51.11 pg_class
版本:11
The catalog pg_class
catalogs tables and most everything else that has columns or is otherwise similar to a table. This includes indexes (but see also pg_index
), sequences (but see also pg_sequence
), views, materialized views, composite types, and TOAST tables; see relkind
. Below, when we mean all of these kinds of objects we speak of “relations”. Not all columns are meaningful for all relation types.
Table 51.11. pg_class
Columns
pg_class
ColumnsSeveral of the Boolean flags in pg_class
are maintained lazily: they are guaranteed to be true if that's the correct state, but may not be reset to false immediately when the condition is no longer true. For example, relhasindex
is set by CREATE INDEX
, but it is never cleared by DROP INDEX
. Instead, VACUUM
clears relhasindex
if it finds the table has no indexes. This arrangement avoids race conditions and improves concurrency.\
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