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REMOVE-BEFORE and GETTIMESTAMP proxying

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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.
This commit is contained in:
Joey Hess 2024-07-04 15:08:33 -04:00
parent 99b7a0cfe9
commit f452bd448a
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4 changed files with 97 additions and 5 deletions
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4
Annex/Cluster.hs
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@ -67,7 +67,8 @@ proxyCluster clusteruuid proxydone servermode clientside protoerrhandler = do
(selectnode, closenodes) <- clusterProxySelector clusteruuid
protocolversion bypassuuids
concurrencyconfig <- getConcurrencyConfig
proxy proxydone proxymethods servermode clientside
proxystate <- liftIO mkProxyState
proxy proxydone proxymethods proxystate servermode clientside
(fromClusterUUID clusteruuid)
selectnode concurrencyconfig protocolversion
othermsg (protoerrhandler closenodes)
@ -107,6 +108,7 @@ clusterProxySelector clusteruuid protocolversion (Bypass bypass) = do
-- could be out of date, actually try to remove from every
-- node.
, proxyREMOVE = const (pure nodes)
, proxyGETTIMESTAMP = pure nodes
-- Content is not locked on the cluster as a whole,
-- instead it can be locked on individual nodes that are
-- proxied to the client.