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