From 7f57b747b95eece465d10fd0acba20cc3dd868f1 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Mon, 13 Oct 2014 02:20:01 -0400 Subject: [PATCH] lib: Add per-message last modification tracking This adds a new document value that stores the revision of the last modification to message metadata, where the revision number increases monotonically with each database commit. An alternative would be to store the wall-clock time of the last modification of each message. In principle this is simpler and has the advantage that any process can determine the current timestamp without support from libnotmuch. However, even assuming a computer's clock never goes backward and ignoring clock skew in networked environments, this has a fatal flaw. Xapian uses (optimistic) snapshot isolation, which means reads can be concurrent with writes. Given this, consider the following time line with a write and two read transactions: write |-X-A--------------| read 1 |---B---| read 2 |---| The write transaction modifies message X and records the wall-clock time of the modification at A. The writer hangs around for a while and later commits its change. Read 1 is concurrent with the write, so it doesn't see the change to X. It does some query and records the wall-clock time of its results at B. Transaction read 2 later starts after the write commits and queries for changes since wall-clock time B (say the reads are performing an incremental backup). Even though read 1 could not see the change to X, read 2 is told (correctly) that X has not changed since B, the time of the last read. In fact, X changed before wall-clock time A, but the change was not visible until *after* wall-clock time B, so read 2 misses the change to X. This is tricky to solve in full-blown snapshot isolation, but because Xapian serializes writes, we can use a simple, monotonically increasing database revision number. Furthermore, maintaining this revision number requires no more IO than a wall-clock time solution because Xapian already maintains statistics on the upper (and lower) bound of each value stream. --- lib/database-private.h | 16 +++++++++++++- lib/database.cc | 50 ++++++++++++++++++++++++++++++++++++++++-- lib/message.cc | 22 +++++++++++++++++++ lib/notmuch-private.h | 10 ++++++++- 4 files changed, 94 insertions(+), 4 deletions(-) diff --git a/lib/database-private.h b/lib/database-private.h index 24243db2..5c5a2bb2 100644 --- a/lib/database-private.h +++ b/lib/database-private.h @@ -100,6 +100,12 @@ enum _notmuch_features { * * Introduced: version 3. */ NOTMUCH_FEATURE_INDEXED_MIMETYPES = 1 << 5, + + /* If set, messages store the revision number of the last + * modification in NOTMUCH_VALUE_LAST_MOD. + * + * Introduced: version 3. */ + NOTMUCH_FEATURE_LAST_MOD = 1 << 6, }; /* In C++, a named enum is its own type, so define bitwise operators @@ -145,6 +151,8 @@ struct _notmuch_database { notmuch_database_mode_t mode; int atomic_nesting; + /* TRUE if changes have been made in this atomic section */ + notmuch_bool_t atomic_dirty; Xapian::Database *xapian_db; /* Bit mask of features used by this database. This is a @@ -158,6 +166,11 @@ struct _notmuch_database { * next library call. May be NULL */ char *status_string; + /* Highest committed revision number. Modifications are recorded + * under a higher revision number, which can be generated with + * notmuch_database_new_revision. */ + unsigned long revision; + Xapian::QueryParser *query_parser; Xapian::TermGenerator *term_gen; Xapian::ValueRangeProcessor *value_range_processor; @@ -179,7 +192,8 @@ struct _notmuch_database { * will have it). */ #define NOTMUCH_FEATURES_CURRENT \ (NOTMUCH_FEATURE_FILE_TERMS | NOTMUCH_FEATURE_DIRECTORY_DOCS | \ - NOTMUCH_FEATURE_BOOL_FOLDER | NOTMUCH_FEATURE_GHOSTS) + NOTMUCH_FEATURE_BOOL_FOLDER | NOTMUCH_FEATURE_GHOSTS | \ + NOTMUCH_FEATURE_LAST_MOD) /* Return the list of terms from the given iterator matching a prefix. * The prefix will be stripped from the strings in the returned list. diff --git a/lib/database.cc b/lib/database.cc index 6a151749..52e2e8f1 100644 --- a/lib/database.cc +++ b/lib/database.cc @@ -101,6 +101,9 @@ typedef struct { * * SUBJECT: The value of the "Subject" header * + * LAST_MOD: The revision number as of the last tag or + * filename change. + * * In addition, terms from the content of the message are added with * "from", "to", "attachment", and "subject" prefixes for use by the * user in searching. Similarly, terms from the path of the mail @@ -310,6 +313,8 @@ static const struct { * them. */ { NOTMUCH_FEATURE_INDEXED_MIMETYPES, "indexed MIME types", "w"}, + { NOTMUCH_FEATURE_LAST_MOD, + "modification tracking", "w"}, }; const char * @@ -737,6 +742,23 @@ _notmuch_database_ensure_writable (notmuch_database_t *notmuch) return NOTMUCH_STATUS_SUCCESS; } +/* Allocate a revision number for the next change. */ +unsigned long +_notmuch_database_new_revision (notmuch_database_t *notmuch) +{ + unsigned long new_revision = notmuch->revision + 1; + + /* If we're in an atomic section, hold off on updating the + * committed revision number until we commit the atomic section. + */ + if (notmuch->atomic_nesting) + notmuch->atomic_dirty = TRUE; + else + notmuch->revision = new_revision; + + return new_revision; +} + /* Parse a database features string from the given database version. * Returns the feature bit set. * @@ -904,6 +926,7 @@ notmuch_database_open_verbose (const char *path, notmuch->atomic_nesting = 0; try { string last_thread_id; + string last_mod; if (mode == NOTMUCH_DATABASE_MODE_READ_WRITE) { notmuch->xapian_db = new Xapian::WritableDatabase (xapian_path, @@ -962,6 +985,14 @@ notmuch_database_open_verbose (const char *path, INTERNAL_ERROR ("Malformed database last_thread_id: %s", str); } + /* Get current highest revision number. */ + last_mod = notmuch->xapian_db->get_value_upper_bound ( + NOTMUCH_VALUE_LAST_MOD); + if (last_mod.empty ()) + notmuch->revision = 0; + else + notmuch->revision = Xapian::sortable_unserialise (last_mod); + notmuch->query_parser = new Xapian::QueryParser; notmuch->term_gen = new Xapian::TermGenerator; notmuch->term_gen->set_stemmer (Xapian::Stem ("english")); @@ -1369,7 +1400,8 @@ notmuch_database_upgrade (notmuch_database_t *notmuch, /* Figure out how much total work we need to do. */ if (new_features & - (NOTMUCH_FEATURE_FILE_TERMS | NOTMUCH_FEATURE_BOOL_FOLDER)) { + (NOTMUCH_FEATURE_FILE_TERMS | NOTMUCH_FEATURE_BOOL_FOLDER | + NOTMUCH_FEATURE_LAST_MOD)) { notmuch_query_t *query = notmuch_query_create (notmuch, ""); total += notmuch_query_count_messages (query); notmuch_query_destroy (query); @@ -1396,7 +1428,8 @@ notmuch_database_upgrade (notmuch_database_t *notmuch, /* Perform per-message upgrades. */ if (new_features & - (NOTMUCH_FEATURE_FILE_TERMS | NOTMUCH_FEATURE_BOOL_FOLDER)) { + (NOTMUCH_FEATURE_FILE_TERMS | NOTMUCH_FEATURE_BOOL_FOLDER | + NOTMUCH_FEATURE_LAST_MOD)) { notmuch_query_t *query = notmuch_query_create (notmuch, ""); notmuch_messages_t *messages; notmuch_message_t *message; @@ -1433,6 +1466,14 @@ notmuch_database_upgrade (notmuch_database_t *notmuch, if (new_features & NOTMUCH_FEATURE_BOOL_FOLDER) _notmuch_message_upgrade_folder (message); + /* Prior to NOTMUCH_FEATURE_LAST_MOD, messages did not + * track modification revisions. Give all messages the + * next available revision; since we just started tracking + * revisions for this database, that will be 1. + */ + if (new_features & NOTMUCH_FEATURE_LAST_MOD) + _notmuch_message_upgrade_last_mod (message); + _notmuch_message_sync (message); notmuch_message_destroy (message); @@ -1615,6 +1656,11 @@ notmuch_database_end_atomic (notmuch_database_t *notmuch) return NOTMUCH_STATUS_XAPIAN_EXCEPTION; } + if (notmuch->atomic_dirty) { + ++notmuch->revision; + notmuch->atomic_dirty = FALSE; + } + DONE: notmuch->atomic_nesting--; return NOTMUCH_STATUS_SUCCESS; diff --git a/lib/message.cc b/lib/message.cc index 1ddce3c6..26b5e76e 100644 --- a/lib/message.cc +++ b/lib/message.cc @@ -998,6 +998,16 @@ _notmuch_message_set_header_values (notmuch_message_t *message, message->modified = TRUE; } +/* Upgrade a message to support NOTMUCH_FEATURE_LAST_MOD. The caller + * must call _notmuch_message_sync. */ +void +_notmuch_message_upgrade_last_mod (notmuch_message_t *message) +{ + /* _notmuch_message_sync will update the last modification + * revision; we just have to ask it to. */ + message->modified = TRUE; +} + /* Synchronize changes made to message->doc out into the database. */ void _notmuch_message_sync (notmuch_message_t *message) @@ -1010,6 +1020,18 @@ _notmuch_message_sync (notmuch_message_t *message) if (! message->modified) return; + /* Update the last modification of this message. */ + if (message->notmuch->features & NOTMUCH_FEATURE_LAST_MOD) + /* sortable_serialise gives a reasonably compact encoding, + * which directly translates to reduced IO when scanning the + * value stream. Since it's built for doubles, we only get 53 + * effective bits, but that's still enough for the database to + * last a few centuries at 1 million revisions per second. */ + message->doc.add_value (NOTMUCH_VALUE_LAST_MOD, + Xapian::sortable_serialise ( + _notmuch_database_new_revision ( + message->notmuch))); + db = static_cast (message->notmuch->xapian_db); db->replace_document (message->doc_id, message->doc); message->modified = FALSE; diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h index cc9ce12c..f52b4e47 100644 --- a/lib/notmuch-private.h +++ b/lib/notmuch-private.h @@ -107,7 +107,8 @@ typedef enum { NOTMUCH_VALUE_TIMESTAMP = 0, NOTMUCH_VALUE_MESSAGE_ID, NOTMUCH_VALUE_FROM, - NOTMUCH_VALUE_SUBJECT + NOTMUCH_VALUE_SUBJECT, + NOTMUCH_VALUE_LAST_MOD, } notmuch_value_t; /* Xapian (with flint backend) complains if we provide a term longer @@ -194,6 +195,9 @@ void _notmuch_database_log (notmuch_database_t *notmuch, const char *format, ...); +unsigned long +_notmuch_database_new_revision (notmuch_database_t *notmuch); + const char * _notmuch_database_relative_path (notmuch_database_t *notmuch, const char *path); @@ -305,6 +309,10 @@ _notmuch_message_set_header_values (notmuch_message_t *message, const char *date, const char *from, const char *subject); + +void +_notmuch_message_upgrade_last_mod (notmuch_message_t *message); + void _notmuch_message_sync (notmuch_message_t *message); -- 2.26.2