enh(sync): add syncStartStandBy

include/libs/sync/sync.h

@@ -144,6 +144,7 @@ int32_t     syncInit();
 void        syncCleanUp();
 int64_t     syncOpen(const SSyncInfo* pSyncInfo);
 void        syncStart(int64_t rid);
+void        syncStartStandBy(int64_t rid);
 void        syncStop(int64_t rid);
 int32_t     syncReconfig(int64_t rid, const SSyncCfg* pSyncCfg);
 ESyncState  syncGetMyRole(int64_t rid);

source/libs/sync/inc/syncInt.h

@@ -247,6 +247,7 @@ typedef struct SSyncNode {
 // open/close --------------
 SSyncNode* syncNodeOpen(const SSyncInfo* pSyncInfo);
 void       syncNodeStart(SSyncNode* pSyncNode);
+void       syncNodeStartStandBy(SSyncNode* pSyncNode);
 void       syncNodeClose(SSyncNode* pSyncNode);
 
 // ping --------------

source/libs/sync/src/syncMain.c

@@ -103,6 +103,16 @@ void syncStart(int64_t rid) {
   taosReleaseRef(tsNodeRefId, pSyncNode->rid);
 }
 
+void syncStartStandBy(int64_t rid) {
+  SSyncNode* pSyncNode = (SSyncNode*)taosAcquireRef(tsNodeRefId, rid);
+  if (pSyncNode == NULL) {
+    return;
+  }
+  syncNodeStartStandBy(pSyncNode);
+
+  taosReleaseRef(tsNodeRefId, pSyncNode->rid);
+}
+
 void syncStop(int64_t rid) {
   SSyncNode* pSyncNode = (SSyncNode*)taosAcquireRef(tsNodeRefId, rid);
   if (pSyncNode == NULL) {
@@ -524,6 +534,17 @@ void syncNodeStart(SSyncNode* pSyncNode) {
   assert(ret == 0);
 }
 
+void syncNodeStartStandBy(SSyncNode* pSyncNode) {
+  // state change
+  pSyncNode->state = TAOS_SYNC_STATE_FOLLOWER;
+  syncNodeStopHeartbeatTimer(pSyncNode);
+
+  // reset elect timer, long enough
+  int32_t electMS = TIMER_MAX_MS;
+  int32_t ret = syncNodeRestartElectTimer(pSyncNode, electMS);
+  ASSERT(ret == 0);
+}
+
 void syncNodeClose(SSyncNode* pSyncNode) {
   int32_t ret;
   assert(pSyncNode != NULL);