Contributed by Steve Loughran.
This patch avoids issuing any HEAD path request when creating a file with overwrite=true,
so 404s will not end up in the S3 load balancers unless someone calls getFileStatus/exists/isFile
in their own code.
The Hadoop FsShell CommandWithDestination class is modified to not register uncreated files
for deleteOnExit(), because that calls exists() and so can place the 404 in the cache, even
after S3A is patched to not do it itself.
Because S3Guard knows when a file should be present, it adds a special FileNotFound retry policy
independently configurable from other retry policies; it is also exponential, but with
different parameters. This is because every HEAD request will refresh any 404 cached in
the S3 Load Balancers. It's not enough to retry: we have to have a suitable gap between
attempts to (hopefully) ensure any cached entry wil be gone.
The options and values are:
fs.s3a.s3guard.consistency.retry.interval: 2s
fs.s3a.s3guard.consistency.retry.limit: 7
The S3A copy() method used during rename() raises a RemoteFileChangedException which is not caught
so not downgraded to false. Thus: when a rename is unrecoverable, this fact is propagated.
Copy operations without S3Guard lack the confidence that the file exists, so don't retry the same way:
it will fail fast with a different error message. However, because create(path, overwrite=false) no
longer does HEAD path, we can at least be confident that S3A itself is not creating those cached
404 markers.
Change-Id: Ia7807faad8b9a8546836cb19f816cccf17cca26d
9221704f85