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add remote state logs

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This allows a remote to store a piece of arbitrary state associated with a
key. This is needed to support Tahoe, where the file-cap is calculated from
the data stored in it, and used to retrieve a key later. Glacier also would
be much improved by using this.

GETSTATE and SETSTATE are added to the external special remote protocol.

Note that the state is left as-is even when a key is removed from a remote.
It's up to the remote to decide when it wants to clear the state.

The remote state log, $KEY.log.rmt, is a UUID-based log. However,
rather than using the old UUID-based log format, I created a new variant
of that format. The new varient is more space efficient (since it lacks the
"timestamp=" hack, and easier to parse (and the parser doesn't mess with
whitespace in the value), and avoids compatability cruft in the old one.

This seemed worth cleaning up for these new files, since there could be a
lot of them, while before UUID-based logs were only used for a few log
files at the top of the git-annex branch. The transition code has also
been updated to handle these new UUID-based logs.

This commit was sponsored by Daniel Hofer.
This commit is contained in:
Joey Hess 2014-01-03 16:35:57 -04:00
parent 3560fb411d
commit 3e68c1c2fd
9 changed files with 119 additions and 11 deletions
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20
doc/internals.mdwn
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@ -39,6 +39,10 @@ are added to git.
This branch operates on objects exclusively. No file names will ever
be stored in this branch.
The files stored in this branch are all designed to be auto-merged
using git's [[union merge driver|git-union-merge]]. So each line
has a timestamp, to allow the most recent information to be identified.
### `uuid.log`
Records the UUIDs of known repositories, and associates them with a
@ -110,7 +114,7 @@ somewhere else.
## `aaa/bbb/*.log`
These log files record [[location_tracking]] information
for file contents. Again these are placed in two levels of subdirectories
for file contents. These are placed in two levels of subdirectories
for hashing. See [[hashing]] for details.
The name of the key is the filename, and the content
@ -122,15 +126,23 @@ Example:
1287290776.765152s 1 e605dca6-446a-11e0-8b2a-002170d25c55
1287290767.478634s 0 26339d22-446b-11e0-9101-002170d25c55
These files are designed to be auto-merged using git's [[union merge driver|git-union-merge]].
The timestamps allow the most recent information to be identified.
## `aaa/bbb/*.log.web`
These log files record urls used by the
[[web_special_remote|special_remotes/web]]. Their format is similar
to the location tracking files, but with urls rather than UUIDs.
## `aaa/bbb/*.log.rmt`
These log files are used by remotes that need to record their own state
about keys. Each remote can store one line of data about a key, in
its own format.
Example:
1287290776.765152s e605dca6-446a-11e0-8b2a-002170d25c55 blah blah
1287290767.478634s 26339d22-446b-11e0-9101-002170d25c55 foo=bar
## `schedule.log`
Used to record scheduled events, such as periodic fscks.