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diff --git a/docs/versioning.rst b/docs/versioning.rst new file mode 100644 index 0000000000..2f94bb6ef6 --- /dev/null +++ b/docs/versioning.rst @@ -0,0 +1,11 @@ +Versioning is, like, hard for paginating backwards because of the number of Home Servers involved. + +The way we solve this is by doing versioning as an acyclic directed graph of PDUs. For pagination purposes, this is done on a per context basis. +When we send a PDU we include all PDUs that have been received for that context that hasn't been subsequently listed in a later PDU. The trivial case is a simple list of PDUs, e.g. A <- B <- C. However, if two servers send out a PDU at the same to, both B and C would point at A - a later PDU would then list both B and C. + +Problems with opaque version strings: + - How do you do clustering without mandating that a cluster can only have one transaction in flight to a given remote home server at a time. + If you have multiple transactions sent at once, then you might drop one transaction, receive anotherwith a version that is later than the dropped transaction and which point ARGH WE LOST A TRANSACTION. + - How do you do pagination? A version string defines a point in a stream w.r.t. a single home server, not a point in the context. + +We only need to store the ends of the directed graph, we DO NOT need to do the whole one table of nodes and one of edges. |