Refactored the case / unicode normalization logic to be much more efficient,
and fix the last outstanding issue from #7270. Before this change, we were
doing lots of for loops and re-normalizing strings we had already normalized
earlier. Now, we leave the normalizing entirely to March and avoid
re-transforming later, which seems to make a large difference in terms of
performance.
Before this change, --resync was handled in three steps, and needed to do a lot
of unnecessary work to implement its own --ignore-existing logic, which also
caused problems with unicode normalization, in addition to being pretty slow.
After this change, it is refactored to produce the same result much more
efficiently, by reducing the three steps to two and letting ci.IgnoreExisting
do the work instead of reinventing the wheel.
The behavior and sync order remain unchanged for now -- just faster (but see
the ongoing lively discussions about potential future changes in #5681!)
Before this change, Bisync sometimes normalized NFD to NFC and sometimes
did not, causing errors in some scenarios (particularly for users of macOS).
It was similarly inconsistent in its handling of case-insensitivity.
There were three main places where Bisync should have normalized, but didn't:
1. When building the list of files that need to be transferred during --resync
2. When building the list of deltas during a non-resync
3. When comparing Path1 to Path2 during --check-sync
After this change, 1 and 3 are resolved, and bisync supports
--no-unicode-normalization and --ignore-case-sync in the same way as sync.
2 will be addressed in a future update.
Before this change, bisync needed to build a full listing for Path1, then a
full listing for Path2, then compare them -- and each of those tasks needed to
finish before the next one could start. In addition to being slow and
inefficient, it also caused real problems if a file changed between the time
bisync checked it on Path1 and the time it checked the corresponding file on
Path2.
This change solves these problems by listing both paths concurrently, using
the same March infrastructure that check and sync use to traverse two
directories in lock-step, optimized by Go's robust concurrency support.
Listings should now be much faster, and any given path is now checked
nearly-instantaneously on both sides, minimizing room for error.
Further discussion:
https://forum.rclone.org/t/bisync-bugs-and-feature-requests/37636#:~:text=4.%20Listings%20should%20alternate%20between%20paths%20to%20minimize%20errors
Before this change, bisync had no mechanism for "retrying" a file again next
time, in the event of an unexpected and possibly temporary error. After this
change, bisync is now essentially able to mark a file as needing to be
rechecked next time. Bisync does this by keeping one prior listing on hand at
all times. In a low-confidence situation, bisync can revert a given file row
back to its state at the end of the last known successful sync, ensuring that
any subsequent changes will be re-noticed on the next run.
This can potentially be helpful for a dynamically changing file system, where
files may be changing quickly while bisync is working with them.
Before this change, if there were changes to sync, bisync listed each path
twice: once before the sync and once after. The second listing caused quite
a lot of problems, in addition to making each run much slower and more
expensive. A serious side-effect was that file changes could slip through
undetected, if they happened to occur while a sync was running (between the
first and second listing snapshots.)
After this change, the second listing is eliminated by getting the underlying
sync operation to report back a list of what it changed. Not only is this more
efficient, but also much more robust to concurrent modifications. It should no
longer be necessary to avoid make changes while it's running -- bisync will
simply learn about those changes next time and handle them on the next run.
Additionally, this also makes --check-sync usable again.
For further discussion, see:
https://forum.rclone.org/t/bisync-bugs-and-feature-requests/37636#:~:text=5.%20Final%20listings%20should%20be%20created%20from%20initial%20snapshot%20%2B%20deltas%2C%20not%20full%20re%2Dscans%2C%20to%20avoid%20errors%20if%20files%20changed%20during%20sync
Before this change, bisync handled copies and deletes in separate operations.
After this change, they are combined in one sync operation, which is faster
and also allows bisync to support --track-renames and --backup-dir.
Bisync uses a --files-from filter containing only the paths bisync has
determined need to be synced. Just like in sync (but in both directions),
if a path is present on the dst but not the src, it's interpreted as a delete
rather than a copy.
This commit documents my learnings after having encountered a failure
I reported in the rclone forum[0].
I may be a fool for having failed to understand the previous
documentation, but I am likely not the only fool to get snared by it.
This commit therefore adds details to clarify what the user must do in
order to allow `--check-access` to succeed.
While at it, I've also added some basic documentation for `--check-filename`.
[0]: https://forum.rclone.org/t/bisync-check-file-check-failed/35682
