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There are two main components of a filer: directories and files.
My previous approach was to use some sequance number to generate directoryId.
However, this is not scalable. The id generation itself is a bottleneck.
It needs careful locking and deduplication checking to get a directoryId.
In a second design, each directory is deterministically mapped to UUID version 3,
which uses MD5 to map a tuple of <uuid, name> to a version 3 UUID.
However, this UUID3 approach is logically the same as storing the full path.
Storing the full path is the simplest design.
separator is a special byte, 0x00.
When writing a file:
<file parent full path, separator, file name> => fildId, file properties
For folders:
The filer breaks the directory path into folders.
for each folder:
if it is not in cache:
check whether the folder is created in the KVS, if not:
set <folder parent full path, separator, folder name> => directory properties
if no permission for the folder:
break
The filer caches the most recently used folder permissions with a TTL.
So any folder permission change needs to wait TTL interval to take effect.
When listing the directory:
prefix scan of using (the folder full path + separator) as the prefix
The downside:
1. Rename a folder will need to recursively process all sub folders and files.
2. Move a folder will need to recursively process all sub folders and files.
So these operations are not allowed if the folder is not empty.
Allowing:
1. Rename a file
2. Move a file to a different folder
3. Delete an empty folder