git-annex/doc/todo/CHECKPRESENT-MULTI/comment_2_87857aeaf45927846cde8cea70f9e6f4._comment
2020-02-28 15:32:50 -04:00

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[[!comment format=mdwn
username="joey"
subject="""comment 2"""
date="2020-02-28T18:58:48Z"
content="""
Export remotes don't use chunks, and use CHECKPRESENTEXPORT rather than
CHECKPRESENT. And git-annex tries to not buffer the whole worktree in
memory, but stream through it, so it can support very large worktrees.
So this idea, which I do think is a good idea, seems limited to checking
chunks.
(I'd probably want to make the chunk handling code only include up to 1
million or so chunk keys in a request, again to avoid using too much memory.
1 million chunk keys needs 160 mb ram max, 80 or less typically.)
At least for purposes of chunks, the reply to CHECKPRESENT-MULTI only needs
to say if all the keys are present. If even one chunk is missing, the object
as a whole is not present in the remote. That seems like a useful simplication.
Internally, probably Remote.checkPresent should change to taking a `[Key]`
list. Simpler than adding a whole other method for this.
Remote.External could use CHECKPRESENT when there's one key in the list,
and CHECKPRESENT-MULTI when the are multiple, falling back to CHECKPRESENT
on an UNSUPPORTED-REQUEST reply. But, I think it ought to be an
extension to the protocol, to avoid that extra roundtrip.
"""]]