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AnswerRe: Igroupping with Parallel Pin
Luc Pattyn1-Mar-20 9:04
sitebuilderLuc Pattyn1-Mar-20 9:04 
GeneralRe: Igroupping with Parallel Pin
Member 110035101-Mar-20 18:36
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GeneralRe: Igroupping with Parallel Pin
Pete O'Hanlon1-Mar-20 21:21
subeditorPete O'Hanlon1-Mar-20 21:21 
GeneralRe: Igroupping with Parallel Pin
Member 110035101-Mar-20 22:17
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GeneralRe: Igroupping with Parallel Pin
Pete O'Hanlon1-Mar-20 22:42
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GeneralRe: Igroupping with Parallel Pin
Richard Deeming1-Mar-20 23:57
mveRichard Deeming1-Mar-20 23:57 
Generaladd DISTINCT drop PARALLEL Pin
Luc Pattyn2-Mar-20 0:48
sitebuilderLuc Pattyn2-Mar-20 0:48 
Generaldrop TOLIST, avoid memory stress Pin
Luc Pattyn2-Mar-20 9:13
sitebuilderLuc Pattyn2-Mar-20 9:13 
Hi,

One more comment:

I'm not very familiar with LINQ and so I'm not sure I understand your code
lstFilters = (from tb in dbLinq.Table
                   group tb by new
                       {
                        tb.Date.Year
                       } into dates
                   select dates.Key.Year).ToList();

very well. It is my guess this is generting a "streamed Dictionary" where the Key is a year, and the Value is an enumerable holding all the table entries matching that year.

If so, calling ToList() on it will cause all this data to be stored in RAM, which implies
(a) the entire DB operation is performed "at once", not in chuncks (sabotaging any attempt for parallel
database accesses);
(b) all this data may amount to gigabytes, possibly causing memory stress and even copying stuff to disk; something the problem at hand does not really require.


You could try omitting ToList() but then AsParallel() might, I don't know, itself cause all data to be retrieved before anything happens. So if you want to keep as close as possible to that original code, I'd suggest you drop both ToList() and AsParallel().


However I still prefer my original suggestion, where an explicit database access is used to get distinctYears; and then a foreach that contains a LINQ or other piece of code to handle only the records pertaining to a particular year. This MSDN page[^] provides a normal example for the foreach content.
And I still would only consider parallelism if and when a good single-thread approach proves too slow.

Smile | :)
Luc Pattyn [My Articles] Nil Volentibus Arduum


modified 2-Mar-20 15:31pm.

AnswerRe: Igroupping with Parallel Pin
Eddy Vluggen1-Mar-20 13:47
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