,
 		docRefKey types.DocRefKey,

server/backend/database/memory/database.go

@@ -1312,9 +1312,9 @@ func (d *DB) UpdateVersionVector(
 	return nil
 }
 
-// UpdateAndFindMinSyncedVersionVectorAfterPushPull updates the given serverSeq of the given client
+// UpdateAndFindMinSyncedVersionVector updates the given serverSeq of the given client
 // and returns the SyncedVersionVector of the document.
-func (d *DB) UpdateAndFindMinSyncedVersionVectorAfterPushPull(
+func (d *DB) UpdateAndFindMinSyncedVersionVector(
 	ctx context.Context,
 	clientInfo *database.ClientInfo,
 	docRefKey types.DocRefKey,
@@ -1338,7 +1338,7 @@ func (d *DB) UpdateAndFindMinSyncedVersionVectorAfterPushPull(
 	}
 
 	// 02. Find all version vectors of the given document from DB.
-	txn := d.db.Txn(true)
+	txn := d.db.Txn(false)
 	defer txn.Abort()
 	iterator, err := txn.Get(tblVersionVectors, "doc_id", docRefKey.DocID.String())
 	if err != nil {

server/backend/database/mongo/client.go

@@ -1197,8 +1197,8 @@ func (c *Client) UpdateAndFindMinSyncedTicket(
 	), nil
 }
 
-// UpdateAndFindMinSyncedVersionVectorAfterPushPull returns min synced version vector
-func (c *Client) UpdateAndFindMinSyncedVersionVectorAfterPushPull(
+// UpdateAndFindMinSyncedVersionVector returns min synced version vector
+func (c *Client) UpdateAndFindMinSyncedVersionVector(
 	ctx context.Context,
 	clientInfo *database.ClientInfo,
 	docRefKey types.DocRefKey,

server/packs/packs.go

@@ -132,7 +132,7 @@ func PushPull(
 	// 05. update and find min synced version vector for garbage collection.
 	// NOTE(hackerwins): Since the client could not receive the response, the
 	// requested seq(reqPack) is stored instead of the response seq(resPack).
-	minSyncedVersionVector, err := be.DB.UpdateAndFindMinSyncedVersionVectorAfterPushPull(
+	minSyncedVersionVector, err := be.DB.UpdateAndFindMinSyncedVersionVector(
 		ctx,
 		clientInfo,
 		docRefKey,