Can conda perform an install whilst minimally updating dependencies?

Question

The conda install man page says

Conda attempts to install the newest versions of  the  requested
packages.  To  accomplish this, it may update some packages that
are already installed, or install additional packages.

So first, does this also apply to dependencies that it determines it needs to install or update? Assuming that the answer is "yes"; can that behaviour be changed? For example when working with legacy code it can be useful to update dependencies as little as possible, or install the oldest version of a dependency that will still work. Is there some way to get the conda dependency resolver to figure this out automatically, or does one have to resort to manually figuring out the dependency updates in this case?

Or maybe I am wrong entirely and this is the default behaviour? The dependency resolution rules are not clear to me from the documentation.

Answer 1

Conda's Two-Stage Solving

Conda first tries to find a version of the requested package that could be installed without changing any installed packages (a frozen solve). If that fails, it simply re-solves the entire environment from scratch with the new constraint added (a full solve). There is no in-between (e.g., minimize packages updated). Perhaps this will change in the future, but this has been the state of things for versions 4.6[?]-4.12.

Mamba

If one needs to manually work things out, I'd strongly suggest looking into Mamba. In addition to being a compiled (fast!) drop-in replacement for conda, the mamba repoquery tool could be helpful for identifying the constraints that are problematic. It has a depends subcommand for identifying dependencies and a whoneeds subcommand for reverse dependencies.

Suggested Workflow

Were I working with legacy code, I might try defining a YAML for the environment (env.yaml) and place upper bounds on crucial packages. If I needed new packages, I would dry run adding it (e.g., mamba install -d somepkg) to see how it affects the environment, figure out what if any constraint (again upper bound) it needs, add it to the YAML, then actually install it with mamba env update -f env.yaml.