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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2011-03-13 12:57:14 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2011-03-13 12:57:14 -0400 |
| commit | a2eb9e0c08ee73208b5419f5a53a6eba55809b92 (patch) | |
| tree | 53252c24d2dff6965b09615ae26303829792ac73 /src | |
| parent | 696d1f7f064402840a60b7177a838d1452ad13e6 (diff) | |
| download | postgresql-a2eb9e0c08ee73208b5419f5a53a6eba55809b92.tar.gz postgresql-a2eb9e0c08ee73208b5419f5a53a6eba55809b92.zip | |
Simplify list traversal logic in add_path().
Its mechanism for recovering after deleting the current list cell was
a bit klugy. Borrow the technique used in other places.
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/optimizer/util/pathnode.c | 21 |
1 files changed, 11 insertions, 10 deletions
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c index 1158f7715bc..b60c88d9251 100644 --- a/src/backend/optimizer/util/pathnode.c +++ b/src/backend/optimizer/util/pathnode.c @@ -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); } /* |