Change storage schema

[remram44]

The current storage scheme has the following problems:

• (C) Collisions: different entries (= sets of metadata) with the same content won't be accepted (issue Same file, different metadata #10)
• (F) File name selection: Matthias wants filenames to be selectable (or changeable)

Other options that come to mind are:

• (M) Changing metadata for an entry
• (D) Deduplication (store files once if two entries have the same content)

The schemas I have in mind are:

1

hash(content) <-> filename
               -> metadata

• can rename file
• can add/change metadata
• two files with the same hash will share metadata

2

hash(content||metadata) <-> filename
                         -> metadata

• can rename file
• can't change metadata
• no collisions
• no deduplication

3

uuid <-> filename
      -> metadata

• can rename file
• can change metadata
• no collisions
• no deduplication

4

uuid -> hash(content) <-> filename
     -> metadata

• can rename file (affects multiple entries)
• can change metadata
• no collisions
• deduplication

5

hash(content||metadata) -> hash(content) <-> filename
                        -> metadata

• can rename file (affects multiple entries)
• can't change metadata
• no collisions
• deduplication

6

hash(content||metadata) <-> filename
                         -> metadata

• can rename file
• can't change metadata
• no collisions
• no deduplication

Right now:

Legacy

hash(content) = filename
              -> metadata

• can't rename file
• can change metadata (not implemented)
• collisions possible

[remram44]

Master now uses (since d003bce):

hash(content||metadata) -> hash(content) = filename
                        -> metadata

• can't rename file (but can be added)
• can't change metadata (without creating new objectid)
• no collisions
• deduplication