The reason to use removeBeforeRemoteEndTime is twofold.
First, removeBefore sends two protocol commands. Currently, the HTTP
protocol runner only supports sending a single command per invocation.
Secondly, the http server gets a monotonic timestamp from the client. So
translating back to a POSIXTime would be annoying.
The timestamp flow with a proxy will be:
- client gets timestamp, which gets the monotonic timestamp from the
proxied remote via the proxy. The timestamp is currently not
proxied when there is a single proxy.
- client calls remove-before
- http server calls removeBeforeRemoteEndTime which sends REMOVE-BEFORE
to the proxied remote.
Websockets would work, but the problem with using them for this is that
each lockcontent call is a separate websocket connection. And that's an
actual TCP connection. One TCP connection per file dropped would be too
expensive. With http long polling, regular http pipelining can be used,
so it will reuse a TCP connection.
Unfortunately, at least with servant, bi-directional streams with long
polling don't result in true bidirectional full duplex communication.
Servant processes the whole client body stream before generating the server
body stream. I think it's entirely possible to do full bi-directional
communication over http, but it would need changes to servant.
And, there's no way for the client to tell if the server successfully
locked the content, since the server will keep processing the client
stream no matter what.:
So, added a new api endpoint, keeplocked. lockcontent will lock the key
for 10 minutes with retention lock, and then a call to keeplocked will
keep it locked for as long as needed. This does mean that there will
need to be a Map of locks by key, and I will probably want to add
some kind of lock identifier that lockcontent returns.
For clusters, the timestamps have to be translated, since each node can
have its own idea about what time it is. To translate a timestamp, the
proxy remembers what time it asked the node for a timestamp in
GETTIMESTAMP, and applies the delta as an offset in REMOVE-BEFORE.
This does mean that a remove from a cluster has to call GETTIMESTAMP on
every node before dropping from nodes. Not very efficient. Although
currently it tries to drop from every single node anyway, which is also
not very efficient.
I thought about caching the GETTIMESTAMP from the nodes on the first
call. That would improve efficiency. But, since monotonic clocks on
!Linux don't advance when the computer is suspended, consider what might
happen if one node was suspended for a while, then came back. Its
monotonic timestamp would end up behind where the proxying expects it to
be. Would that result in removing when it shouldn't, or refusing to
remove when it should? Have not thought it through. Either way, a
cluster behaving strangly for an extended period of time because one
of its nodes was briefly asleep doesn't seem like good behavior.
Added Maybe POSIXTime to SafeDropProof, which gets set when the proof is
based on a LockedCopy. If there are several LockedCopies, it uses the
closest expiry time. That is not optimal, it may be that the proof
expires based on one LockedCopy but another one has not expired. But
that seems unlikely to really happen, and anyway the user can just
re-run a drop if it fails due to expiry.
Pass the SafeDropProof to removeKey, which is responsible for checking
it for expiry in situations where that could be a problem. Which really
only means in Remote.Git.
Made Remote.Git check expiry when dropping from a local remote.
Checking expiry when dropping from a P2P remote is not yet implemented.
P2P.Protocol.remove has SafeDropProof plumbed through to it for that
purpose.
Fixing the remaining 2 build warnings should complete this work.
Note that the use of a POSIXTime here means that if the clock gets set
forward while git-annex is in the middle of a drop, it may say that
dropping took too long. That seems ok. Less ok is that if the clock gets
turned back a sufficient amount (eg 5 minutes), proof expiry won't be
noticed. It might be better to use the Monotonic clock, but that doesn't
advance when a laptop is suspended, and while there is the linux
Boottime clock, that is not available on other systems. Perhaps a
combination of POSIXTime and the Monotonic clock could detect laptop
suspension and also detect clock being turned back?
There is a potential future flag day where
p2pDefaultLockContentRetentionDuration is not assumed, but is probed
using the P2P protocol, and peers that don't support it can no longer
produce a LockedCopy. Until that happens, when git-annex is
communicating with older peers there is a risk of data loss when
a ssh connection closes during LOCKCONTENT.
This allows lockContentShared to lock content for eg, 10 minutes and
if the process then gets terminated before it can unlock, the content
will remain locked for that amount of time.
The Windows implementation is not yet tested.
In P2P.Annex, a duration of 10 minutes is used. This way, when p2pstdio
or remotedaemon is serving the P2P protocol, and is asked to
LOCKCONTENT, and that process gets killed, the content will not be
subject to deletion. This is not a perfect solution to
doc/todo/P2P_locking_connection_drop_safety.mdwn yet, but it gets most
of the way there, without needing any P2P protocol changes.
This is only done in v10 and higher repositories (or on Windows). It
might be possible to backport it to v8 or earlier, but it would
complicate locking even further, and without a separate lock file, might
be hard. I think that by the time this fix reaches a given user, they
will probably have been running git-annex 10.x long enough that their v8
repositories will have upgraded to v10 after the 1 year wait. And it's
not as if git-annex hasn't already been subject to this problem (though
I have not heard of any data loss caused by it) for 6 years already, so
waiting another fraction of a year on top of however long it takes this
fix to reach users is unlikely to be a problem.
This will allow having an internal thread speaking P2P protocol,
which will be needed to support proxying to external special remotes.
No serialization is done on the internal P2P protocol of course.
When a ByteString is being exchanged, it may or may not be exactly
the length indicated by DATA. While that has to be carefully managed
for the serialized P2P protocol, here it would require buffering the
whole lazy bytestring in memory to check its length when sending,
so it's better to do length checks on the receiving side.
Before it was using a node that might have had a higher cost.
Also threw in a random selection from amoung the low cost nodes. Of
course this is a poor excuse for load balancing, but it's better than
nothing. Most of the time...
Walking a tightrope between security and convenience here, because
git-annex-shell needs to only proxy for things when there has been
an explicit, local action to configure them.
In this case, the user has to have run `git-annex extendcluster`,
which now sets annex-cluster-gateway on the remote.
Note that any repositories that the gateway is recorded to
proxy for will be proxied onward. This is not limited to cluster nodes,
because checking the node log would not add any security; someone could
add any uuid to it. The gateway of course then does its own
checking to determine if it will allow proxying for the remote.
When there are multiple gateways to a cluster, this sets up proxying
for nodes that are accessed via a remote gateway.
Eg, when running in nyc and amsterdam is the remote gateway,
and it has node1 and node2, this sets up proxying for
amsterdam-node1 and amsterdam-node2. A client that has nyc as a remote
will see proxied remotes nyc-amsterdam-node1 and nyc-amsterdam-node2.
Just look at the existing proxied remotes that correspond to already
existing nodes of the cluster, and keep those nodes in the cluster.
While adding any remotes of the local repo that are configured as
cluster nodes. This allows removing cluster nodes from the local repo
and updating, without it also removing nodes provided by other gateways.
This makes git-annex sync and similar not treat proxied remotes as git
syncable remotes.
Also, display in git-annex info remote when the remote is proxied.
When the destination does not start with a copy, the cluster has one or
more copies. If more, dropping would reduce the number of copies, so
numcopies must be checked.
Considered checking how many nodes of the cluster contain a copy. If
only 1 node does, it could allow a move without checking numcopies.
The problem with that, though, is that other nodes of the cluster could
have copies that we don't know about. And dropping from a cluster tries
to drop from all nodes, so will drop even from those. So any drop from a
cluster can remove more than 1 copy.
Dropping from a cluster drops from every node of the cluster.
Including nodes that the cluster does not think have the content.
This is different from GET and CHECKPRESENT, which do trust the
cluster's location log. The difference is that removing from a cluster
should make 100% the content is gone from every node. So doing extra
work is ok. Compare with CHECKPRESENT where checking every node could
make it very expensive, and the worst that can happen in a false
negative is extra work being done.
Extended the P2P protocol with FAILURE-PLUS to handle the case where a
drop from one node succeeds, but a drop from another node fails. In that
case the entire cluster drop has failed.
Note that SUCCESS-PLUS is returned when dropping from a proxied remote
that is not a cluster, when the protocol version supports it. This is
because P2P.Proxy does not know when it's proxying for a single node
cluster vs for a remote that is not a cluster.
Client side support for SUCCESS-PLUS and ALREADY-HAVE-PLUS
is complete, when a PUT stores to additional repositories
than the expected on, the location log is updated with the
additional UUIDs that contain the content.
Started implementing PUT fanout to multiple remotes for clusters.
It is untested, and I fear fencepost errors in the relative
offset calculations. And it is missing proxying for the protocol
after DATA.
Support selecting what remote to proxy for each top-level P2P protocol
message.
This only needs to be extended now to support fanout to multiple
nodes for PUT and REMOVE, and with a remote that fails for
LOCKCONTENT and UNLOCKCONTENT.
But a good first step would be to implement CHECKPRESENT and GET for
clusters. Both should select a node that actually does have the content.
That will allow a cluster to work for GET even when location tracking is
out of date.
Works down to P2P protocol.
The question now is, how to handle protocol version negotiation for
clusters? Connecting to each node to find their protocol versions and
using the lowest would be too expensive with a lot of nodes. So it seems
that the cluster needs to pick its own protocol version to use with the
client.
Then it can either negotiate that same version with the nodes when
it comes time to use them, or it can translate between multiple protocol
versions. That seems complicated. Thinking it would be ok to refuse to
use a node if it is not able to negotiate the same protocol version with
it as with the client. That will mean that sometimes need nodes to be
upgraded when upgrading the cluster's proxy. But protocol versions
rarely change.
For eg, upload fanout.
Delay connecting to a remote until it's needed. When there are many
proxied remotes, it would not do for the proxy to connect to each of
them on startup; that could take a long time.
Handled limitCopies, as well as everything using fromNumCopies and
fromMinCopies.
This should be everything, probably.
Note that, git-annex info displays a count of repositories, which still
includes cluster. I think that's ok. It would be possible to filter out
clusters there, but to the user they're pretty much just another
repository. The numcopies displayed by eg `git-annex info .` does not
include clusters.
This is to avoid inserting a cluster uuid into the location log when
only dead nodes in the cluster contain the content of a key.
One reason why this is necessary is Remote.keyLocations, which excludes
dead repositories from the list. But there are probably many more.
Implementing this was challenging, because Logs.Location importing
Logs.Cluster which imports Logs.Trust which imports Remote.List resulted
in an import cycle through several other modules.
Resorted to making Logs.Location not import Logs.Cluster, and instead
it assumes that Annex.clusters gets populated when necessary before it's
called.
That's done in Annex.Startup, which is run by the git-annex command
(but not other commands) at early startup in initialized repos. Or,
is run after initialization.
Note that is Remote.Git, it is unable to import Annex.Startup, because
Remote.Git importing Logs.Cluster leads the the same import cycle.
So ensureInitialized is not passed annexStartup in there.
Other commands, like git-annex-shell currently don't run annexStartup
either.
So there are cases where Logs.Location will not see clusters. So it won't add
any cluster UUIDs when loading the log. That's ok, the only reason to do
that is to make display of where objects are located include clusters,
and to make commands like git-annex get --from treat keys as being located
in a cluster. git-annex-shell certainly does not do anything like that,
and I'm pretty sure Remote.Git (and callers to Remote.Git.onLocalRepo)
don't either.
Since the cluster UUID is inserted into the location log when the
location log lists a node as containing content.
Also avoid trying to lock content on cluster remotes. The cluster nodes
are also proxied, so that content can be locked on individual nodes, and
locking content on a cluster as a whole probably won't be implemented.
And made git-annex whereis use numcopies machinery for displaying its
count, so it won't count cluster UUIDs redundantly to nodes.
Other commands, like git-annex info that also display numcopies
information already used the numcopies machinery.
There is more to be done, fromNumCopies is sometimes used to get a
number that is compared with a list of UUIDs. And limitCopies doesn't
use numcopies machinery.
When imported along with Logs.Location, it can be an unused import and
it won't warn, due to reexports. The point if this is really to show
that Logs.Presence is not widely used, outside Logs/
One benefit of this is that a typo in annex-cluster-node config won't
init a new cluster.
Also it gets the cluster description set and is consistent with
initremote.
