Please note the Edit below for a lot more information, and a possible solution
We recently modified a large Delphi application to use ADO connections and queries instead of BDE connections and queries. Since that change, performance has become terrible.
I've profiled the application and the bottleneck seems to be at the actual call to TADOQuery.Open. In other words, there isn't much I can do from a code standpoint to improve this, other than restructuring the application to actually use the database less.
Does anyone have suggestions about how to improve the performance of an ADO-connected Delphi application? I've tried both of the suggestions given here, with virtually no impact.
To give an idea of the performance difference, I benchmarked the same large operation:
We are using an Oracle back-end in a client-server environment. Local machines each maintain a separate connection to the database.
For the record, the connection string looks like this:
const
c_ADOConnString = 'Provider=OraOLEDB.Oracle.1;Persist Security Info=True;' +
'Extended Properties="plsqlrset=1";' +
'Data Source=DATABASE.DOMAIN.COM;OPTION=35;' +
'User ID=******;Password=*******';
To answer the questions posed by zendar:
I'm using Delphi 2007 on Windows Vista and XP.
The back end is an Oracle 10g database.
As indicated by the connection string, we are using the OraOLEDB driver.
The MDAC version on my benchmark machine is 6.0.
Edit:
Under the BDE, we had a lot of code that looked like this:
procedure MyBDEProc;
var
qry: TQuery;
begin
//fast under BDE, but slow under ADO!!
qry := TQuery.Create(Self);
try
with qry do begin
Database := g_Database;
Sql.Clear;
Sql.Add('SELECT');
Sql.Add(' FIELD1');
Sql.Add(' ,FIELD2');
Sql.Add(' ,FIELD3');
Sql.Add('FROM');
Sql.Add(' TABLE1');
Sql.Add('WHERE SOME_FIELD = SOME_CONDITION');
Open;
//do something
Close;
end; //with
finally
FreeAndNil(qry);
end; //try-finally
end; //proc
But we found that the call to Sql.Add is actually very expensive under ADO, because the QueryChanged event is fired every time you change the CommandText. So replacing the above with this was MUCH faster:
procedure MyADOProc;
var
qry: TADOQuery;
begin
//fast(er) under ADO
qry := TADOQuery.Create(Self);
try
with qry do begin
Connection := g_Connection;
Sql.Text := ' SELECT ';
+ ' FIELD1 '
+ ' ,FIELD2 '
+ ' ,FIELD3 '
+ ' FROM '
+ ' TABLE1 '
+ ' WHERE SOME_FIELD = SOME_CONDITION ';
Open;
//do something
Close;
end; //with
finally
FreeAndNil(qry);
end; //try-finally
end; //proc
Better yet, you can copy TADOQuery out of ADODB.pas, rename it under a new name, and rip out the QueryChanged event, which as far as I can tell, is not doing anything useful at all. Then use your new, modified version of TADOQuery, instead of the native one.
type
TADOQueryTurbo = class(TCustomADODataSet)
private
//
protected
procedure QueryChanged(Sender: TObject);
public
FSQL: TWideStrings;
FRowsAffected: Integer;
function GetSQL: TWideStrings;
procedure SetSQL(const Value: TWideStrings);
procedure Open;
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
function ExecSQL: Integer; {for TQuery compatibility}
property RowsAffected: Integer read FRowsAffected;
published
property CommandTimeout;
property DataSource;
property EnableBCD;
property ParamCheck;
property Parameters;
property Prepared;
property SQL: TWideStrings read FSQL write SetSQL;
end;
////////////////////////////////////////////////////////
////////////////////////////////////////////////////////
////////////////////////////////////////////////////////
constructor TADOQueryTurbo.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
FSQL := TWideStringList.Create;
TWideStringList(FSQL).OnChange := QueryChanged;
Command.CommandText := 'SQL'; { Do not localize }
end;
destructor TADOQueryTurbo.Destroy;
begin
inherited;
inherited Destroy;
FreeAndNil(FSQL);
end;
function TADOQueryTurbo.ExecSQL: Integer;
begin
CommandText := FSQL.Text;
inherited;
end;
function TADOQueryTurbo.GetSQL: TWideStrings;
begin
Result := FSQL;
end;
procedure TADOQueryTurbo.Open;
begin
CommandText := FSQL.Text;
inherited Open;
end;
procedure TADOQueryTurbo.QueryChanged(Sender: TObject);
begin
// if not (csLoading in ComponentState) then
// Close;
// CommandText := FSQL.Text;
end;
procedure TADOQueryTurbo.SetSQL(const Value: TWideStrings);
begin
FSQL.Assign(Value);
CommandText := FSQL.Text;
end;
See Question&Answers more detail:
os 
