[fpc-devel] TDataset.ClearBuffers change in svn revision 3138

[Luiz Americo Pereira Camara]

Joost van der Sluis escreveu:
> On Mon, 2006-04-03 at 21:29 -0300, Luiz Americo Pereira Camara wrote:
>   
>> In revision 3138 TDataset.Clearbuffers call InternalInitRecord to empty 
>> the ActiveBuffer. I have two comments:
>>     
>
>   
>> - In DoInsertAppend InternalInitRecord will be called twice: one through 
>> ClearBuffers and other through InitRecord
>>     
>
> Yes, but twice for very different records, and only if it's an append.
> That's because 'append' effectively does a 'last' and then 'insert'.
> That it's called for the insert is logical. For the 'last'-part, see
> below:
>
>   
>> - ClearBuffers is called in First, Last, Resync: in this situations is 
>> desired to clear the ActiveBuffer?
>>     
>
> It is in the case of Resync. If a 'fuzzy resync' occurs that is most
> often because that the dataset is empty all of a sudden. For example if
> the last record is deleted. Or, for sqldb, if there are records added to
> a empty dataset, and cancelupdates is called.
> If InternalInitRecord isn't called then, you will still see the data of
> the latest record before the dataset became empty. If that record isn't
> cleared with InternalInitRecord, it will look like if there is still
> data. (although IsEmpty is true)
>
> So I've first added InternalInitRecord to Resync, but then I saw
> ClearBuffers and found it more logical to do it there. Since
> ClearBuffers clears the buffers if the dataset gets empty.
>
> Only I haven't thought about it that First and Last also calls it. On
> the other hand, if one does a 'first' and the dataset seems to be empty,
> the active record should be cleared. But I think you'll never encounter
> this problem, since the dataset most probably already was empty before
> the 'last' or 'first' calls...
>
> So, I think calling it in ClearBuffers is more logical, doing it in
> resync is somewhat better for performance?
>   
I understood that the only place that it's necessary is inside Resync. 
If so i am in favour of adding directly to it since won't hurt the 
readability, the functionality or the code size since is only a line of 
code. The performance will suffer  mainly because of the call inside 
InsertAppend (more or less depending of the TDataset implementation) . 
Anyway i think we should keep TDataset as fast as possible.

Luiz