From 0ad01db952718d3437fa8f077a065d17efe5279b Mon Sep 17 00:00:00 2001

From: Michal Schmidt <mschmidt@redhat.com>

Date: Tue, 24 Feb 2015 19:45:17 +0100

Subject: [PATCH] journal: make skipping of exhausted journal files effective

 again

Commit 668c965af "journal: skipping of exhausted journal files is bad if

direction changed" fixed a correctness issue, but it also significantly

limited the cases where the optimization that skips exhausted journal

files could apply.

As a result, some journalctl queries are much slower in v219 than in v218.

(e.g. queries where a "--since" cutoff should have quickly eliminated

older journal files from consideration, but didn't.)

If already in the initial iteration find_location_with_matches() finds

no entry, the journal file's location is not updated. This is fine,

except that:

 - We must update at least f->last_direction. The optimization relies on

   it. Let's separate that from journal_file_save_location() and update

   it immediately after the direction checks.

 - The optimization was conditional on "f->current_offset > 0", but it

   would always be 0 in this scenario. This check is unnecessary for the

   optimization.

(cherry picked from commit 950c07d421c04e5aae99973479f4f13131fb45e1)

---

 src/journal/journal-file.c |  3 +--

 src/journal/journal-file.h |  2 +-

 src/journal/sd-journal.c   | 24 +++++++++++++++---------

 3 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c

index 0f28718b0e..24c49b916a 100644

--- a/src/journal/journal-file.c

+++ b/src/journal/journal-file.c

@@ -2014,8 +2014,7 @@ void journal_file_reset_location(JournalFile *f) {

         f->current_xor_hash = 0;

 }

-void journal_file_save_location(JournalFile *f, direction_t direction, Object *o, uint64_t offset) {

-        f->last_direction = direction;

+void journal_file_save_location(JournalFile *f, Object *o, uint64_t offset) {

         f->location_type = LOCATION_SEEK;

         f->current_offset = offset;

         f->current_seqnum = le64toh(o->entry.seqnum);

diff --git a/src/journal/journal-file.h b/src/journal/journal-file.h

index 2526e14d65..403c8f760c 100644

--- a/src/journal/journal-file.h

+++ b/src/journal/journal-file.h

@@ -199,7 +199,7 @@ int journal_file_find_field_object(JournalFile *f, const void *field, uint64_t s

 int journal_file_find_field_object_with_hash(JournalFile *f, const void *field, uint64_t size, uint64_t hash, Object **ret, uint64_t *offset);

 void journal_file_reset_location(JournalFile *f);

-void journal_file_save_location(JournalFile *f, direction_t direction, Object *o, uint64_t offset);

+void journal_file_save_location(JournalFile *f, Object *o, uint64_t offset);

 int journal_file_compare_locations(JournalFile *af, JournalFile *bf);

 int journal_file_next_entry(JournalFile *f, uint64_t p, direction_t direction, Object **ret, uint64_t *offset);

diff --git a/src/journal/sd-journal.c b/src/journal/sd-journal.c

index 94891cdf35..9b57e5945d 100644

--- a/src/journal/sd-journal.c

+++ b/src/journal/sd-journal.c

@@ -723,13 +723,17 @@ static int next_beyond_location(sd_journal *j, JournalFile *f, direction_t direc

         assert(j);

         assert(f);

-        if (f->last_direction == direction && f->current_offset > 0) {

-                /* If we hit EOF before, recheck if any new entries arrived. */

-                n_entries = le64toh(f->header->n_entries);

-                if (f->location_type == LOCATION_TAIL && n_entries == f->last_n_entries)

-                        return 0;

-                f->last_n_entries = n_entries;

+        n_entries = le64toh(f->header->n_entries);

+

+        /* If we hit EOF before, we don't need to look into this file again

+         * unless direction changed or new entries appeared. */

+        if (f->last_direction == direction && f->location_type == LOCATION_TAIL &&

+            n_entries == f->last_n_entries)

+                return 0;

+        f->last_n_entries = n_entries;

+

+        if (f->last_direction == direction && f->current_offset > 0) {

                 /* LOCATION_SEEK here means we did the work in a previous

                  * iteration and the current location already points to a

                  * candidate entry. */

@@ -738,14 +742,16 @@ static int next_beyond_location(sd_journal *j, JournalFile *f, direction_t direc

                         if (r <= 0)

                                 return r;

-                        journal_file_save_location(f, direction, c, cp);

+                        journal_file_save_location(f, c, cp);

                 }

         } else {

+                f->last_direction = direction;

+

                 r = find_location_with_matches(j, f, direction, &c, &cp;;

                 if (r <= 0)

                         return r;

-                journal_file_save_location(f, direction, c, cp);

+                journal_file_save_location(f, c, cp);

         }

         /* OK, we found the spot, now let's advance until an entry

@@ -773,7 +779,7 @@ static int next_beyond_location(sd_journal *j, JournalFile *f, direction_t direc

                 if (r <= 0)

                         return r;

-                journal_file_save_location(f, direction, c, cp);

+                journal_file_save_location(f, c, cp);

         }

 }