From 30bba7f7de265db652d958f8fd8005191c560efa Mon Sep 17 00:00:00 2001
From: John Sully <john@csquare.ca>
Date: Sun, 26 Dec 2021 05:16:58 -0500
Subject: [PATCH] Fix partial sync failures

Former-commit-id: 7e9f7c0c4f520392a930ab72951e287f52c711ab
---
 src/replication.cpp | 22 ++++++++++++----------
 src/server.cpp      | 18 ++++++++++++------
 2 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/src/replication.cpp b/src/replication.cpp
index 77fc8a564..b1ad41b14 100644
--- a/src/replication.cpp
+++ b/src/replication.cpp
@@ -2165,18 +2165,20 @@ void saveMasterStatusToStorage(bool fShutdown)
         g_pserver->metadataDb->insert("repl-offset", 11, &g_pserver->master_repl_offset, sizeof(g_pserver->master_repl_offset), true);
     else
         g_pserver->metadataDb->insert("repl-offset", 11, &tmp, sizeof(g_pserver->master_repl_offset), true);
+
     if (g_pserver->fActiveReplica || (!listLength(g_pserver->masters) && g_pserver->repl_backlog)) {
-        g_pserver->metadataDb->insert("repl-stream-db", 14, g_pserver->replicaseldb == -1 ? 0 : &g_pserver->replicaseldb,
-                                        g_pserver->replicaseldb == -1 ? 0 : sizeof(g_pserver->replicaseldb), true);
-    }
+        int zero = 0;
+        g_pserver->metadataDb->insert("repl-stream-db", 14, g_pserver->replicaseldb == -1 ? &zero : &g_pserver->replicaseldb,
+                                        sizeof(g_pserver->replicaseldb), true);
+    } else {
+        struct redisMaster *miFirst = (redisMaster*)(listLength(g_pserver->masters) ? listNodeValue(listFirst(g_pserver->masters)) : NULL);
 
-    struct redisMaster *miFirst = (redisMaster*)(listLength(g_pserver->masters) ? listNodeValue(listFirst(g_pserver->masters)) : NULL);
-
-    if (miFirst && miFirst->master) {
-        g_pserver->metadataDb->insert("repl-stream-db", 14, &miFirst->master->db->id, sizeof(miFirst->master->db->id), true);
-    }
-    else if (miFirst && miFirst->cached_master) {
-        g_pserver->metadataDb->insert("repl-stream-db", 14, &miFirst->cached_master->db->id, sizeof(miFirst->cached_master->db->id), true);
+        if (miFirst && miFirst->master) {
+            g_pserver->metadataDb->insert("repl-stream-db", 14, &miFirst->master->db->id, sizeof(miFirst->master->db->id), true);
+        }
+        else if (miFirst && miFirst->cached_master) {
+            g_pserver->metadataDb->insert("repl-stream-db", 14, &miFirst->cached_master->db->id, sizeof(miFirst->cached_master->db->id), true);
+        }
     }
 
     if (listLength(g_pserver->masters) == 0) {
diff --git a/src/server.cpp b/src/server.cpp
index 8c0f9315b..2bc2f507c 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -3397,7 +3397,6 @@ int restartServer(int flags, mstime_t delay) {
 
     if (flags & RESTART_SERVER_GRACEFULLY) {
         if (g_pserver->m_pstorageFactory) {
-            saveMasterStatusToStorage(true);
             for (int idb = 0; idb < cserver.dbnum; ++idb) {
                 g_pserver->db[idb]->storageProviderDelete();
             }
@@ -4003,14 +4002,21 @@ void initServer(void) {
                 }
             });
             g_pserver->metadataDb->retrieve("repl-offset", 11, [&](const char *, size_t, const void *data, size_t cb){
-                if (cb == sizeof(g_pserver->replid)) {
+                if (cb == sizeof(g_pserver->master_repl_offset)) {
                     g_pserver->master_repl_offset = *(long long*)data;
                 }
             });
 
+            int repl_stream_db = -1;
+            g_pserver->metadataDb->retrieve("repl-stream-db", 14, [&](const char *, size_t, const void *data, size_t){
+                repl_stream_db = *(int*)data;
+            });
+
+            /* !!! AFTER THIS POINT WE CAN NO LONGER READ FROM THE META DB AS IT WILL BE OVERWRITTEN !!! */
+            // replicationCacheMasterUsingMyself triggers the overwrite 
+
             listIter li;
             listNode *ln;
-                
             listRewind(g_pserver->masters, &li);
             while ((ln = listNext(&li)))
             {
@@ -4019,9 +4025,7 @@ void initServer(void) {
                 * information, in order to allow partial resynchronizations
                 * with masters. */
                 replicationCacheMasterUsingMyself(mi);
-                g_pserver->metadataDb->retrieve("repl-stream-db", 14, [&](const char *, size_t, const void *data, size_t){
-                    selectDb(mi->cached_master, *(int*)data);
-                });
+                selectDb(mi->cached_master, repl_stream_db);
             }
         }
     }
@@ -4031,6 +4035,8 @@ void initServer(void) {
     {
         g_pserver->db[idb]->storageProviderInitialize();
     }
+
+    saveMasterStatusToStorage(false); // eliminate the repl-offset field
     
     /* Initialize ACL default password if it exists */
     ACLUpdateDefaultUserPassword(g_pserver->requirepass);