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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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2
src/backend/commands/sequence.c
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@ -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 */