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Simplify list traversal logic in add_path().

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Its mechanism for recovering after deleting the current list cell was
a bit klugy.  Borrow the technique used in other places.
This commit is contained in:
Tom Lane 2011-03-13 12:57:14 -04:00
parent 696d1f7f06
commit a2eb9e0c08
1 changed files with 11 additions and 10 deletions
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21
src/backend/optimizer/util/pathnode.c
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@ -254,8 +254,9 @@ add_path(RelOptInfo *parent_rel, Path *new_path)
{
bool accept_new = true; /* unless we find a superior old path */
ListCell *insert_after = NULL; /* where to insert new item */
ListCell *p1_prev = NULL;
ListCell *p1;
ListCell *p1_prev;
ListCell *p1_next;
/*
* This is a convenient place to check for query cancel --- no part of the
@ -267,14 +268,19 @@ add_path(RelOptInfo *parent_rel, Path *new_path)
* Loop to check proposed new path against old paths. Note it is possible
* for more than one old path to be tossed out because new_path dominates
* it.
*
* We can't use foreach here because the loop body may delete the current
* list cell.
*/
p1 = list_head(parent_rel->pathlist); /* cannot use foreach here */
while (p1 != NULL)
p1_prev = NULL;
for (p1 = list_head(parent_rel->pathlist); p1 != NULL; p1 = p1_next)
{
Path *old_path = (Path *) lfirst(p1);
bool remove_old = false; /* unless new proves superior */
int costcmp;
p1_next = lnext(p1);
/*
* As of Postgres 8.0, we use fuzzy cost comparison to avoid wasting
* cycles keeping paths that are really not significantly different in
@ -343,20 +349,15 @@ add_path(RelOptInfo *parent_rel, Path *new_path)
*/
if (!IsA(old_path, IndexPath))
pfree(old_path);
/* Advance list pointer */
if (p1_prev)
p1 = lnext(p1_prev);
else
p1 = list_head(parent_rel->pathlist);
/* p1_prev does not advance */
}
else
{
/* new belongs after this old path if it has cost >= old's */
if (costcmp >= 0)
insert_after = p1;
/* Advance list pointers */
/* p1_prev advances */
p1_prev = p1;
p1 = lnext(p1);
}
/*