Fix zset add the same member with different scores (#298)

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 one when the score was different.
A simple workaround was to add those members with reversed orders and skip the member if has added.

src/redis_zset.cc

@@ -5,6 +5,7 @@
 #include <limits>
 #include <cmath>
 #include <memory>
+#include <set>
 
 namespace Redis {
 
@@ -28,8 +29,24 @@ 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}
         }