From 337fc3d6fd8bc672f3e038f8046d2edda5b9eb18 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Mon, 3 Feb 2025 11:28:48 +0100
Subject: [PATCH] Don't use threaded VADD in replicas, lua, multi.

---
 vset.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/vset.c b/vset.c
index 12ad472842..308d187563 100644
--- a/vset.c
+++ b/vset.c
@@ -297,13 +297,6 @@ int VADD_CASReply(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
         RedisModule_DictSet(vset->dict,val,newnode);
         val = NULL; // Don't free it later.
 
-        /* FIXME: probably it's better to drop the CAS argument when
-         * replicating. Other VADDs with CAS against the same item may arrive
-         * and can be executed out of order. Also DEL commands may arrive
-         * while the VADD is in progress.
-         *
-         * The problem of dropping CAS however is that the replica may no
-         * longer be able to keep with the insertion load. */
         RedisModule_ReplicateVerbatim(ctx);
     }
 
@@ -358,6 +351,20 @@ int VADD_RedisCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
         }
     }
 
+    /* Drop CAS if this is a replica and we are getting the command from the
+     * replication link: we want to add/delete items in the same order as
+     * the master, while with CAS the timing would be different.
+     *
+     * Also for Lua scripts and MULTI/EXEC, we want to run the command
+     * on the main thread. */
+    if (RedisModule_GetContextFlags(ctx) &
+            (REDISMODULE_CTX_FLAGS_REPLICATED|
+             REDISMODULE_CTX_FLAGS_LUA|
+             REDISMODULE_CTX_FLAGS_MULTI))
+    {
+        cas = 0;
+    }
+
     /* Open/create key */
     RedisModuleKey *key = RedisModule_OpenKey(ctx,argv[1],
         REDISMODULE_READ|REDISMODULE_WRITE);