[tor-bugs] #15848 [Onionoo]: Update details documents in a single, atomic step

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#15848: Update details documents in a single, atomic step
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 Reporter:  karsten      |          Owner:
     Type:  enhancement  |         Status:  new
 Priority:  normal       |      Milestone:
Component:  Onionoo      |        Version:
 Keywords:               |  Actual Points:
Parent ID:               |         Points:
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 Right now, we're writing details documents in the last phase of the hourly
 updater, but one after the other.  And when we're done, we're writing the
 `relays_published` timestamp indicating which consensus these details
 documents are based on.

 [https://lists.torproject.org/pipermail/tor-dev/2015-April/008738.html
 Nusenu points out on tor-dev@] that this may create a situation when a
 details response is returned that contains details documents based on a
 later consensus than what's contained in the `relays_published` timestamp
 that is given in the response.

 Another downside of not updating all documents at once is that the sum of
 network fractions is not always exactly 100%, depending on which documents
 have already been updated.

 A possible workaround would be to include a timestamp in each details
 documents referencing the last known consensus at the time of writing the
 document.  That would fix the problem pointed out by Nusenu, but not the
 problem with fractions.  That timestamp would also be a potential source
 for confusion, because the details documents of non-running relays or
 bridges are not rewritten every hour.  Also, another workaround for
 checking whether a details document was updated recently might be to check
 whether `last_seen > relays_published || (last_seen == relays_published &&
 !running)` (untested).

 A possible real fix would be to store all documents in a database and
 update them in a single transaction.

 Not sure if there are other (simple) solutions available that don't
 require switching to a database just yet.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/15848>
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