Ticket Q267890

Only Visible to You and DevExpress Support

Visible to All Users

Modify support ticket and change its visibility

Urgent Duplicate

We have closed this ticket because another page addresses its subject:

Working with TcxCustomDataController in separate thread

cxGrid and Async Fetch

BH BH

Bernhard Hartl Bernhard Hartl

created 15 years ago (modified 15 years ago)

Is it still impossible/dangerous to use AsyncFetch with Async Fetch Enabled???
I know about http://www.devexpress.com/Support/Center/p/DQ7728.aspx
and http://www.devexpress.com/Support/Center/p/CB41565.aspx
Are there Limitations when using the grid just for displaying data
most of the SQL-tables that have got a very high count of rows are only needed for viewing
so it would be a great option to be able to enable AsyncFetch for a ReadOnly cxGrid
thenk you
Bernhard Hartl

Show previous comments (0) Comments (0)

Answers

DevExpress Support Team DevExpress Support Team

created 15 years ago (modified 15 years ago)

Hello Bernhard.
Thank you for your message.
Unfortunately, this limitation still persists due to architectural peculiarities of our components. However, we have a corresponding suggestion in our Support Center. Please refer to the Working with TcxCustomDataController in separate thread report for additional information. You can start tracking this issue to stay informed on our progress with it.
Best regards,
Ingvar.

Show previous comments (5) Comments (8)

RB RB

Private Ramon Bachmeier Private Ramon Bachmeier 7 years ago

Hello Ingvar

Now 8 Years are gone
We are using Delphi 10 Tokyo

Is it still impossible/dangerous to use AsyncFetch with Async Fetch Enabled???

thank you

Bernhard

Private DevExpress Support Team Private DevExpress Support Team 7 years ago

Hello Bernhard,

Our grid control's DataController is still populated with data in a single thread. However, now some operations (filtering, sorting) can be performed in secondary threads. Please review the "Multi-Threaded Data Processing" help topic for details.

In addition, I suggest that you take a look at the "Server Mode" help topic. This mode significantly increases the grid control's speed since most data operations are performed at a server level.

RB RB

Private Ramon Bachmeier Private Ramon Bachmeier 7 years ago

Hello Paulo

"Server Mode" does disable many many features of the grid that are neccersarry for our users - that is not a valid option to me
do you see a way to use the CPU-Time better than just displaying a hourglass and wait until the the AdoDataset releases from it's blocked state?!?!?
That freezes the GUI while waiting for SQL-Server and the data to arrive…
Best would be a possibility how to start feeding the Grid while the dataset is populated by the SQL-Server
That would especially be very useful when dealing with 10,000 or more datasets and I simply want to refresh the data to the current state

Am dealing with a database in the chemical industry where all alarms and messages from a big plant (15,000workers) are feeded into the MS-SQL-Database. And the cxGrid is the Frontend. We did build many things around cxGrid to make all that usable. But the main unattractiveness of the application is still the blocked GUI while waiting for TAdoDataset to be reactive again
The only possibility I know is to use a TMemDataset for Grid and use a TAdoDataset in the backgroundthread - and copy the data from AdoDataset to MemDataset when SQL has finished …

Do you see any other alternative but to copy Data to MemDataset???

Thank you

Bernhard Hartl, from Austria

Private DevExpress Support Team Private DevExpress Support Team 7 years ago

While copying data to an in-memory data set is suitable in this scenario, I think that the use of Server Mode may work better here. From what I gather, you mean copying only a small part of data records from the TAdoDataset component. In fact, that is what our Grid Mode does. Correct sorting, filtering, and grouping are not available in this case because DataController knows nothing about these records that are not copied.

Would you elaborate on the grid's features Server Mode prevents you from using? This information may help us improve this mode.

RB RB

Private Ramon Bachmeier Private Ramon Bachmeier 7 years ago

Hello Paolo

ServerMode does not work at all - as it breaks my UserInterface

The scenario is - I get about 2Million Datasets into my Database every day.
There are all datasets (alarms, warnings, …) in the database from 2003 until now.
That means it is a database with a lot of content.
And the people who want to search through that data are not aware of SQL
That is why I came up with the Idea 12Years ago to use your Grid and it's easy to use your cxGrid filters
to enable the users to create WHERE-Statements in an intuitive way,
Save that Filter from Grid-Filter to a SQL-Filter
Join several Filters
until they got in the grid what they want to see
and enable them to link actions to that Filters
For example send a eMail when a Alarm goes through their Filter
In the background there is the SQLParser (http://www.sqlparser.com/) and a self written PCode Machine working to serve all that

when the WHERE-Statement is to general and I would receive more than 25,000 datasets (would crash cxGrid)
I pull the break by fetching only the TOP 25,000 datasets

What I thought 8Years ago - and now again - is how to enhance the user experience while updating the content of the grid

there are for example 20,000 datasets in the grid-Datacontroller
and I have to update it
that takes currently half a second - for the SQL to execute - until it is visible in the cxGrid

but everything that can happen to the datasets is that new datasets are added

that means I will change the GUI
- connect Grid to a MemDataset
- move the AdoDataset to a seperate Worker-Thread
- the Worker-Thread will have got a ID-List that knows all ID's that are currently in the MemDataset
- when the Worker-Thread fetches the first datasets from SQL-Server it compares their ID's to the ID-List and sends all NEW Datasets to a ThreadSaveQueue
- the GUI main thread will receive that datasets from the ThreadSaveQueue and add the new datasets to the MemDataset

that way the user will have got a much smoother GUI for further analyzing the data

and when User changes the SQL-WHERE-Filter or Selected-Columns
I will purge the old Cache (MemDataset, ID-List)
and fill it with the new content - when the WorkerThread does fetch the first datasets from SQL-Server

I will implement it this way

thank you

Bernhard

Private DevExpress Support Team Private DevExpress Support Team 7 years ago

Thank you for your clarification. It seems that in your scenario this is indeed the best approach.
As an alternative solution to visually lock the UI, you can try the TcxGrid.LockedStateImageOptions properties set. In combination with the BeginUpdate and EndUpdate methods these properties can produce some visual effects to inform an end-user that update is in progress.

RB RB

Private Ramon Bachmeier Private Ramon Bachmeier 7 years ago

Hello Paulo

I did create the Async Refresh that way - it works fine
but there is one problem…

when the MemDataset is modified - cxGrid.Datacontroller stalls the main thread for several seconds

To hide that MemDataset Update from the user I have to use

MemDataset.DisableControls;
UpdateMemDataset;
MemDataset.EnableControls;

cxGridView.BeginUpdate;
UpdateMemDataset;
cxGridView.EndUpdate;

MemDataset.EnableControls or cxGridView.EndUpdate causes cxGrid.Datacontroller to stall the main thread for several seconds

is there any way to avoid that stall???

Ideas:
is there any way to decouple GridView from the DataController
Update the DataContoller in the Background-Thread
and couple GridView again to the datacontroller

or to clone the Datacontroller
Update the cloned DataContoller in the Background-Thread
couple GridView to the cloned datacontroller
Free the old Datacontroller

or something like that

I am simply searching for a way - how to update the datacontroller in the background to minimize the stall-time of the main thread as much as possible

Thank you

Bernhard Hartl

Private DevExpress Support Team Private DevExpress Support Team 7 years ago

Hello Bernhard,

Our Data Controller does not support this functionality. Theoretically, you can directly access its inner storage (the protected DataStorage property) and its records by using their pointers from a secondary thread. However, this approach is not tested and I suggest that you carefully test results before using it. In fact, we already have a special helper class to perform this access. However, we do this in the main thread (see the cxDBTL.pas unit). If you decide to try this approach, take a look at the TcxDataStorageHelper class in the cxDataStorage.pas unit.
I hope this information will be of help.

Created: July 23, 2010 10:15 AM

Modified: August 10, 2018 7:52 AM

Platform: VCL

Product: ExpressQuantumGrid Suite

Build: 6.0.52

IDE: Borland Delphi 7

Related Tickets

Disclaimer: The information provided on DevExpress.com and affiliated web properties (including the DevExpress Support Center) is provided "as is" without warranty of any kind. Developer Express Inc disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. Please refer to the DevExpress.com Website Terms of Use for more information in this regard.

Confidential Information: Developer Express Inc does not wish to receive, will not act to procure, nor will it solicit, confidential or proprietary materials and information from you through the DevExpress Support Center or its web properties. Any and all materials or information divulged during chats, email communications, online discussions, Support Center tickets, or made available to Developer Express Inc in any manner will be deemed NOT to be confidential by Developer Express Inc. Please refer to the DevExpress.com Website Terms of Use for more information in this regard.

cxGrid and Async Fetch

Answers

Recently viewed tickets