Additional cases handled
- fix address situations where healing is not
triggered on failed writes and deletes.
- consider object exists during listing when
metadata can be successfully decoded.
In some cases a writer could be left behind unclosed, leaking compression blocks.
Always close and set compression concurrency to 2 which should be fine to keep up.
Due to https://github.com/philhofer/fwd/issues/20 when skipping a metadata entry that is >2048 bytes and the buffer is full (2048 bytes) the skip will fail with `io.ErrNoProgress`.
Enlarge the buffer so we temporarily make this much more unlikely.
If it still happens we will have to rewrite the skips to reads.
Fixes#10959
Design: https://gist.github.com/klauspost/025c09b48ed4a1293c917cecfabdf21c
Gist of improvements:
* Cross-server caching and listing will use the same data across servers and requests.
* Lists can be arbitrarily resumed at a constant speed.
* Metadata for all files scanned is stored for streaming retrieval.
* The existing bloom filters controlled by the crawler is used for validating caches.
* Concurrent requests for the same data (or parts of it) will not spawn additional walkers.
* Listing a subdirectory of an existing recursive cache will use the cache.
* All listing operations are fully streamable so the number of objects in a bucket no
longer dictates the amount of memory.
* Listings can be handled by any server within the cluster.
* Caches are cleaned up when out of date or superseded by a more recent one.
Harshavardhana