From 989adace3f19010f21009477afb5b50e1a4dd3c6 Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Tue, 31 Oct 2023 09:10:35 -0400 Subject: [PATCH] doc: 1-byte varlena headers can be used for user PLAIN storage This also updates some C comments. Reported-by: suchithjn22@gmail.com Discussion: https://postgr.es/m/167336599095.2667301.15497893107226841625@wrigleys.postgresql.org Author: Laurenz Albe (doc patch) Backpatch-through: 11 --- doc/src/sgml/storage.sgml | 4 +--- src/backend/access/common/heaptuple.c | 11 ++++++++++- src/backend/utils/adt/rangetypes.c | 3 ++- 3 files changed, 13 insertions(+), 5 deletions(-) diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml index 148fb1b49d..3ea4e5526d 100644 --- a/doc/src/sgml/storage.sgml +++ b/doc/src/sgml/storage.sgml @@ -456,9 +456,7 @@ for storing TOAST-able columns on disk: PLAIN prevents either compression or - out-of-line storage; furthermore it disables use of single-byte headers - for varlena types. - This is the only possible strategy for + out-of-line storage. This is the only possible strategy for columns of non-TOAST-able data types. diff --git a/src/backend/access/common/heaptuple.c b/src/backend/access/common/heaptuple.c index d6a4ddfd51..c52d40dce0 100644 --- a/src/backend/access/common/heaptuple.c +++ b/src/backend/access/common/heaptuple.c @@ -68,7 +68,16 @@ #include "utils/memutils.h" -/* Does att's datatype allow packing into the 1-byte-header varlena format? */ +/* + * Does att's datatype allow packing into the 1-byte-header varlena format? + * While functions that use TupleDescAttr() and assign attstorage = + * TYPSTORAGE_PLAIN cannot use packed varlena headers, functions that call + * TupleDescInitEntry() use typeForm->typstorage (TYPSTORAGE_EXTENDED) and + * can use packed varlena headers, e.g.: + * CREATE TABLE test(a VARCHAR(10000) STORAGE PLAIN); + * INSERT INTO test VALUES (repeat('A',10)); + * This can be verified with pageinspect. + */ #define ATT_IS_PACKABLE(att) \ ((att)->attlen == -1 && (att)->attstorage != TYPSTORAGE_PLAIN) /* Use this if it's already known varlena */ diff --git a/src/backend/utils/adt/rangetypes.c b/src/backend/utils/adt/rangetypes.c index d65e5625c7..24bad52923 100644 --- a/src/backend/utils/adt/rangetypes.c +++ b/src/backend/utils/adt/rangetypes.c @@ -2608,7 +2608,8 @@ range_contains_elem_internal(TypeCacheEntry *typcache, const RangeType *r, Datum * values into a range object. They are modeled after heaptuple.c's * heap_compute_data_size() and heap_fill_tuple(), but we need not handle * null values here. TYPE_IS_PACKABLE must test the same conditions as - * heaptuple.c's ATT_IS_PACKABLE macro. + * heaptuple.c's ATT_IS_PACKABLE macro. See the comments thare for more + * details. */ /* Does datatype allow packing into the 1-byte-header varlena format? */