add-faq-about-cocurrent-writes error (#1597)

docs-2.0/20.appendix/0.FAQ.md

@@ -167,12 +167,17 @@ The reason for this error may be that the amount of data to be queried is too la
 - Extend the RPC connection timeout of the Graph service and the Storage service. Modify the value of `--storage_client_timeout_ms` in the `nebula-storaged.conf` file. This configuration is measured in milliseconds (ms). The default value is 60000ms.
 <!--Tip: Add `--local_config=true` at the beginning of the configuration file and restart the service.-->
 
-### "How to resolve the error `MetaClient.cpp:65] Heartbeat failed, status:Wrong cluster!` in `nebula-storaged.INFO`, or `HBProcessor.cpp:54] Reject wrong cluster host "x.x.x.x":9771!` in `nebula-metad.INFO`?
+### "How to resolve the error `MetaClient.cpp:65] Heartbeat failed, status:Wrong cluster!` in `nebula-storaged.INFO`, or `HBProcessor.cpp:54] Reject wrong cluster host "x.x.x.x":9771!` in `nebula-metad.INFO`?"
 
 The reason for this error may be that the user has modified the IP or the port information of the metad process, or the storage service has joined other clusters before. Possible solutions are as follows:
 
 Delete the `cluster.id` file in the installation directory where the storage machine is deployed (the default installation directory is `/usr/local/nebula`), and restart the storaged service.
 
+### "How to resolve the error `Storage Error: More than one request trying to add/update/delete one edge/vertex at he same time.`?"
+
+The reason for this error is that the current NebulaGraph version does not support concurrent requests to the same vertex or edge at the same time. To solve this error, re-execute your commands.
+
+
 ## About design and functions
 
 ### "How is the `time spent` value at the end of each return message calculated?"
@@ -193,11 +198,11 @@ Got 1 rows (time spent 1235/1934 us)
 
 - The second number `1934` shows the time spent from the client's perspective, that is, the time it takes for the client from sending a request, receiving a response, and displaying the result on the screen.
 
-### Why does the port number of the `nebula-storaged` process keep showing red after connecting to NebulaGraph?
+### "Why does the port number of the `nebula-storaged` process keep showing red after connecting to NebulaGraph?"
 
 Because the `nebula-storaged` process waits for `nebula-metad` to add the current Storage service during the startup process. The Storage works after it receives the ready signal. Starting from NebulaGraph 3.0.0, the Meta service cannot directly read or write data in the Storage service that you add in the configuration file. The configuration file only registers the Storage service to the Meta service. You must run the `ADD HOSTS` command to enable the Meta to read and write data in the Storage service. For more information, see [Manage Storage hosts](../4.deployment-and-installation/manage-storage-host.md).
 
-### Why is there no line separating each row in the returned result of NebulaGraph 2.6.0?
+### "Why is there no line separating each row in the returned result of NebulaGraph 2.6.0?"
 
 This is caused by the release of NebulaGraph Console 2.6.0, not the change of NebulaGraph core. And it will not affect the content of the returned data itself.
 
@@ -282,11 +287,11 @@ You can use [NebulaGraph Algorithm](../graph-computing/nebula-algorithm.md).
 Or get vertices by each tag, and then group them by yourself.
 
 
-### Can non-English characters be used as identifiers, such as the names of graph spaces, tags, edge types, properties, and indexes?
+### "Can non-English characters be used as identifiers, such as the names of graph spaces, tags, edge types, properties, and indexes?"
 
 Yes, for more information, see [Keywords and reserved words](../3.ngql-guide/1.nGQL-overview/keywords-and-reserved-words.md).
 
-### "How to get the out-degree/the in-degree of a vertex with a given name"?
+### "How to get the out-degree/the in-degree of a vertex with a given name?"
 
 The out-degree of a vertex refers to the number of edges starting from that vertex, while the in-degree refers to the number of edges pointing to that vertex.