From a460644e808ed7671e28ef8231ee590317371fed Mon Sep 17 00:00:00 2001

From: Lennart Poettering <lennart@poettering.net>

Date: Tue, 26 Nov 2013 20:37:53 +0100

Subject: [PATCH] journal: optimize bisection logic a bit by caching the last

 position

This way we can do a quick restart limiting a bit how wildly we need to

jump around during the bisection process.

(cherry picked from commit f268980d2cee694fa4118a71402a47c316af0425)

---

 src/journal/journal-file.c | 134 +++++++++++++++++++++++++++++++++------------

 1 file changed, 99 insertions(+), 35 deletions(-)

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

index d3bdaea..02f7554 100644

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

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

@@ -1366,6 +1366,7 @@ typedef struct ChainCacheItem {

         uint64_t array; /* the cached array */

         uint64_t begin; /* the first item in the cached array */

         uint64_t total; /* the total number of items in all arrays before this one in the chain */

+        uint64_t last_index; /* the last index we looked at, to optimize locality when bisecting */

 } ChainCacheItem;

 static void chain_cache_put(

@@ -1374,7 +1375,8 @@ static void chain_cache_put(

                 uint64_t first,

                 uint64_t array,

                 uint64_t begin,

-                uint64_t total) {

+                uint64_t total,

+                uint64_t last_index) {

         if (!ci) {

                 /* If the chain item to cache for this chain is the

@@ -1402,12 +1404,14 @@ static void chain_cache_put(

         ci->array = array;

         ci->begin = begin;

         ci->total = total;

+        ci->last_index = last_index;

 }

-static int generic_array_get(JournalFile *f,

-                             uint64_t first,

-                             uint64_t i,

-                             Object **ret, uint64_t *offset) {

+static int generic_array_get(

+                JournalFile *f,

+                uint64_t first,

+                uint64_t i,

+                Object **ret, uint64_t *offset) {

         Object *o;

         uint64_t p = 0, a, t = 0;

@@ -1448,7 +1452,7 @@ static int generic_array_get(JournalFile *f,

 found:

         /* Let's cache this item for the next invocation */

-        chain_cache_put(f->chain_cache, ci, first, a, o->entry_array.items[0], t);

+        chain_cache_put(f->chain_cache, ci, first, a, o->entry_array.items[0], t, i);

         r = journal_file_move_to_object(f, OBJECT_ENTRY, p, &o);

         if (r < 0)

@@ -1463,11 +1467,12 @@ found:

         return 1;

 }

-static int generic_array_get_plus_one(JournalFile *f,

-                                      uint64_t extra,

-                                      uint64_t first,

-                                      uint64_t i,

-                                      Object **ret, uint64_t *offset) {

+static int generic_array_get_plus_one(

+                JournalFile *f,

+                uint64_t extra,

+                uint64_t first,

+                uint64_t i,

+                Object **ret, uint64_t *offset) {

         Object *o;

@@ -1498,17 +1503,18 @@ enum {

         TEST_RIGHT

 };

-static int generic_array_bisect(JournalFile *f,

-                                uint64_t first,

-                                uint64_t n,

-                                uint64_t needle,

-                                int (*test_object)(JournalFile *f, uint64_t p, uint64_t needle),

-                                direction_t direction,

-                                Object **ret,

-                                uint64_t *offset,

-                                uint64_t *idx) {

-

-        uint64_t a, p, t = 0, i = 0, last_p = 0;

+static int generic_array_bisect(

+                JournalFile *f,

+                uint64_t first,

+                uint64_t n,

+                uint64_t needle,

+                int (*test_object)(JournalFile *f, uint64_t p, uint64_t needle),

+                direction_t direction,

+                Object **ret,

+                uint64_t *offset,

+                uint64_t *idx) {

+

+        uint64_t a, p, t = 0, i = 0, last_p = 0, last_index = (uint64_t) -1;

         bool subtract_one = false;

         Object *o, *array = NULL;

         int r;

@@ -1533,7 +1539,7 @@ static int generic_array_bisect(JournalFile *f,

                         return r;

                 if (r == TEST_LEFT) {

-                        /* OK, what we are looking for is right of th

+                        /* OK, what we are looking for is right of the

                          * begin of this EntryArray, so let's jump

                          * straight to previously cached array in the

                          * chain */

@@ -1541,6 +1547,7 @@ static int generic_array_bisect(JournalFile *f,

                         a = ci->array;

                         n -= ci->total;

                         t = ci->total;

+                        last_index = ci->last_index;

                 }

         }

@@ -1571,6 +1578,60 @@ static int generic_array_bisect(JournalFile *f,

                 if (r == TEST_RIGHT) {

                         left = 0;

                         right -= 1;

+

+                        if (last_index != (uint64_t) -1) {

+                                assert(last_index <= right);

+

+                                /* If we cached the last index we

+                                 * looked at, let's try to not to jump

+                                 * too wildly around and see if we can

+                                 * limit the range to look at early to

+                                 * the immediate neighbors of the last

+                                 * index we looked at. */

+

+                                if (last_index > 0) {

+                                        uint64_t x = last_index - 1;

+

+                                        p = le64toh(array->entry_array.items[x]);

+                                        if (p <= 0)

+                                                return -EBADMSG;

+

+                                        r = test_object(f, p, needle);

+                                        if (r < 0)

+                                                return r;

+

+                                        if (r == TEST_FOUND)

+                                                r = direction == DIRECTION_DOWN ? TEST_RIGHT : TEST_LEFT;

+

+                                        if (r == TEST_RIGHT)

+                                                right = x;

+                                        else

+                                                left = x + 1;

+                                }

+

+                                if (last_index < right) {

+                                        uint64_t y = last_index + 1;

+

+                                        p = le64toh(array->entry_array.items[y]);

+                                        if (p <= 0)

+                                                return -EBADMSG;

+

+                                        r = test_object(f, p, needle);

+                                        if (r < 0)

+                                                return r;

+

+                                        if (r == TEST_FOUND)

+                                                r = direction == DIRECTION_DOWN ? TEST_RIGHT : TEST_LEFT;

+

+                                        if (r == TEST_RIGHT)

+                                                right = y;

+                                        else

+                                                left = y + 1;

+                                }

+

+                                last_index = (uint64_t) -1;

+                        }

+

                         for (;;) {

                                 if (left == right) {

                                         if (direction == DIRECTION_UP)

@@ -1581,8 +1642,8 @@ static int generic_array_bisect(JournalFile *f,

                                 }

                                 assert(left < right);

-

                                 i = (left + right) / 2;

+

                                 p = le64toh(array->entry_array.items[i]);

                                 if (p <= 0)

                                         return -EBADMSG;

@@ -1615,6 +1676,7 @@ static int generic_array_bisect(JournalFile *f,

                 n -= k;

                 t += k;

+                last_index = (uint64_t) -1;

                 a = le64toh(array->entry_array.next_entry_array_offset);

         }

@@ -1625,7 +1687,7 @@ found:

                 return 0;

         /* Let's cache this item for the next invocation */

-        chain_cache_put(f->chain_cache, ci, first, a, array->entry_array.items[0], t);

+        chain_cache_put(f->chain_cache, ci, first, a, array->entry_array.items[0], t, i + (subtract_one ? -1 : 0));

         if (subtract_one && i == 0)

                 p = last_p;

@@ -1650,16 +1712,18 @@ found:

         return 1;

 }

-static int generic_array_bisect_plus_one(JournalFile *f,

-                                         uint64_t extra,

-                                         uint64_t first,

-                                         uint64_t n,

-                                         uint64_t needle,

-                                         int (*test_object)(JournalFile *f, uint64_t p, uint64_t needle),

-                                         direction_t direction,

-                                         Object **ret,

-                                         uint64_t *offset,

-                                         uint64_t *idx) {

+

+static int generic_array_bisect_plus_one(

+                JournalFile *f,

+                uint64_t extra,

+                uint64_t first,

+                uint64_t n,

+                uint64_t needle,

+                int (*test_object)(JournalFile *f, uint64_t p, uint64_t needle),

+                direction_t direction,

+                Object **ret,

+                uint64_t *offset,

+                uint64_t *idx) {

         int r;

         bool step_back = false;