[yocto] Why did my build need to redo so many tasks?

[Gary Thomas]

Yesterday, I built a large image using Poky/Yocto 870323cac1e
Today I updated my Poky repo to 231d4a9d3

When I rebuilt the same image, bitbake kicked off more than
5200 tasks, building virtually every package from scratch.

How can I tell why this happened?  I don't have buildhistory
enabled, but I do still have the tmp & sstate-cache trees
from the process.  Is there enough info laying around that
I can tell, e.g. why the GCC toolchain had to be rebuilt
completely?

Am I correct in assuming that bitbake-whatchanged is really
a Quija board and can only tell me [in advance] what will need
to be done if my layers change?  When I ran it after the long
build above, it didn't really tell me much :-(

-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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