A programmer may choose between four operation modes using the ResourceOptions.CmdExecMode property:

An application may check TADCommand.State or TADAdaptedDataSet.Command.State for an operation status:

For example: 

ADQuery1.ResourceOptions.CmdExecMode := amAsync;
ADQuery1.Open;
while ADQuery1.Command.State = csExecuting do begin
  // do something while query is executing
end;

With help of TADGUIxAsyncExecuteDialog component, in the amCancelDialog mode a user may be notified about long running operations and have an ability to cancel operation: 

To use the dialog component, drop it on a form. No additional setup is required. Read more about modes and operation notification events at ResourceOptions.CmdExecMode property description. 

When an application needs to open a query pure asynchronously (amAsync) and the query is bind to the GUI using TDataSource, then before opening the query TDataSource must be disconnected from the query and after opening connected back. For example: 

procedure TForm1.BeforeOpen(DataSet: TDataSet);
begin
  DataSource1.DataSet := nil;
end;

procedure TForm1.AfterOpen(DataSet: TDataSet);
begin
  DataSource1.DataSet := ADQuery1;
  ADQuery1.ResourceOptions.CmdExecMode := amBlocking;
end;

ADQuery1.BeforeOpen := ADQuery1BeforeOpen;
ADQuery1.AfterOpen := ADQuery1AfterOpen;
ADQuery1.ResourceOptions.CmdExecMode := amAsync;
ADQuery1.Open;

That is not required when amCancelDialog is used. Also fetching with GUI cannot be performed in amAsync mode. To perform opening a query and fetching large result set asynchronously set FetchOptions.Mode = fmAll. Then both operations will be performed as a single background task. Note, that it is only valid when you need a bi-directional dataset. 

To asynchronously execute Firebird query use separated transaction for this query. 

A programmer can specify the timeout for the data access operation using the ResourceOptions.CmdExecTimeout property. When an operation execution requires more than the specified time, then the execution will be canceled and exception will be raised. To catch a command timeout use the code: 

try
  // set timeout to 5 seconds
  ADQuery1.ResourceOptions.CmdExecTimeout := 5000;
  ADQuery1.ExecSQL;
except
  on E: EADDBEngineException do
    if E.Kind = ekCmdAborted then
      ; // command is aborted
end;

Alternatively application may cancel operation execution by calling dataset or command AbortJob method from other thread. Or call connection AbortJob method to cancel all operations on this connection. 

Note, that not all AnyDAC drivers and DBMS are supporting execution cancellation. Also the cancellation may be performed not immediately, when A DBMS is performing some critical operations. The following table lists supported combinations:

Execution of the multiple asynchronous queries in parallel is not supported by AnyDAC, due to the general multi-threading principle. To workaround that consider the options:

• group few queries into a stored procedure and call the procedure asynchronously;
• use a dedicated connection for each asynchronous query running in parallel;
• launch next asynchronous query after previous one is finished. For that use the AfterOpen and AfterExecute event handlers;
• finally application may create own threads and execute the DB tasks in these threads.