From b7c88ab8cc7d55a43450bf3dea750f95f2e910d6 Mon Sep 17 00:00:00 2001 From: Michal Schmidt Date: Tue, 9 Dec 2014 20:27:19 +0100 Subject: [PATCH] journal: optimize iteration: skip whole files behind current location Interleaving of entries from many journal files is expensive. But there is room for optimization. We can skip looking into journal files whose entries all lie before the current iterating location. We can tell if that's the case from looking at the journal file header. This saves a huge amount of work if one has many of mostly not interleaved journal files. On my workstation with 90 journal files in /var/log/journal/ID/ totalling 3.4 GB I get these results: Before: $ time ./journalctl --since=2014-06-01 --until=2014-07-01 > /dev/null real 5m54.258s user 2m4.263s sys 3m48.965s After: $ time ./journalctl --since=2014-06-01 --until=2014-07-01 > /dev/null real 0m20.518s user 0m19.989s sys 0m0.328s The high "sys" time in the original was caused by putting more stress on the mmap-cache than it could handle. With the patch the working set now consists of fewer mmap windows and mmap-cache is not thrashing. --- src/journal/sd-journal.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/src/journal/sd-journal.c b/src/journal/sd-journal.c index bb410ed6e..b937daf5e 100644 --- a/src/journal/sd-journal.c +++ b/src/journal/sd-journal.c @@ -497,6 +497,26 @@ static int compare_entry_order(JournalFile *af, Object *_ao, return 0; } +static bool whole_file_precedes_location(JournalFile *f, Location *l, direction_t direction) { + assert(f); + assert(l); + + if (l->type != LOCATION_DISCRETE && l->type != LOCATION_SEEK) + return false; + + if (l->seqnum_set && sd_id128_equal(l->seqnum_id, f->header->seqnum_id)) + return direction == DIRECTION_DOWN ? + l->seqnum > le64toh(f->header->tail_entry_seqnum) : + l->seqnum < le64toh(f->header->head_entry_seqnum); + + if (l->realtime_set) + return direction == DIRECTION_DOWN ? + l->realtime > le64toh(f->header->tail_entry_realtime) : + l->realtime < le64toh(f->header->head_entry_realtime); + + return false; +} + _pure_ static int compare_with_location(JournalFile *af, Object *ao, Location *l) { uint64_t a; @@ -882,6 +902,9 @@ static int real_journal_next(sd_journal *j, direction_t direction) { ORDERED_HASHMAP_FOREACH(f, j->files, i) { bool found; + if (whole_file_precedes_location(f, &j->current_location, direction)) + continue; + r = next_beyond_location(j, f, direction, &o, &p); if (r < 0) { log_debug_errno(r, "Can't iterate through %s, ignoring: %m", f->path); -- 2.30.2