Opened 10 years ago

Closed 9 years ago

Last modified 9 years ago

#10738 closed enhancement (fixed)

Background Imagery: please more aggressive caching and smarter download queening for slow connections

Reported by: RicoZ Owned by: RicoZ
Priority: major Milestone: 15.08
Component: Core imagery Version:
Keywords: cache Cc:



background imagery over slow connections is painful. Even with UMTS+, eg PCN 2012 Italy is not a great joy and much worse with EDGE or GPRS.
I am wondering if there is room for improvement?

  • josm does cache tiles - but it appears in many cases the tiles are redownloaded even if they are in cache and not yet "aged"?
  • tile downloads are apparently queued - and it seems with slow connections the queening could do smarter:
  • when zooming in/out or panning the dl queue apparently isn't discarded quickly enough and josm keeps downloading tiles which are no longer in focus?
  • when zooming there are often long delays even to redisplay tiles that were already downloaded in the same session. Perhaps a single file that needs to be downloaded blocks the display of many precached tiles? Is there some expensive cache revalidation?

Perhaps following would also help:

  • when zooming in/out or panning don't immediately start downloading tiles, then start with downloading tile under mouse or around center
  • limit downloading to fewer zoom levels, especially when zooming out.. client side scaling is much better than a black screen and long delays.

Attachments (0)

Change History (8)

comment:1 by Don-vip, 10 years ago

Component: CoreCore imagery
Keywords: cache added

comment:2 by wiktorn, 9 years ago

Milestone: 15.05
Owner: changed from team to RicoZ
Status: newneedinfo

Can you check version later than [8403]? There are some improvements in this area (better order of tiles to download, better caching). For now - only for TMS layers.

comment:3 by RicoZ, 9 years ago

Tried with PNC 2012 Italy and set an artificial bandwidth limit 24kb/s. There seems to be some improvement reusing tiles that are already on disk but when I quickly zoom out and back in an area for which background imagery was present parts of that area disappear again - probably waiting to be displayed after something else is downloaded?

There is more room for improvement when zooming in/out or when there are tiles of similar but not exactly fitting zoom factor in cache, clever rescaling could do wonders here even for much faster connections.

For zooming out it should downscale tiles in before downloading tiles of lower resolution. Similar for zooming in, rescaling tiles before downloading more detailed ones would help a lot.

comment:4 by wiktorn, 9 years ago

You mean PCN 2012 Italy? This is a WMS imagery. For now, improvements are implemented only for TMS layers. WMS improvements is planned for release at the end of July (see #11255). The way it will work for WMS will be the same, as for TMS now.

comment:5 by Don-vip, 9 years ago

Milestone: 15.0515.06

comment:6 by Don-vip, 9 years ago

Milestone: 15.0615.07

skip milestone 15.06

comment:7 by wiktorn, 9 years ago

Resolution: fixed
Status: needinfoclosed

Fixed in 8526/josm

comment:8 by Don-vip, 9 years ago

Milestone: 15.0715.08

Milestone renamed

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