Re: [PATCH] test thread breakage when messages are removed and re-added

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+From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>\r
+To: Notmuch Mail <notmuch@notmuchmail.org>\r
+Subject: Re: [PATCH] test thread breakage when messages are removed and\r
+ re-added\r
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+Date: Fri, 01 Apr 2016 19:27:03 -0300\r
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+--=-=-=\r
+Content-Type: text/plain\r
+\r
+On Thu 2016-03-31 14:34:53 -0300, Daniel Kahn Gillmor <dkg@fifthhorseman.net> wrote:\r
+> ghost-on-removal\r
+> ----------------\r
+>\r
+> We could unilaterally add a ghost upon message removal.  This has a\r
+> few disadvantages: the message index would leak information about what\r
+> messages the user has ever been exposed to, and we also create a\r
+> perpetually-growing dataset -- the ghosts can never be removed.\r
+>\r
+> ghost-on-removal-when-shared-thread-exists\r
+> ------------------------------------------\r
+>\r
+> We could add a ghost upon message removal iff there are other\r
+> non-ghost messages with the same thread ID.\r
+>\r
+> We'd also need to remove all ghost messages that share a thread when\r
+> the last non-ghost message in that thread is removed.\r
+>\r
+> This still has a bit of information leakage, though: the message index\r
+> would reveal that i've seen a newer message in a thread, even if i had\r
+> deleted it from my message store\r
+\r
+One more proposal along these lines:\r
+\r
+track-non-ghost-count-per-thread\r
+--------------------------------\r
+\r
+If each thread had a count of all the non-ghost messages associated with\r
+it, and that count was properly maintained by the database, then upon\r
+message deletion you would decrement the count.  when that count reached\r
+zero, you could destroy the thread.\r
+\r
+This has the same metadata leakage as\r
+ghost-on-removal-when-shared-thread-exists, but i think it might be more\r
+efficient, if we can cope with the denormalized database.\r
+\r
+This does have the downside of needing a database transition, though:\r
+we'd have to add this count to all threads in a database upgrade.\r
+\r
+\r
+\r
+What do people think of the different options?  what do you prefer?  is\r
+there some better approach that i've missed?\r
+\r
+     --dkg\r
+\r
+--=-=-=\r
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+--=-=-=--\r