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Revert "Merge pull request #2394 from wiredtiger/SERVER-21887-sample"

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The change wasn't ready for back port into 3.2.1

This reverts commit 21b5f9951e.
This commit is contained in:
Alex Gorrod 2015-12-22 08:15:10 +00:00
parent 2893117baa
commit b1768d0d9f
1 changed files with 11 additions and 67 deletions
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78
src/btree/row_srch.c
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@ -542,15 +542,12 @@ err: /*
int
__wt_row_random_leaf(WT_SESSION_IMPL *session, WT_CURSOR_BTREE *cbt)
{
WT_INSERT *ins, **start, **stop;
WT_INSERT_HEAD *ins_head;
WT_INSERT *p, *t;
WT_PAGE *page;
uint32_t entries;
int level;
uint32_t cnt;
page = cbt->ref->page;
/* If the page has disk-based entries, select from them. */
if (page->pg_row_entries != 0) {
cbt->compare = 0;
cbt->slot = __wt_random(&session->rnd) % page->pg_row_entries;
@ -565,77 +562,24 @@ __wt_row_random_leaf(WT_SESSION_IMPL *session, WT_CURSOR_BTREE *cbt)
/*
* If the tree is new (and not empty), it might have a large insert
* list.
* list. Count how many records are in the list.
*/
F_SET(cbt, WT_CBT_SEARCH_SMALLEST);
if ((cbt->ins_head = WT_ROW_INSERT_SMALLEST(page)) == NULL)
return (WT_NOTFOUND);
/*
* Walk down the list until we find a level with at least two entries,
* that's where we'll start rolling random numbers.
*/
for (ins_head = cbt->ins_head,
level = WT_SKIP_MAXDEPTH - 1; level > 0; --level)
if ((ins = ins_head->head[level]) != NULL && ins->next != NULL)
for (cnt = 1, p = WT_SKIP_FIRST(cbt->ins_head);; ++cnt)
if ((p = WT_SKIP_NEXT(p)) == NULL)
break;
/*
* Use all entries at this first level as the range for random
* selection. Do that by counting the entries and setting the start
* point as the first entry.
* Select a random number from 0 to (N - 1), return that record.
*/
for (entries = 0,
ins = ins_head->head[level]; ins != NULL; ins = ins->next[level])
++entries;
start = &ins_head->head[level];
/*
* Keep stepping down the skip list selecting a random entry at each
* level. Use all entries as the range the first time through,
* subsequently constrain the range to the entries between the selected
* entry and it's neighbour from a level up the list.
*/
while (level > 0) {
/*
* Select a random number from the calculated entry range and
* convert that to a new start/stop pair. If there are only two
* entries, the start/stop pair must be slots 0 and 1,
* otherwise, use the random number as the start position. The
* calculation uses "entries - 1" to ensure we never chose the
* last node in the list as our new start point.
*/
entries = entries < 3 ?
0 : __wt_random(&session->rnd) % (entries - 1);
/* Move forward to the randomly selected start entry. */
for (; entries > 0; --entries)
start = &(*start)->next[level];
stop = &(*start)->next[level];
/* Drop down a level. */
--start;
--stop;
--level;
/* Count the entries between the new start/stop pair. */
for (entries = 0, ins = *start;
ins != *stop; ++entries, ins = ins->next[level])
;
}
/*
* When we reach the bottom level, select a random entry from the entry
* range and return it.
*
* It should be impossible for the entries count to be 0 at this point,
* but check for it out of paranoia and to quiet static testing tools.
*/
entries = entries < 1 ? 0 : __wt_random(&session->rnd) % entries;
for (ins = *start; entries > 0; --entries)
ins = ins->next[0];
cbt->ins = ins;
cnt = __wt_random(&session->rnd) % cnt;
for (p = t = WT_SKIP_FIRST(cbt->ins_head);; t = p)
if (cnt-- == 0 || (p = WT_SKIP_NEXT(p)) == NULL)
break;
cbt->compare = 0;
cbt->ins = t;
return (0);
}