Fix zset can't add the same member with different scores

src/redis_zset.cc

@@ -2,9 +2,8 @@
 
 #include <math.h>
 #include <map>
-#include <limits>
-#include <cmath>
 #include <memory>
+#include <set>
 
 namespace Redis {
 
@@ -28,8 +27,24 @@ rocksdb::Status ZSet::Add(const Slice &user_key, uint8_t flags, std::vector<Memb
   WriteBatchLogData log_data(kRedisZSet);
   batch.PutLogData(log_data.Encode());
   std::string member_key;
-  for (size_t i = 0; i < mscores->size(); i++) {
+  std::set<std::string> added_member_keys;
+  for (int i = static_cast<int>(mscores->size()-1); i >= 0; i--) {
     InternalKey(ns_key, (*mscores)[i].member, metadata.version).Encode(&member_key);
+
+    // Fix the corner case that adds the same member which may add the score
+    // column family many times and cause problems in the ZRANGE command.
+    //
+    // For example, we add members with `ZADD mykey 1 a 2 a` and `ZRANGE mykey 0 1`
+    // return only one member(`a`) was expected but got the member `a` twice now.
+    //
+    // The root cause of this issue was the score key  was composed by member and score,
+    // so the last one can't overwrite the previous when the score was different.
+    // A simple workaround was add those members with reversed order and skip the member if has added.
+    if (added_member_keys.find(member_key) != added_member_keys.end()) {
+      continue;
+    }
+    added_member_keys.insert(member_key);
+
     if (metadata.size > 0) {
       std::string old_score_bytes;
       s = db_->Get(rocksdb::ReadOptions(), member_key, &old_score_bytes);

tests/tcl/tests/unit/type/zset.tcl

@@ -24,6 +24,17 @@ start_server {tags {"zset"}} {
             assert_equal {y x z} [r zrange ztmp 0 -1]
         }
 
+        test "ZSET basic ZADD the same member with different scores - $encoding" {
+            r del ztmp
+            assert_equal 1 [r zadd ztmp 10 x 20 x]
+            assert_equal {x} [r zrange ztmp 0 -1]
+            assert_equal 20 [r zscore ztmp x]
+
+            assert_equal 2 [r zadd ztmp 30 x 40 y 50 z]
+            assert_equal {x y z} [r zrange ztmp 0 -1]
+            assert_equal 30 [r zscore ztmp x]
+        }
+
         test "ZSET element can't be set to NaN with ZADD - $encoding" {
             assert_error "*float*" {r zadd myzset nan abc}
         }