Guriddo » Topic: virtual scrolling – pages sometimes not displayed (when scrolling using the slider)

virtual scrolling – pages sometimes not displayed (when scrolling using the slider)

Guriddo
virtual scrolling – pages sometimes not displayed (when scrolling using the slider)

This topic has 14 replies, 3 voices, and was last updated 14 years, 8 months ago by OlegK.

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August 23, 2011 at 7:55 pm #78913

de
Participant

Hi,

We're planning to use jqGrid.

As we're planning to use it over thousands of entries one requirement is to use virtual scrolling, over dynamically loaded date.

This seems to be fine when just loading page by page. But when using the slider a lot of requests may be issues and eventually the page may not actually appear – only when paging up/down everything is displayed again.

This happens in Firefox and IE the same.

I can't reproduce this using your demo page. I pressume this is because loadonce is set to true and it doesn't actually go to the server again.

Is this a known issue?

Thank you for your help

D.
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Viewing 14 replies - 1 through 14 (of 14 total)

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August 26, 2011 at 4:23 pm #98698

de
Participant

I believe I identified the issue. It seems it can be best reproduced by just pressing the mouse down on the scrollbar for a while (so that it will issue multiple requests in a short time). Sometimes an older request may take a little longer and arrives after a more recent page request.

The issue didn't occure anymore after I amended the populate function (in grid.base.js) to remember the page number at request time and then compare it with the page number requested last before processing the result (ajax success).

e.g.:

var pageNo = ts.p.postData.page;

August 29, 2011 at 6:22 pm #98708

kobruleht
Participant

I hold mouse down for 30 seconds in scrollbar for 10000 rows table, page size is 80 but could not reproduce the issue. I used settings:

August 30, 2011 at 1:51 pm #98723

de
Participant

Thank you for your response.

In my example I've set rowNum to 10 which will make multiple concurrent requests more likely (we'll increase rowNum eventually). So with a rowNum of 80 it might be more likely to happen by moving the scrollbar around randomly.
Ultimately you'll have to get the server to take longer to respond for one of the requests though to be able to reproduce the issue.

While I was debugging it I added logging and got the following results:
GET http://…/?…0&page=19&…

August 30, 2011 at 2:33 pm #98724

kobruleht
Participant

I changed page size to 10 and added

August 30, 2011 at 6:28 pm #98726

de
Participant

Thank you for reproducing the issue.

I should have mentioned that I configured the height of the grid to be still less than 10 rows. i.e. 10 rows should fill a page.

I wasn't sure whether my fix would work for page boundaries although I couldn't produce any issue with it. I don't know why it would be blank though.

(The patch seem to be applied correctly)

If you're setup is public I'd be happy to have a look myself as well.

(Of course, I'd be more than open for any other kind of fix)

August 30, 2011 at 7:03 pm #98727

kobruleht
Participant

It seems that

August 31, 2011 at 1:01 pm #98730

de
Participant

I managed to add the pull request (change id: I15fa3b5b9269403262eb5c9fa3b62122ae6158e6).

I also followed your suggestion to use npage which seem to work fine (it does always appear to be requesting 2 pages).

August 31, 2011 at 1:14 pm #98732

kobruleht
Participant

You should be aware that npage option as serious bug as descibed in

http://stackoverflow.com/questions/7231975/how-to-avoid-duplicate-rows-if-npage-protocol-extension-is-used-in-jqgrid

and in bugs forum here. those occurs even

September 5, 2011 at 4:41 pm #98750

de
Participant

Thank you for pointing this out.

The other issue seems to have different cause. I'd suggest to keep them separate.

(I don't think our users will use ctrl+end)

Perhaps a workaround to the other problem is to ignore the page if it is the same as the last one. But it would be better to prevent that before requesting the page.

September 5, 2011 at 4:46 pm #98751

kobruleht
Participant

This issue occurs without ctrl+end also: if scrolled by scrollbar or editing starts.

September 5, 2011 at 7:22 pm #98752

de
Participant

But the problem only occures in combination with the npage extension?

If so, then it would suggest that the problem isn't that it is processing old responses after more recent ones.

i.e. it would either be an issue with the actual request being generated or when it's processing the response (e.g. it may request overlapping pages and when processing the response it may not handle that correctly at assumes that the response needs to be appended in full)

(Unofrtunately I won't have the time to debug that issue right now)

September 5, 2011 at 7:34 pm #98753

kobruleht
Participant

If npage: parameter is removed, this issue does not occur.

September 12, 2011 at 2:17 pm #98787

kobruleht
Participant

If rowNum: 50 is used, pressing Ctrl+End in 10252 rows table retrieves pages 205,206,181,182,205,206,181,182,.. etc forever.

jqGrid enters into infinite loop.

Aslo maybe commit https://github.com/tonytomov/jqGrid/commit/e24a7ecdbd830b00e30ad2785045af1fe366ce09

September 12, 2011 at 4:00 pm #98788

OlegK
Participant

Hello Andrus,

If you quote me, please, do it correct. I wrote you: “I don't use virtual scrolling myself. …
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