mutable publish sends queries to servers that have already been asked #548
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Reference: tahoe-lafs/trac-2024-07-25#548
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another problem that appeared in #546 is in the mapupdate(MODE_WRITE) code,
when run on a servermap that's already been updated once. This occurs when
the mutable file's
modify
method is used, and the first attempt failsbecause of an UncoordinatedWriteError . This triggers a retry, in which the
servermap is updated again, the (new) current version is retrieved, the
modifier function applied again, and (if anything changed) a new publish is
performed.
When this happens, the servermap is not empty: it already has a bunch of
shares from either the previous mapupdate or from the publish write requests
returning.
The mapupdate code starts by sending out N queries to the "must query"
servers: those which we already know have a share of some sort, or which
we've queried in the past. These come back, and we get a boundary map of
"1111111111". To find the real edge we must send out more queries (hoping to
get a map of 1111111111000).
The bug is that the code sends out the next batch of queries to the same
servers that it has already asked. It looks like the new queries are
determined without consulting the list of which servers to which queries have
already been sent. I think this is because those first queries were sent to
the must_query list.
my cryptic notes:
It's really bothering me that mutable file upload and download behavior is so finicky, buggy, inefficient, hard to understand, different from immutable file upload and download behavior, etc. So I'm putting a bunch of tickets into the "1.8" Milestone. I am not, however, at this time, volunteering to work on these tickets, so it might be a mistake to put them into the 1.8 Milestone, but I really hope that someone else will volunteer or that I will decide to do it myself. :-)
This appears to be an efficiency improvement and not a correctness issue.