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* ---------------- * pg_attribute definition. cpp turns this into * typedef struct FormData_pg_attribute * * If you change the following, make sure you change the structs for * system attributes in catalog/heap.c also. * ----------------
#define AttributeRelationId 1249
CATALOG(pg_attribute,1249) BKI_BOOTSTRAP BKI_WITHOUT_OIDS {
Oid attrelid; /* OID of relation containing this attribute */ NameData attname; /* name of attribute */
/* * atttypid is the OID of the instance in Catalog Class pg_type that * defines the data type of this attribute (e.g. int4). Information in * that instance is redundant with the attlen, attbyval, and attalign * attributes of this instance, so they had better match or Postgres will * fail. */ Oid atttypid;
/* * attstattarget is the target number of statistics datapoints to collect * during VACUUM ANALYZE of this column. A zero here indicates that we do * not wish to collect any stats about this column. A "-1" here indicates * that no value has been explicitly set for this column, so ANALYZE * should use the default setting. */ int4 attstattarget;
/* * attlen is a copy of the typlen field from pg_type for this attribute. * See atttypid comments above. */ int2 attlen;
/* * attnum is the "attribute number" for the attribute: A value that * uniquely identifies this attribute within its class. For user * attributes, Attribute numbers are greater than 0 and not greater than * the number of attributes in the class. I.e. if the Class pg_class says * that Class XYZ has 10 attributes, then the user attribute numbers in * Class pg_attribute must be 1-10. * * System attributes have attribute numbers less than 0 that are unique * within the class, but not constrained to any particular range. * * Note that (attnum - 1) is often used as the index to an array. */ int2 attnum;
/* * attndims is the declared number of dimensions, if an array type, * otherwise zero. */ int4 attndims;
/* * fastgetattr() uses attcacheoff to cache byte offsets of attributes in * heap tuples. The value actually stored in pg_attribute (-1) indicates * no cached value. But when we copy these tuples into a tuple * descriptor, we may then update attcacheoff in the copies. This speeds * up the attribute walking process. */ int4 attcacheoff;
/* * atttypmod records type-specific data supplied at table creation time * (for example, the max length of a varchar field). It is passed to * type-specific input and output functions as the third argument. The * value will generally be -1 for types that do not need typmod. */ int4 atttypmod;
/* * attbyval is a copy of the typbyval field from pg_type for this * attribute. See atttypid comments above. */ bool attbyval;
/*----------
* attstorage tells for VARLENA attributes, what the heap access
* methods can do to it if a given tuple doesn't fit into a page.
* Possible values are
* 'p': Value must be stored plain always
* 'e': Value can be stored in "secondary" relation (if relation
* has one, see pg_class.reltoastrelid)
* 'm': Value can be stored compressed inline
* 'x': Value can be stored compressed inline or in "secondary"
* Note that 'm' fields can also be moved out to secondary storage,
* but only as a last resort ('e' and 'x' fields are moved first).
*----------
*/
char attstorage;
/* * attalign is a copy of the typalign field from pg_type for this * attribute. See atttypid comments above. */ char attalign;
/* This flag represents the "NOT NULL" constraint */ bool attnotnull;
/* Has DEFAULT value or not */ bool atthasdef;
/* Is dropped (ie, logically invisible) or not */ bool attisdropped;
/* Has a local definition (hence, do not drop when attinhcount is 0) */ bool attislocal;
/* Number of times inherited from direct parent relation(s) */ int4 attinhcount;
} FormData_pg_attribute;
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