database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-09-02 04:21:28 +03:00
Code Activity

Use list_copy_head() instead of list_truncate(list_copy(...), ...)

Browse Source 
Truncating off the end of a freshly copied List is not a very efficient
way of copying the first N elements of a List.

In many of the cases that are updated here, the pattern was only being
used to remove the final element of a List.  That's about the best case
for it, but there were many instances where the truncate trimming the List
down much further.

4cc832f94 added list_copy_head(), so let's use it in cases where it's
useful.

Author: David Rowley
Discussion: https://postgr.es/m/1986787.1657666922%40sss.pgh.pa.us
This commit is contained in:
David Rowley
2022-07-13 15:03:47 +12:00
parent 50e4c280f0
commit c23e3e6beb
7 changed files with 25 additions and 30 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
src/backend/optimizer/plan/createplan.c
View File

@@ -1397,8 +1397,7 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
*/
if (tlist_was_changed && (flags & (CP_EXACT_TLIST | CP_SMALL_TLIST)))
{
tlist = list_truncate(list_copy(plan->plan.targetlist),
orig_tlist_length);
tlist = list_copy_head(plan->plan.targetlist, orig_tlist_length);
return inject_projection_plan((Plan *) plan, tlist,
plan->plan.parallel_safe);
}
@@ -1557,7 +1556,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
*/
if (tlist_was_changed && (flags & (CP_EXACT_TLIST | CP_SMALL_TLIST)))
{
tlist = list_truncate(list_copy(plan->targetlist), orig_tlist_length);
tlist = list_copy_head(plan->targetlist, orig_tlist_length);
return inject_projection_plan(plan, tlist, plan->parallel_safe);
}
else