[Bug 438870] Re: Downloads should start when the previous one ends

[Matthew Paul Thomas]

You're probably right that downloading for more than one transaction at
a time wouldn't be worth it. (It might save time if the downloads were
from different servers, because some of the latency might be at the
server's end rather than the client's. But in our case they will mostly
be from the same server.) So let's concentrate on downloading for only
one transaction at a time.

How much time that would save would depend mainly on four things.

First, on how what proportion of the average installation time is taken
up by the download, and in particular, how close that average is to 50%.
(The further away it is from 50%, in *either* direction, the more often
there will be slack where only one task is in progress rather than two.)

Second, on how much variation there is in that average proportion. (Even
if the average is exactly 50%, if it varies a lot, there will still be
lots of slack.)

Third, on the length of the average queue: how often there's an X+1 at
all, and an X+2 to take up any slack from the X+1 download finishing
before X finishes, and an X+3 etc.

And fourth, how much the process of downloading X+1, and writing that
downloaded file to disk, slows down the process of installing X. (Maybe
this is negligible.)

As far as I know, we don't have data on any of these at the moment. I
expect it would be fairly easy to write a script to measure the first
two at least: choose a random package, time its download, time its
installation, uninstall, repeat. And measuring those first two would be
useful by itself, because it would help us make the existing progress
bar smoother. <https://wiki.ubuntu.com/SoftwareCenter/SmoothProgress>

As for presenting progress of downloading packages that you thought
would be downloaded already, a basic way to handle that would be:
estimate/measure how often it happens, estimate/measure what proportion
of the total time it takes when it does happen, multiply those two
together, and allocate the resulting proportion of the total progress
bar to it.

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https://bugs.launchpad.net/bugs/438870

Title:
  Downloads should start when the previous one ends

Status in “aptdaemon” package in Ubuntu:
  Confirmed
Status in “software-center” package in Ubuntu:
  Confirmed

Bug description:
  I was installing a few programs at once. When one of the programs was finished downloading it continued on to install the program. When that program finished it went on to download and install the next one and then went on to the next one after that.
  It would save a lot of time if when the program is installing to start the download of the next.

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