todo

doc/todo/optimise_journal_access.mdwn

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+Often a command will need to read a number of files from the git-annex
+branch, and it uses getJournalFile for each to check for any journalled
+change that has not reached the branch. But typically, the journal is empty
+and in such a case, that's a lot of time spent trying to open journal files
+that DNE.
+
+Profiling eg, `git annex find --in web` shows things called by getJournalFile
+use around 5% of runtime.
+
+What if, once at startup, it checked if the journal was entirely empty.
+If so, it can remember that, and avoid reading journal files.
+Perhaps paired with staging the journal if it's not empty.
+
+This could lead to behavior changes in some cases where one command is
+writing changes and another command used to read them from the journal and
+may no longer do so. But any such behavior change is of a behavior that
+used to involve a race; the reader could just as well be ahead of the
+writer and it would have already behaved as it would after the change.
+
+But: When a process writes to the journal, it will need to update its state
+to remember it's no longer empty. --[[Joey]]