Optimize TSQL outbox cleanup by reducing batch size and adding rowloc…

…k hint (#1249)

src/SqlPersistence.Tests/ApprovalFiles/OutboxCommandTests.Cleanup.MsSql.approved.txt

@@ -1,4 +1,4 @@
 
-delete top (@BatchSize) from [TheSchema].[TheTablePrefixOutboxData]
+delete top (@BatchSize) from [TheSchema].[TheTablePrefixOutboxData] with (rowlock)
 where Dispatched = 'true' and
       DispatchedAt < @DispatchedBefore

src/SqlPersistence/Outbox/OutboxPersister.cs

@@ -20,7 +20,7 @@ class OutboxPersister : IOutboxStorage
 
     public OutboxPersister(IConnectionManager connectionManager, SqlDialect sqlDialect, OutboxCommands outboxCommands,
         Func<ISqlOutboxTransaction> outboxTransactionFactory,
-        int cleanupBatchSize = 10000)
+        int cleanupBatchSize = 4000) // Keep below 4000 to prevent lock escalation
     {
         this.connectionManager = connectionManager;
         this.sqlDialect = sqlDialect;

src/SqlPersistence/Outbox/SqlDialect_MsSqlServer.cs

@@ -75,8 +75,9 @@ internal override string GetOutboxPessimisticCompleteCommand(string tableName)
 
             internal override string GetOutboxCleanupCommand(string tableName)
             {
+                // Rowlock hint to prevent lock escalation which can result in INSERT's and competing cleanup to dead-lock
                 return $@"
-delete top (@BatchSize) from {tableName}
+delete top (@BatchSize) from {tableName} with (rowlock)
 where Dispatched = 'true' and
       DispatchedAt < @DispatchedBefore";
             }