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

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

diff --git a/src/backend/catalog/objectaddress.c b/src/backend/catalog/objectaddress.c
index 2d21db469012dfd30568a03eebf4109dfb30feb5..6080ff8f5f74c5e1d4243508b2d018227785f802 100644 (file)
--- a/src/backend/catalog/objectaddress.c
+++ b/src/backend/catalog/objectaddress.c
@@ -1453,7 +1453,7 @@ get_object_address_relobject(ObjectType objtype, List *object,
                 errmsg("must specify relation and object name")));
 
    /* Extract relation name and open relation. */
-   relname = list_truncate(list_copy(object), nnames - 1);
+   relname = list_copy_head(object, nnames - 1);
    relation = table_openrv_extended(makeRangeVarFromNameList(relname),
                                     AccessShareLock,
                                     missing_ok);
@@ -1528,7 +1528,7 @@ get_object_address_attribute(ObjectType objtype, List *object,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("column name must be qualified")));
    attname = strVal(llast(object));
-   relname = list_truncate(list_copy(object), list_length(object) - 1);
+   relname = list_copy_head(object, list_length(object) - 1);
    /* XXX no missing_ok support here */
    relation = relation_openrv(makeRangeVarFromNameList(relname), lockmode);
    reloid = RelationGetRelid(relation);
@@ -1581,7 +1581,7 @@ get_object_address_attrdef(ObjectType objtype, List *object,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("column name must be qualified")));
    attname = strVal(llast(object));
-   relname = list_truncate(list_copy(object), list_length(object) - 1);
+   relname = list_copy_head(object, list_length(object) - 1);
    /* XXX no missing_ok support here */
    relation = relation_openrv(makeRangeVarFromNameList(relname), lockmode);
    reloid = RelationGetRelid(relation);
@@ -1715,7 +1715,7 @@ get_object_address_opf_member(ObjectType objtype,
     * address.  The rest can be used directly by get_object_address_opcf().
     */
    membernum = atoi(strVal(llast(linitial(object))));
-   copy = list_truncate(list_copy(linitial(object)), list_length(linitial(object)) - 1);
+   copy = list_copy_head(linitial(object), list_length(linitial(object)) - 1);
 
    /* no missing_ok support here */
    famaddr = get_object_address_opcf(OBJECT_OPFAMILY, copy, false);

diff --git a/src/backend/commands/dropcmds.c b/src/backend/commands/dropcmds.c
index c9b5732448e980c0534326d7a626c0ff81cf379d..26157eb4e3f58d7d150e17f61ec3d93917dff831 100644 (file)
--- a/src/backend/commands/dropcmds.c
+++ b/src/backend/commands/dropcmds.c
@@ -145,8 +145,7 @@ owningrel_does_not_exist_skipping(List *object, const char **msg, char **name)
    List       *parent_object;
    RangeVar   *parent_rel;
 
-   parent_object = list_truncate(list_copy(object),
-                                 list_length(object) - 1);
+   parent_object = list_copy_head(object, list_length(object) - 1);
 
    if (schema_does_not_exist_skipping(parent_object, msg, name))
        return true;
@@ -419,8 +418,8 @@ does_not_exist_skipping(ObjectType objtype, Node *object)
            {
                msg = gettext_noop("trigger \"%s\" for relation \"%s\" does not exist, skipping");
                name = strVal(llast(castNode(List, object)));
-               args = NameListToString(list_truncate(list_copy(castNode(List, object)),
-                                                     list_length(castNode(List, object)) - 1));
+               args = NameListToString(list_copy_head(castNode(List, object),
+                                                      list_length(castNode(List, object)) - 1));
            }
            break;
        case OBJECT_POLICY:
@@ -428,8 +427,8 @@ does_not_exist_skipping(ObjectType objtype, Node *object)
            {
                msg = gettext_noop("policy \"%s\" for relation \"%s\" does not exist, skipping");
                name = strVal(llast(castNode(List, object)));
-               args = NameListToString(list_truncate(list_copy(castNode(List, object)),
-                                                     list_length(castNode(List, object)) - 1));
+               args = NameListToString(list_copy_head(castNode(List, object),
+                                                      list_length(castNode(List, object)) - 1));
            }
            break;
        case OBJECT_EVENT_TRIGGER:
@@ -441,8 +440,8 @@ does_not_exist_skipping(ObjectType objtype, Node *object)
            {
                msg = gettext_noop("rule \"%s\" for relation \"%s\" does not exist, skipping");
                name = strVal(llast(castNode(List, object)));
-               args = NameListToString(list_truncate(list_copy(castNode(List, object)),
-                                                     list_length(castNode(List, object)) - 1));
+               args = NameListToString(list_copy_head(castNode(List, object),
+                                                      list_length(castNode(List, object)) - 1));
            }
            break;
        case OBJECT_FDW:

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index 48d9d43dac692283a179a2e076411458bcbdb345..b0b211891c3ebecf3b37ce70aedb0be4d7cd6c7c 100644 (file)
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -1620,7 +1620,7 @@ process_owned_by(Relation seqrel, List *owned_by, bool for_identity)
        RangeVar   *rel;
 
        /* Separate relname and attr name */
-       relname = list_truncate(list_copy(owned_by), nnames - 1);
+       relname = list_copy_head(owned_by, nnames - 1);
        attrname = strVal(llast(owned_by));
 
        /* Open and lock rel to ensure it won't go away meanwhile */

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index e9342097e52bf6e97f336c06d6361aac50f212b0..358bb2aed6f48f7d044bbe2622709c4c2f7179d9 100644 (file)
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -2053,9 +2053,8 @@ accumulate_append_subpath(Path *path, List **subpaths, List **special_subpaths)
            *subpaths = list_concat(*subpaths,
                                    list_copy_tail(apath->subpaths,
                                                   apath->first_partial_path));
-           new_special_subpaths =
-               list_truncate(list_copy(apath->subpaths),
-                             apath->first_partial_path);
+           new_special_subpaths = list_copy_head(apath->subpaths,
+                                                 apath->first_partial_path);
            *special_subpaths = list_concat(*special_subpaths,
                                            new_special_subpaths);
            return;
@@ -3086,8 +3085,8 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel,
                                           root->query_pathkeys);
        else if (npathkeys > 0)
            useful_pathkeys_list = lappend(useful_pathkeys_list,
-                                          list_truncate(list_copy(root->query_pathkeys),
-                                                        npathkeys));
+                                          list_copy_head(root->query_pathkeys,
+                                                         npathkeys));
    }
 
    return useful_pathkeys_list;

diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 0ef70ad7f1193787b1979566d75ce6c7bf2c2d75..7d176e7b00aba5730945f3bfa23a111dcbe64613 100644 (file)
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -3026,14 +3026,12 @@ expand_indexqual_rowcompare(PlannerInfo *root,
 
            rc->rctype = (RowCompareType) op_strategy;
            rc->opnos = new_ops;
-           rc->opfamilies = list_truncate(list_copy(clause->opfamilies),
-                                          matching_cols);
-           rc->inputcollids = list_truncate(list_copy(clause->inputcollids),
-                                            matching_cols);
-           rc->largs = list_truncate(copyObject(var_args),
-                                     matching_cols);
-           rc->rargs = list_truncate(copyObject(non_var_args),
-                                     matching_cols);
+           rc->opfamilies = list_copy_head(clause->opfamilies,
+                                           matching_cols);
+           rc->inputcollids = list_copy_head(clause->inputcollids,
+                                             matching_cols);
+           rc->largs = list_copy_head(var_args, matching_cols);
+           rc->rargs = list_copy_head(non_var_args, matching_cols);
            iclause->indexquals = list_make1(make_simple_restrictinfo(root,
                                                                      (Expr *) rc));
        }

diff --git a/src/backend/optimizer/path/pathkeys.c b/src/backend/optimizer/path/pathkeys.c
index 985b5d8de9bd97a41b701a2a9b3d64a579ee88b7..b5d6c977eef60a05f3f9afd02edf4c8c3c803339 100644 (file)
--- a/src/backend/optimizer/path/pathkeys.c
+++ b/src/backend/optimizer/path/pathkeys.c
@@ -2464,7 +2464,7 @@ truncate_useless_pathkeys(PlannerInfo *root,
    else if (nuseful == list_length(pathkeys))
        return pathkeys;
    else
-       return list_truncate(list_copy(pathkeys), nuseful);
+       return list_copy_head(pathkeys, nuseful);
 }
 
 /*

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 76606faa3e4918339769d0f93d33f7ba62d0815f..e37f2933eb8d52a05412db512d526ad85555cb99 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -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