Commitfbaee69

committed

doc: 1-byte varlena headers can be used for user PLAIN storage

This also updates some C comments.Reported-by: suchithjn22@gmail.comDiscussion:https://postgr.es/m/167336599095.2667301.15497893107226841625@wrigleys.postgresql.orgAuthor: Laurenz Albe (doc patch)Backpatch-through: 11

1 parentb3c8d1d commitfbaee69Copy full SHA for fbaee69

File tree

+13

-5

lines changed

+13

-5

lines changed

Lines changed: 1 addition & 3 deletions

Original file line number	Diff line number	Diff line change
`@@ -452,9 +452,7 @@ for storing <acronym>TOAST</acronym>-able columns on disk:`
`452`	`452`	`<listitem>`
`453`	`453`	`<para>`
`454`	`454`	`<literal>PLAIN</literal> prevents either compression or`
`455`		`- out-of-line storage; furthermore it disables use of single-byte headers`
`456`		`- for varlena types.`
`457`		`- This is the only possible strategy for`
	`455`	`+ out-of-line storage. This is the only possible strategy for`
`458`	`456`	`columns of non-<acronym>TOAST</acronym>-able data types.`
`459`	`457`	`</para>`
`460`	`458`	`</listitem>`

Lines changed: 10 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -68,7 +68,16 @@`
`68`	`68`	`#include"utils/memutils.h"`
`69`	`69`
`70`	`70`
`71`		`-/* Does att's datatype allow packing into the 1-byte-header varlena format? */`
	`71`	`+/*`
	`72`	`+ * Does att's datatype allow packing into the 1-byte-header varlena format?`
	`73`	`+ * While functions that use TupleDescAttr() and assign attstorage =`
	`74`	`+ * TYPSTORAGE_PLAIN cannot use packed varlena headers, functions that call`
	`75`	`+ * TupleDescInitEntry() use typeForm->typstorage (TYPSTORAGE_EXTENDED) and`
	`76`	`+ * can use packed varlena headers, e.g.:`
	`77`	`+ * CREATE TABLE test(a VARCHAR(10000) STORAGE PLAIN);`
	`78`	`+ * INSERT INTO test VALUES (repeat('A',10));`
	`79`	`+ * This can be verified with pageinspect.`
	`80`	`+ */`
`72`	`81`	`#defineATT_IS_PACKABLE(att) \`
`73`	`82`	`((att)->attlen == -1 && (att)->attstorage != TYPSTORAGE_PLAIN)`
`74`	`83`	`/* Use this if it's already known varlena */`

Lines changed: 2 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -2384,7 +2384,8 @@ range_contains_elem_internal(TypeCacheEntry typcache, const RangeType r, Datum`
`2384`	`2384`	`* values into a range object. They are modeled after heaptuple.c's`
`2385`	`2385`	`* heap_compute_data_size() and heap_fill_tuple(), but we need not handle`
`2386`	`2386`	`* null values here. TYPE_IS_PACKABLE must test the same conditions as`
`2387`		`- * heaptuple.c's ATT_IS_PACKABLE macro.`
	`2387`	`+ * heaptuple.c's ATT_IS_PACKABLE macro. See the comments thare for more`
	`2388`	`+ * details.`
`2388`	`2389`	`*/`
`2389`	`2390`
`2390`	`2391`	`/* Does datatype allow packing into the 1-byte-header varlena format? */`

Comments

(0)