On Mon, Dec 26, 2011 at 22:30, Jason Smith <j...@iriscouch.com> wrote: > On Tue, Dec 27, 2011 at 9:02 AM, Randall Leeds <randall.le...@gmail.com> > wrote: >> Awesome. I'm glad you testing descending. Sounds like "last_seq" is a >> poor name, because it applies to the particular changes request. >> >> So then we have this other thing floating around "the sequence number >> of the last replicable document change". >> Interestingly, updates to _local/<id> documents don't affect update_seq. >> >> Looking into the code, I see all the places where it's bumped >> artificially. It's quite obvious, actually. Search for "update_seq+1" >> in couch_db_updater.erl. >> >> 1) On setting _revs_limit >> 2) On setting _security >> 3) On some call to increment it (who knows why) that has an HTTP POST >> handler in couch_httpd_misc_handlers that is not exposed by >> etc/couchdb/default.ini. >> >> I don't see any reason why (1) and (2) need to be bumping this number. >> >> (3) has been there for a long time but doesn't seem to be part of the >> default public API. >> It appears to have been introduced by Damien in May of 2008 (333d18cf) >> with the commit message: >> >> Experimental functionality to increment database update seq, might >> go away, use at own risk. >> >> I propose we just get rid of all these and then update_seq becomes >> what everyone expects it to be. > > It sounds like update_seq an infallible indicator of when a backup is > necessary--better than the filesystem timestamp for the .couch file. > Just compare its value to the one from your previous backup. You'll be > sure to catch not only document updates, but also per-db configuration > settings like _security and _revs_limit. > > I'm not sure if that's 100% correct but if it is, it's useful, or at > least not useless. > > -- > Iris Couch
Thanks a ton for pointing out the operations issue of backup here; I hadn't considered it. It's worth noting, as I did before, that _local docs do not affect update_seq, though that's probably not a disaster for backup scenarios unless _local is being used by something other than the replicator. -R
