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Make attstattarget nullable

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This changes the pg_attribute field attstattarget into a nullable
field in the variable-length part of the row.  If no value is set by
the user for attstattarget, it is now null instead of previously -1.
This saves space in pg_attribute and tuple descriptors for most
practical scenarios.  (ATTRIBUTE_FIXED_PART_SIZE is reduced from 108
to 104.)  Also, null is the semantically more correct value.

The ANALYZE code internally continues to represent the default
statistics target by -1, so that that code can avoid having to deal
with null values.  But that is now contained to the ANALYZE code.
Only the DDL code deals with attstattarget possibly null.

For system columns, the field is now always null.  The ANALYZE code
skips system columns anyway.

To set a column's statistics target to the default value, the new
command form ALTER TABLE ... SET STATISTICS DEFAULT can be used.  (SET
STATISTICS -1 still works.)

Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://www.postgresql.org/message-id/flat/4da8d211-d54d-44b9-9847-f2a9f1184c76@eisentraut.org
This commit is contained in:
Peter Eisentraut
2024-01-13 18:14:53 +01:00
parent 45da69371e
commit 4f622503d6
16 changed files with 115 additions and 89 deletions
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1
src/include/utils/lsyscache.h
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@@ -90,7 +90,6 @@ extern Oid get_opfamily_proc(Oid opfamily, Oid lefttype, Oid righttype,
int16 procnum);
extern char *get_attname(Oid relid, AttrNumber attnum, bool missing_ok);
extern AttrNumber get_attnum(Oid relid, const char *attname);
extern int get_attstattarget(Oid relid, AttrNumber attnum);
extern char get_attgenerated(Oid relid, AttrNumber attnum);
extern Oid get_atttype(Oid relid, AttrNumber attnum);
extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,