Set aurora_replica_read_consistency to "session" before DML commands .Net6.0 + EFCore6 + Pomelo6 + AWS Aurora (MySQL 5.7)

The issue

I am using AWS Aurora MySQL. Following below article, I have created a secondary readonly cluster and enabled write-forwarding on it so that all write queries sent to secondary readonly cluster are forwarded to primary cluster.

https://aws.amazon.com/blogs/database/building-globally-distributed-mysql-applications-using-write-forwarding-in-amazon-aurora-global-database/

As mentioned in above post, it also requires to set parameter aurora_replica_read_consistency at session level. And I’ve set this in the init_connect like this: set @@aurora_replica_read_consistency=SESSION … so that it gets executed automatically when new client connects.

When testing write-queries in MySQL Workbench, it works perfectly and no additional change is required. The same behavior was expected in our .net6.0 application. However, when issuing a write-query in .net6.0 application using Pomelo 6.0.1, it throws an error as if aurora_replica_read_consistency is set to blank.

Exception message:
Stack trace: Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while saving the entity changes. See the inner exception for details.
 ---> MySqlConnector.MySqlException (0x80004005): The MySQL server is running with the --read-only option so it cannot execute this statement
   at MySqlConnector.Core.ServerSession.ReceiveReplyAsyncAwaited(ValueTask`1 task) in /_/src/MySqlConnector/Core/ServerSession.cs:line 954
   at MySqlConnector.Core.ResultSet.ReadResultSetHeaderAsync(IOBehavior ioBehavior) in /_/src/MySqlConnector/Core/ResultSet.cs:line 44
   at MySqlConnector.MySqlDataReader.ActivateResultSet(CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlDataReader.cs:line 127
   at MySqlConnector.MySqlDataReader.CreateAsync(CommandListPosition commandListPosition, ICommandPayloadCreator payloadCreator, IDictionary`2 cachedProcedures, IMySqlCommand command, CommandBehavior behavior, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlDataReader.cs:line 456
   at MySqlConnector.Core.CommandExecutor.ExecuteReaderAsync(IReadOnlyList`1 commands, ICommandPayloadCreator payloadCreator, CommandBehavior behavior, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/CommandExecutor.cs:line 56
   at MySqlConnector.MySqlCommand.ExecuteReaderAsync(CommandBehavior behavior, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlCommand.cs:line 330
   at MySqlConnector.MySqlCommand.ExecuteDbDataReaderAsync(CommandBehavior behavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlCommand.cs:line 323
   at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IList`1 entriesToSave, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(StateManager stateManager, Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.<>c__DisplayClass33_0`2.<<ExecuteAsync>b__0>d.MoveNext()

Do we need additional changes when using write-forward on AWS Aurora MySQL with Pomelo?

Further technical details

MySQL version: 5.7.12-log Operating system: AWS RDS Aurora Pomelo.EntityFrameworkCore.MySql version: 6.0.1 Microsoft.AspNetCore.App version:

Other details about my project setup: TargetFramework: .net6.0 WebAPI Project

[bgrainger]

Note that you will need to disable SSL with SslMode=None; for the packet capture to be useful. If that’s not possible (e.g., can’t be disabled on Aurora) then all the packets will be encrypted and I won’t be able to read them to see what’s going on.

[bgrainger]

Oddly, the first connection that gets created executes this query and gets back a result of SESSION, but subsequent connections execute the same query but get a blank result. Any idea why that would happen? Why would the init_connect SQL only get applied to the first connection created, but not the subsequent ones?

My guess would be connection pooling. MySqlConnection.Open doesn’t always result in a new connection being established to the database server (for performance). Most of the time, an existing connection is reused. Moreover, that connection is reset (to clear session variables, temp tables, etc.). My guess would be that in Aurora, this also clears the aurora_replica_read_consistency setting.

You could test this theory by adding Connection Reset = false; to your connection string.