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journal: optimize iteration: skip files that cannot improve current candidate entry
Suppose that while iterating we have already looked into a journal file and got a candidate for the next entry. And we are considering to look into another journal file because it may contain an entry that is nearer to the current location than the candidate. We should skip the whole journal file if we can tell by looking at its header that none of its entries can precede the candidate. Before: $ time ./journalctl --since=2014-06-01 --until=2014-07-01 > /dev/null real 0m20.518s user 0m19.989s sys 0m0.328s After: $ time ./journalctl --since=2014-06-01 --until=2014-07-01 > /dev/null real 0m9.445s user 0m9.228s sys 0m0.213s
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@ -517,6 +517,27 @@ static bool whole_file_precedes_location(JournalFile *f, Location *l, direction_
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return false;
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}
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static bool file_may_have_preceding_entry(JournalFile *f, JournalFile *of, uint64_t op, direction_t direction) {
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Object *o;
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int r;
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assert(f);
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assert(of);
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r = journal_file_move_to_object(of, OBJECT_ENTRY, op, &o);
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if (r < 0)
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return true;
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if (sd_id128_equal(f->header->seqnum_id, of->header->seqnum_id))
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return direction == DIRECTION_DOWN ?
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le64toh(o->entry.seqnum) >= le64toh(f->header->head_entry_seqnum) :
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le64toh(o->entry.seqnum) <= le64toh(f->header->tail_entry_seqnum);
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return direction == DIRECTION_DOWN ?
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le64toh(o->entry.realtime) >= le64toh(f->header->head_entry_realtime) :
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le64toh(o->entry.realtime) <= le64toh(f->header->tail_entry_realtime);
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}
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_pure_ static int compare_with_location(JournalFile *af, Object *ao, Location *l) {
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uint64_t a;
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@ -905,6 +926,9 @@ static int real_journal_next(sd_journal *j, direction_t direction) {
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if (whole_file_precedes_location(f, &j->current_location, direction))
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continue;
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if (new_file && !file_may_have_preceding_entry(f, new_file, new_offset, direction))
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continue;
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r = next_beyond_location(j, f, direction, &o, &p);
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if (r < 0) {
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log_debug_errno(r, "Can't iterate through %s, ignoring: %m", f->path);
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