Re: More ideas about logging.

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+From: Ethan Glasser-Camp <ethan.glasser.camp@gmail.com>\r
+To: Austin Clements <amdragon@MIT.EDU>, David Bremner <bremner@debian.org>\r
+Subject: Re: More ideas about logging.\r
+In-Reply-To: <20111216040722.GC12245@mit.edu>\r
+References: <87obv9i7y3.fsf@zancas.localnet> <20111216040722.GC12245@mit.edu>\r
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+Date: Fri, 12 Oct 2012 12:28:36 -0400\r
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+Cc: Olly Betts <olly@survex.com>, Notmuch Mail <notmuch@notmuchmail.org>\r
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+\r
+Austin Clements <amdragon@MIT.EDU> writes:\r
+\r
+> The trouble with this approach is that the OS doesn't have to flush\r
+> logfile to the disk platters in any particular order relative to the\r
+> updates to Xapian.  So, after someone trips over your plug, you could\r
+> come back with Xapian saying you have 500 log entries when your\r
+> logfile comes back with only 20.  The only way I know of to fix this\r
+> is to fsync after the logfile write, which would obviously have\r
+> performance issues.  But maybe there are cleverer ways?\r
+\r
+Sorry to jump in almost a year after the fact, but..\r
+\r
+How bad do you think those performance issues are going to be? I don't\r
+see them as prohibitive, even in the case where you write a log entry\r
+for every message being tagged. Xapian's doing an fsync each time we\r
+commit, isn't it? (Or is there some cute trick where it rename()s the\r
+database?)\r
+\r
+If, instead of truncating, you replay logged operations, I think you can\r
+get away with just writing log entries for user-level operations (like\r
+"notmuch tag +mytag to:somequery") which could touch a lot of\r
+messages. This would then only require one fsync on the log file before\r
+doing a lot of tag updates.\r
+\r
+Ethan\r