MB-41107: Add conflict_resolution_type=custom (dev preview)

Add a third enumeration value for conflict_resolution_type:
'custom'. This is currently treated identically to the "lww" value.

Change-Id: Ib0f191bf3068c15bb3dd3cb5a7a165a9a77fc4c3
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/137549
Tested-by: Build Bot <[email protected]>
Reviewed-by: James Harrison <[email protected]>

Author: daverigby

engines/ep/configuration.json

@@ -229,12 +229,14 @@
         },
         "conflict_resolution_type": {
             "default": "seqno",
+            "desr": "Conflict resolution mode to use for this Bucket",
             "dynamic": false,
             "type": "std::string",
             "validator": {
                 "enum": [
                     "seqno",
-                    "lww"
+                    "lww",
+                    "custom"
                 ]
             }
         },

engines/ep/src/ep_engine.cc

@@ -5259,13 +5259,13 @@ bool EventuallyPersistentEngine::decodeWithMetaOptions(
     bool check1 = generateCas == GenerateCas::Yes &&
                   checkConflicts == CheckConflicts::Yes;
 
-    // 2) If bucket is LWW and forceFlag is not set and GenerateCas::No
-    bool check2 = configuration.getConflictResolutionType() == "lww" &&
+    // 2) If bucket is LWW/Custom and forceFlag is not set and GenerateCas::No
+    bool check2 = configuration.getConflictResolutionType() != "seqno" &&
                   !forceFlag && generateCas == GenerateCas::No;
 
-    // 3) If bucket is not LWW then forceFlag must be false.
+    // 3) If bucket is seqno then forceFlag must be false.
     bool check3 =
-            configuration.getConflictResolutionType() != "lww" && forceFlag;
+            configuration.getConflictResolutionType() == "seqno" && forceFlag;
 
     // So if either check1/2/3 is true, return false
     return !(check1 || check2 || check3);

engines/ep/src/vbucket.cc

@@ -240,10 +240,12 @@ VBucket::VBucket(Vbid i,
       seqnoAckCb(std::move(seqnoAckCb)),
       manifest(std::move(manifest)),
       mayContainXattrs(mightContainXattrs) {
-    if (config.getConflictResolutionType().compare("lww") == 0) {
-        conflictResolver.reset(new LastWriteWinsResolution());
+    if (config.getConflictResolutionType() == "seqno") {
+        conflictResolver = std::make_unique<RevisionSeqnoResolution>();
     } else {
-        conflictResolver.reset(new RevisionSeqnoResolution());
+        // Both last-write-wins and custom conflict resolution are treated
+        // as LWW from KV-Engine's pov.
+        conflictResolver = std::make_unique<LastWriteWinsResolution>();
     }
 
     pendingOpsStart = std::chrono::steady_clock::time_point();