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+Date: Thu, 21 Aug 2014 10:59:11 +0200\r
+From: Gaute Hope <eg@gaute.vetsj.com>\r
+Subject: Re: DatabaseModifiedErrors causing troubles\r
+To: notmuch@notmuchmail.org\r
+References:\r
+ <CABKe4MvEdcsq8BZ-vq6R0Vnw87zEgBvqW_2F-Wysf5GNchqweg@mail.gmail.com>\r
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+\r
+Gaute Hope <eg@gaute.vetsj.com> wrote on Mon, 11 Aug 2014 14:17:54 +0200:\r
+> Hi,\r
+>\r
+> I've been working on an application that keeps a read-only handle on\r
+> the notmuch database open for a long time. In some cases when a new\r
+> message is added along with some renames of other messages using\r
+> 'notmuch new' while the application is running I get an Xapian\r
+> exception: DatabaseModifiedError:\r
+>\r
+> A Xapian exception occurred performing query: The revision being\r
+> read has been discarded - you\r
+> should call Xapian::Database::reopen() and retry the operation.\r
+>\r
+> Which seems to be printed from: notmuch_query_search_threads ->\r
+> notmuch_query_search_messages:294.\r
+>\r
+> I have not been able to make a smaller test case at the moment (this\r
+> happens with offlineimap updating an maildir and notmuch new run\r
+> afterwards + some tagging).\r
+>\r
+> I can work around this by checking for a NULL pointer returned from\r
+> notmuch_query_search_threads () and re-open the database\r
+> (notmuch_database_close () -> notmuch_database_open ()). But I have no\r
+> way of knowing programatically if this really is the error that has\r
+> happened. There should be some way of propagating the error\r
+> information or (even better for my case; for notmuch to reopen the\r
+> database), one option is the Gmime way of passing an pointer to an\r
+> error structure that is filled up by the notmuch interface function.\r
+\r
+Hi again,\r
+\r
+I have not yet been able to create a test for this with a fresh db (I\r
+must be missing out on some of the parts triggering this).\r
+\r
+I need to keep a query open for a while (because running it takes a\r
+while), and this keeps coming back and biting me. I currently do a test\r
+every time I need to access the query further (load more threads..). The\r
+test is as follows, which is the easiest and quickest test I've found to\r
+work reliably:\r
+\r
+\r
+ /* tries to provoke an Xapian::DatabaseModifiedError\r
+ *\r
+ * returns true if db is invalid. queries will be invalid\r
+ * afterwards, but might still respond true to notmuch_valid\r
+ * calls.\r
+ *\r
+ */\r
+\r
+ time_t start =3D clock ();\r
+ bool invalid =3D false;\r
+\r
+ /* testing */\r
+ notmuch_query_t * q =3D notmuch_query_create (nm_db, "thread:fail");\r
+\r
+ /* this will produce an error, but no way to ensure failure */\r
+ notmuch_query_count_threads (q);\r
+\r
+ /* this returns NULL when error */\r
+ notmuch_threads_t * threads =3D notmuch_query_search_threads (q);\r
+\r
+ if (threads =3D=3D NULL) invalid =3D true;\r
+\r
+ notmuch_query_destroy (q);\r
+\r
+ float diff =3D (clock () - start) * 1000.0 / CLOCKS_PER_SEC;\r
+ cout << "db: test query time: " << diff << " ms." << endl;\r
+\r
+ if (invalid) {\r
+ cout << "db: no longer valid, reopen required." << endl;\r
+ } else {\r
+ cout << "db: valid." << endl;\r
+ }\r
+\r
+As mentioned before, I am basically guessing that the reason I get\r
+threads =3D=3D NULL is the DatabaseModifiedError. There is no way to know\r
+for sure.\r
+\r
+For portability I would suggest starting to move towards the GError\r
+scheme provided by glib (also used by gmime). This is a somewhat major\r
+effort though since ensuring that error propagation is done right [0] is\r
+somewhat tricky. It provides more or less the same functionality as\r
+exceptions do in C++.\r
+\r
+There is also the problem of having to change the API - one way to avoid\r
+that is to create wrappers that behave like the old API, but don't\r
+handle errors that good. This requires the addition of addiontal _error\r
+variations of the current set of functions. It will be a mess.\r
+\r
+Cheers, Gaute\r
+\r
+[0] https://developer.gnome.org/glib/stable/glib-Error-Reporting.html\r
+=\r
projects / notmuch-archives.git / commitdiff