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From 0ad01db952718d3437fa8f077a065d17efe5279b Mon Sep 17 00:00:00 2001
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From: Michal Schmidt <mschmidt@redhat.com>
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Date: Tue, 24 Feb 2015 19:45:17 +0100
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Subject: [PATCH] journal: make skipping of exhausted journal files effective
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 again
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Commit 668c965af "journal: skipping of exhausted journal files is bad if
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direction changed" fixed a correctness issue, but it also significantly
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limited the cases where the optimization that skips exhausted journal
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files could apply.
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As a result, some journalctl queries are much slower in v219 than in v218.
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(e.g. queries where a "--since" cutoff should have quickly eliminated
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older journal files from consideration, but didn't.)
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If already in the initial iteration find_location_with_matches() finds
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no entry, the journal file's location is not updated. This is fine,
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except that:
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 - We must update at least f->last_direction. The optimization relies on
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   it. Let's separate that from journal_file_save_location() and update
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   it immediately after the direction checks.
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 - The optimization was conditional on "f->current_offset > 0", but it
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   would always be 0 in this scenario. This check is unnecessary for the
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   optimization.
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(cherry picked from commit 950c07d421c04e5aae99973479f4f13131fb45e1)
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---
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 src/journal/journal-file.c |  3 +--
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 src/journal/journal-file.h |  2 +-
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 src/journal/sd-journal.c   | 24 +++++++++++++++---------
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 3 files changed, 17 insertions(+), 12 deletions(-)
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diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
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index 0f28718b0..24c49b916 100644
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--- a/src/journal/journal-file.c
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+++ b/src/journal/journal-file.c
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@@ -2014,8 +2014,7 @@ void journal_file_reset_location(JournalFile *f) {
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         f->current_xor_hash = 0;
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 }
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-void journal_file_save_location(JournalFile *f, direction_t direction, Object *o, uint64_t offset) {
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-        f->last_direction = direction;
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+void journal_file_save_location(JournalFile *f, Object *o, uint64_t offset) {
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         f->location_type = LOCATION_SEEK;
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         f->current_offset = offset;
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         f->current_seqnum = le64toh(o->entry.seqnum);
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diff --git a/src/journal/journal-file.h b/src/journal/journal-file.h
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index 2526e14d6..403c8f760 100644
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--- a/src/journal/journal-file.h
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+++ b/src/journal/journal-file.h
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@@ -199,7 +199,7 @@ int journal_file_find_field_object(JournalFile *f, const void *field, uint64_t s
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 int journal_file_find_field_object_with_hash(JournalFile *f, const void *field, uint64_t size, uint64_t hash, Object **ret, uint64_t *offset);
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 void journal_file_reset_location(JournalFile *f);
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-void journal_file_save_location(JournalFile *f, direction_t direction, Object *o, uint64_t offset);
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+void journal_file_save_location(JournalFile *f, Object *o, uint64_t offset);
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 int journal_file_compare_locations(JournalFile *af, JournalFile *bf);
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 int journal_file_next_entry(JournalFile *f, uint64_t p, direction_t direction, Object **ret, uint64_t *offset);
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diff --git a/src/journal/sd-journal.c b/src/journal/sd-journal.c
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index 94891cdf3..9b57e5945 100644
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--- a/src/journal/sd-journal.c
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+++ b/src/journal/sd-journal.c
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@@ -723,13 +723,17 @@ static int next_beyond_location(sd_journal *j, JournalFile *f, direction_t direc
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         assert(j);
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         assert(f);
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-        if (f->last_direction == direction && f->current_offset > 0) {
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-                /* If we hit EOF before, recheck if any new entries arrived. */
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-                n_entries = le64toh(f->header->n_entries);
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-                if (f->location_type == LOCATION_TAIL && n_entries == f->last_n_entries)
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-                        return 0;
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-                f->last_n_entries = n_entries;
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+        n_entries = le64toh(f->header->n_entries);
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+
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+        /* If we hit EOF before, we don't need to look into this file again
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+         * unless direction changed or new entries appeared. */
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+        if (f->last_direction == direction && f->location_type == LOCATION_TAIL &&
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+            n_entries == f->last_n_entries)
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+                return 0;
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+        f->last_n_entries = n_entries;
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+
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+        if (f->last_direction == direction && f->current_offset > 0) {
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                 /* LOCATION_SEEK here means we did the work in a previous
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                  * iteration and the current location already points to a
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                  * candidate entry. */
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@@ -738,14 +742,16 @@ static int next_beyond_location(sd_journal *j, JournalFile *f, direction_t direc
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                         if (r <= 0)
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                                 return r;
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-                        journal_file_save_location(f, direction, c, cp);
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+                        journal_file_save_location(f, c, cp);
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                 }
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         } else {
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+                f->last_direction = direction;
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+
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                 r = find_location_with_matches(j, f, direction, &c, &cp;;
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                 if (r <= 0)
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                         return r;
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-                journal_file_save_location(f, direction, c, cp);
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+                journal_file_save_location(f, c, cp);
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         }
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         /* OK, we found the spot, now let's advance until an entry
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@@ -773,7 +779,7 @@ static int next_beyond_location(sd_journal *j, JournalFile *f, direction_t direc
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                 if (r <= 0)
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                         return r;
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-                journal_file_save_location(f, direction, c, cp);
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+                journal_file_save_location(f, c, cp);
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         }
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 }
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