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

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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
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15
src/backend/commands/dropcmds.c
View File

@@ -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:

2
src/backend/commands/sequence.c
View File

@@ -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 */