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