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From 563bf9e9305aa88ad403a81c0c91418b7846f465 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Tue, 26 Nov 2013 20:37:53 +0100
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Subject: [PATCH] journal: optimize bisection logic a bit by caching the last
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position
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This way we can do a quick restart limiting a bit how wildly we need to
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jump around during the bisection process.
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---
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src/journal/journal-file.c | 134 +++++++++++++++++++++++++++++++++------------
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1 file changed, 99 insertions(+), 35 deletions(-)
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diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
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index 4062a83..7adb1b5 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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@@ -1366,6 +1366,7 @@ typedef struct ChainCacheItem {
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uint64_t array; /* the cached array */
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uint64_t begin; /* the first item in the cached array */
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uint64_t total; /* the total number of items in all arrays before this one in the chain */
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+ uint64_t last_index; /* the last index we looked at, to optimize locality when bisecting */
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} ChainCacheItem;
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static void chain_cache_put(
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@@ -1374,7 +1375,8 @@ static void chain_cache_put(
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uint64_t first,
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uint64_t array,
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uint64_t begin,
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- uint64_t total) {
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+ uint64_t total,
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+ uint64_t last_index) {
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if (!ci) {
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/* If the chain item to cache for this chain is the
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@@ -1402,12 +1404,14 @@ static void chain_cache_put(
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ci->array = array;
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ci->begin = begin;
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ci->total = total;
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+ ci->last_index = last_index;
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}
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-static int generic_array_get(JournalFile *f,
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- uint64_t first,
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- uint64_t i,
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- Object **ret, uint64_t *offset) {
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+static int generic_array_get(
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+ JournalFile *f,
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+ uint64_t first,
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+ uint64_t i,
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+ Object **ret, uint64_t *offset) {
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Object *o;
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uint64_t p = 0, a, t = 0;
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@@ -1448,7 +1452,7 @@ static int generic_array_get(JournalFile *f,
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found:
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/* Let's cache this item for the next invocation */
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- chain_cache_put(f->chain_cache, ci, first, a, o->entry_array.items[0], t);
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+ chain_cache_put(f->chain_cache, ci, first, a, o->entry_array.items[0], t, i);
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r = journal_file_move_to_object(f, OBJECT_ENTRY, p, &o);
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if (r < 0)
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@@ -1463,11 +1467,12 @@ found:
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return 1;
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}
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-static int generic_array_get_plus_one(JournalFile *f,
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- uint64_t extra,
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- uint64_t first,
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- uint64_t i,
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- Object **ret, uint64_t *offset) {
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+static int generic_array_get_plus_one(
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+ JournalFile *f,
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+ uint64_t extra,
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+ uint64_t first,
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+ uint64_t i,
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+ Object **ret, uint64_t *offset) {
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Object *o;
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@@ -1498,17 +1503,18 @@ enum {
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TEST_RIGHT
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};
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-static int generic_array_bisect(JournalFile *f,
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- uint64_t first,
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- uint64_t n,
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- uint64_t needle,
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- int (*test_object)(JournalFile *f, uint64_t p, uint64_t needle),
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- direction_t direction,
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- Object **ret,
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- uint64_t *offset,
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- uint64_t *idx) {
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-
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- uint64_t a, p, t = 0, i = 0, last_p = 0;
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+static int generic_array_bisect(
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+ JournalFile *f,
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+ uint64_t first,
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+ uint64_t n,
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+ uint64_t needle,
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+ int (*test_object)(JournalFile *f, uint64_t p, uint64_t needle),
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+ direction_t direction,
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+ Object **ret,
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+ uint64_t *offset,
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+ uint64_t *idx) {
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+
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+ uint64_t a, p, t = 0, i = 0, last_p = 0, last_index = (uint64_t) -1;
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bool subtract_one = false;
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Object *o, *array = NULL;
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int r;
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@@ -1533,7 +1539,7 @@ static int generic_array_bisect(JournalFile *f,
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return r;
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if (r == TEST_LEFT) {
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- /* OK, what we are looking for is right of th
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+ /* OK, what we are looking for is right of the
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* begin of this EntryArray, so let's jump
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* straight to previously cached array in the
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* chain */
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@@ -1541,6 +1547,7 @@ static int generic_array_bisect(JournalFile *f,
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a = ci->array;
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n -= ci->total;
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t = ci->total;
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+ last_index = ci->last_index;
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}
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}
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@@ -1571,6 +1578,60 @@ static int generic_array_bisect(JournalFile *f,
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if (r == TEST_RIGHT) {
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left = 0;
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right -= 1;
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+
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+ if (last_index != (uint64_t) -1) {
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+ assert(last_index <= right);
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+
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+ /* If we cached the last index we
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+ * looked at, let's try to not to jump
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+ * too wildly around and see if we can
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+ * limit the range to look at early to
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+ * the immediate neighbors of the last
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+ * index we looked at. */
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+
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+ if (last_index > 0) {
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+ uint64_t x = last_index - 1;
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+
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+ p = le64toh(array->entry_array.items[x]);
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+ if (p <= 0)
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+ return -EBADMSG;
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+
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+ r = test_object(f, p, needle);
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+ if (r < 0)
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+ return r;
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+
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+ if (r == TEST_FOUND)
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+ r = direction == DIRECTION_DOWN ? TEST_RIGHT : TEST_LEFT;
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+
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+ if (r == TEST_RIGHT)
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+ right = x;
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+ else
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+ left = x + 1;
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+ }
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+
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+ if (last_index < right) {
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+ uint64_t y = last_index + 1;
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+
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+ p = le64toh(array->entry_array.items[y]);
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+ if (p <= 0)
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+ return -EBADMSG;
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+
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+ r = test_object(f, p, needle);
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+ if (r < 0)
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+ return r;
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+
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+ if (r == TEST_FOUND)
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+ r = direction == DIRECTION_DOWN ? TEST_RIGHT : TEST_LEFT;
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+
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+ if (r == TEST_RIGHT)
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+ right = y;
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+ else
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+ left = y + 1;
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+ }
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+
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+ last_index = (uint64_t) -1;
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+ }
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+
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for (;;) {
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if (left == right) {
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if (direction == DIRECTION_UP)
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@@ -1581,8 +1642,8 @@ static int generic_array_bisect(JournalFile *f,
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}
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assert(left < right);
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-
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i = (left + right) / 2;
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+
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p = le64toh(array->entry_array.items[i]);
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if (p <= 0)
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return -EBADMSG;
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@@ -1615,6 +1676,7 @@ static int generic_array_bisect(JournalFile *f,
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n -= k;
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t += k;
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+ last_index = (uint64_t) -1;
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a = le64toh(array->entry_array.next_entry_array_offset);
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}
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@@ -1625,7 +1687,7 @@ found:
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return 0;
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/* Let's cache this item for the next invocation */
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- chain_cache_put(f->chain_cache, ci, first, a, array->entry_array.items[0], t);
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+ chain_cache_put(f->chain_cache, ci, first, a, array->entry_array.items[0], t, i + (subtract_one ? -1 : 0));
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if (subtract_one && i == 0)
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p = last_p;
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@@ -1650,16 +1712,18 @@ found:
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return 1;
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}
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-static int generic_array_bisect_plus_one(JournalFile *f,
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- uint64_t extra,
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- uint64_t first,
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- uint64_t n,
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- uint64_t needle,
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- int (*test_object)(JournalFile *f, uint64_t p, uint64_t needle),
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- direction_t direction,
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- Object **ret,
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- uint64_t *offset,
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- uint64_t *idx) {
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+
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+static int generic_array_bisect_plus_one(
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+ JournalFile *f,
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+ uint64_t extra,
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+ uint64_t first,
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+ uint64_t n,
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+ uint64_t needle,
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+ int (*test_object)(JournalFile *f, uint64_t p, uint64_t needle),
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+ direction_t direction,
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+ Object **ret,
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+ uint64_t *offset,
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+ uint64_t *idx) {
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int r;
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bool step_back = false;
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