Bug#208201: acknowledged by developer (Re: Bug#208201: apt: when upgrading, wrong occupied space is shown)
>> Sorry for not reporting exact numbers, but that was a thing that I
>> noticed only after the installation process was finished.
>
>apt and any other tool will always be incorrect when trying to estimate
>the amount of diskpace that will be used for a package. While the
>differences you got are large, they are nog totally unexpected when
>dealing with packages with a large number of files.
No, I don't think that this is an explanation for the behaviour I
observed. I'd reopen this bug report.
I'll try to rephrase my bug report to make it clearer.
Before installing, I did a quick approximate computation of the space
that I was going to need, by algebraically summing the Installed-Size
numbers. It turned out that the size of the new packages was around 40
MB, while the size of the packages to be removed was around 20 MB.
apt told me that it was going to occupy around 40 MB.
After the installation, I observed that the free space was reduced by
about 20 MB.
The easiest explanation is that apt did not take in account the packages
to be removed.
What does apt do when it computes the total occupancy? I suppose that
it simply does an algebraical sum of the contents of the Installed-Size
fields. If this is the case, then there must be a bug somewhere, I find
it difficult to ascribe this behaviour to a problem of inaccuracy.
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