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Mon, Jun 5 2006 1:04 AM | Permanent Link |
Oliver Bock | Some time ago, Ralf asked for the best technique for adding many records
in client/server mode. As I understand things, using DBISAM's ordinary mechanisms will be very slow because each insert requires a round trip to the server for the Post/Execute. That is, time cost will be latency * num_records * 2 Eryk suggested writing a server-side procedure to do the inserts. I have done this, but I was disappointed to find that my DBISAM's string remote parameters are not 8-bit clean. That is to say, a string containing null characters was truncated. Luckily it works using blob parameters. Oliver This code marshals an array of array of Variants into a string buffer. var buf: string; buf_pos, buf_len: Integer; procedure AppendBytes(const source; size: Integer); begin if buf_pos + size > buf_len then begin buf_len := buf_len * 2; SetLength(buf, buf_len); end; Move(source, buf[buf_pos + 1], size); buf_pos := buf_pos + size; end; procedure Append(v: Variant); var s: string; l: Integer; begin // We cannot marshal varAny, varDispatch, varUnknown, varArray, // varByRef or varOleStr (sorry Ole). if varString = VarType(v) then begin // String variants have their data following the TVarData. // Since the VString member is irrelevant, we use VInteger // to store the length. s := string(TVarData(v).VString); VarClear(v); l := Length(s); v := l; TVarData(v).VType := varString; AppendBytes(TVarData(v), SizeOf(TVarData)); TVarData(v).VType := varInteger; AppendBytes(s[1], l); end else begin // For simple types we can just marshal the TVarData. AppendBytes(TVarData(v), SizeOf(TVarData)); end; end; var row: TVariantDynArray; i, j: Integer; begin // Encode the rows in a big buffer for transmission over the // client/server link. Each element is a variant. The first // contains the number of rows, and is followed by each row. // Each row starts with the number of its elements and // continues with their contents. buf_pos := 0; buf_len := 10240; SetLength(buf, buf_len); Append(Length(rows)); for i := 0 to High(rows) do begin row := rows[i]; Append(Length(row)); for j := 0 to High(row) do Append(row[j]); end; SetLength(buf, buf_pos); And this code unpacks it: var buf: string; buf_pos: Integer; function ExtractVariant: Variant; var s: string; pv: PVarData; l: Integer; begin pv := PVarData(Addr(buf[buf_pos + 1])); buf_pos := buf_pos + SizeOf(TVarData); if pv.VType = varString then begin l := pv.VInteger; SetLength(s, l); Move(buf[buf_pos + 1], s[1], l); result := s; buf_pos := buf_pos + l; end else Move(pv^, result, SizeOf(TVarData)); end; var rows: TVariantRows; row: TVariantDynArray; row_count, col_count, i, j: Integer; begin buf := session.RemoteParamByName('row_buffer').AsBlob; buf_pos := 0; row_count := ExtractVariant; SetLength(rows, row_count); for i := 0 to High(rows) do begin col_count := ExtractVariant; SetLength(rows[i], col_count); row := rows[i]; for j := 0 to High(row) do row[j] := ExtractVariant; end; P.S. There is a subtly memory leak of strings in the unpacking code. Can you find it? |
Mon, Jun 5 2006 9:49 AM | Permanent Link |
Tim Young [Elevate Software] Elevate Software, Inc. ![]() | Oliver,
<< P.S. There is a subtly memory leak of strings in the unpacking code. Can you find it? >> Are we going to be graded on this, or do you really need to know where the leak is because you can't find it ? ![]() -- Tim Young Elevate Software www.elevatesoft.com |
Mon, Jun 5 2006 6:34 PM | Permanent Link |
Oliver Bock | Tim Young [Elevate Software] wrote:
> << P.S. There is a subtly memory leak of strings in the unpacking code. Can > you find it? >> > > Are we going to be graded on this, or do you really need to know where the > leak is because you can't find it ? ![]() You have discovered my cunning plan. I admit that I just don't know where the leak is, but I trust FastMM's report. Regards, Oliver |
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