Michael Haggerty <mhagger@xxxxxxxxxxxx> writes:
> Now back to the real world. Currently, if R is changed *through* a
> symbolic reference S, then the reflogs for both R and S are updated, but
> not the reflogs for any other symbolic references that might point at R.
> If R is changed directly, then no symref's reflogs are affected, except
> for the special case that HEAD's reflog is changed if it points directly
> at R. This limitation is a hack to avoid having to walk symrefs
> backwards to find any symrefs that might be pointing at R.
Yup.
> It might actually not be extremely expensive to follow symrefs
> backwards. Symbolic references cannot be packed, so we would only have
> to scan the loose references; we could ignore packed refs. But it would
> still be a lot more expensive than just updating one file. I don't know
> that it's worth it, given that symbolic references are used so sparingly.
I personally do not think it is worth it. I further think that it
would be perfectly OK to do one of the following:
- We only maintain reflogs for $GIT_DIR/HEAD; no other symrefs
get their own reflog, and we only check $GIT_DIR/HEAD when
updating refs/heads/* and no other refs for direct reference
(i.e. HEAD -> refs/something/else -> refs/heads/master symref
chain is ignored).
- In addition to the above, we also maintain reflogs for
$GIT_DIR/refs/remotes/*/HEAD but support only when they
directly point into a remote tracking branch in the same
hierarchy. $GIT_DIR/refs/remotes/foo/HEAD that points at
$GIT_DIR/refs/remotes/bar/master is ignored and will get an
undefined behaviour.
> I think that the rule about locks as expressed above can be carried over
> the the real world:
>
> We should hold the locks on exactly those references (symbolic
> or regular) whose reflogs we plan to change. We should acquire all
> of the locks before making any changes.
Sure.
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