MB-29483: Disable DCP cursor dropping

Disable DCP cursor dropping:

1. DCP replication consumers no longer request cursor dropping.
2. DCP producers default cursorDropping to false, and ignore any
   requests to enable it.

Change-Id: Ia9b5620d43c821eeaa32a7ec67df419a51acc089
Reviewed-on: http://review.couchbase.org/93534
Reviewed-by: Tim Bradgate <[email protected]>
Reviewed-by: Jim Walker <[email protected]>
Well-Formed: Build Bot <[email protected]>
Tested-by: Build Bot <[email protected]>

Author: daverigby

src/dcp/consumer.cc

@@ -123,7 +123,8 @@ DcpConsumer::DcpConsumer(EventuallyPersistentEngine &engine, const void *cookie,
     pendingSetPriority = true;
     pendingEnableExtMetaData = true;
     pendingEnableValueCompression = config.isDcpValueCompressionEnabled();
-    pendingSupportCursorDropping = true;
+    // MB-29369: Don't request cursor dropping.
+    pendingSupportCursorDropping = false;
 
     ExTask task = new Processor(&engine, this, 1);
     processorTaskId = ExecutorPool::get()->schedule(task, NONIO_TASK_IDX);

src/dcp/producer.cc

@@ -172,15 +172,10 @@ DcpProducer::DcpProducer(EventuallyPersistentEngine &e, const void *cookie,
     enableExtMetaData = false;
     enableValueCompression = false;
 
-    // Cursor dropping is disabled for replication connections by default,
-    // but will be enabled through a control message to support backward
-    // compatibility. For all other type of DCP connections, cursor dropping
-    // will be enabled by default.
-    if (name.find("replication") < name.length()) {
-        supportsCursorDropping = false;
-    } else {
-        supportsCursorDropping = true;
-    }
+    // MB-29369: Cursor dropping is currently disabled for all
+    // connections due to race condition which can result in skipping
+    // mutations.
+    supportsCursorDropping = false;
 
     backfillMgr.reset(new BackfillManager(&engine_));
 
@@ -584,11 +579,8 @@ ENGINE_ERROR_CODE DcpProducer::control(uint32_t opaque, const void* key,
         }
         return ENGINE_SUCCESS;
     } else if (strncmp(param, "supports_cursor_dropping", nkey) == 0) {
-        if (valueStr == "true") {
-            supportsCursorDropping = true;
-        } else {
-            supportsCursorDropping = false;
-        }
+        // MB-29369: Cursor dropping currently disabled. Ignore requests
+        // to enable.
         return ENGINE_SUCCESS;
     } else if (strncmp(param, "set_noop_interval", nkey) == 0) {
         if (parseUint32(valueStr.c_str(), &noopCtx.noopInterval)) {

tests/ep_testsuite_dcp.cc

@@ -2321,6 +2321,9 @@ static test_result test_dcp_agg_stats(ENGINE_HANDLE *h, ENGINE_HANDLE_V1 *h1) {
 
 static test_result test_dcp_cursor_dropping(ENGINE_HANDLE *h,
                                             ENGINE_HANDLE_V1 *h1) {
+    // MB-29369: Cursor dropping currently disabled
+    return SKIPPED;
+
     /* Initially write a few items */
     int num_items = 25;
     const int cursor_dropping_mem_thres_perc = 90;
@@ -2407,6 +2410,9 @@ static test_result test_dcp_cursor_dropping(ENGINE_HANDLE *h,
 
 static test_result test_dcp_cursor_dropping_backfill(ENGINE_HANDLE *h,
                                                      ENGINE_HANDLE_V1 *h1) {
+    // MB-29369: Cursor dropping currently disabled
+    return SKIPPED;
+
     /* Initially write a few items */
     int num_items = 50;
     const int cursor_dropping_mem_thres_perc = 90;
@@ -2907,10 +2913,13 @@ static uint32_t add_stream_for_consumer(ENGINE_HANDLE *h, ENGINE_HANDLE_V1 *h1,
         cb_assert(dcp_last_opaque != opaque);
     }
 
+    // MB-29369: Cursor dropping currently disabled.
+#if 0
     dcp_step(h, h1, cookie);
     cb_assert(dcp_last_op == PROTOCOL_BINARY_CMD_DCP_CONTROL);
     cb_assert(dcp_last_key.compare("supports_cursor_dropping") == 0);
     cb_assert(dcp_last_opaque != opaque);
+#endif
 
     checkeq(ENGINE_SUCCESS,
             h1->dcp.add_stream(h, cookie, opaque, vbucket, flags),