Вся предоставленная на этом сервере информация собрана нами из разных источников. Если Вам кажется, что публикация каких-то документов нарушает чьи-либо авторские права, сообщите нам об этом.
Having introduced the basic extensibility concepts, we
can now take a look at how the catalogs are actually
laid out. You can skip this section for now, but some
later sections will be incomprehensible without the
information given here, so mark this page for later
reference.
All system catalogs have names that begin with
pg_.
The following classes contain information that may be
useful to the end user. (There are many other system
catalogs, but there should rarely be a reason to query
them directly.)
The Reference Manual gives a more detailed explanation
of these catalogs and their attributes. However,
The major Postgres system catalogs
shows the major entities and their relationships
in the system catalogs. (Attributes that do not refer
to other entities are not shown unless they are part of
a primary key.)
This diagram is more or less incomprehensible until you
actually start looking at the contents of the catalogs
and see how they relate to each other. For now, the
main things to take away from this diagram are as follows:
In several of the sections that follow, we will
present various join queries on the system
catalogs that display information we need to extend
the system. Looking at this diagram should make
some of these join queries (which are often
three- or four-way joins) more understandable,
because you will be able to see that the
attributes used in the queries form foreign keys
in other classes.
Many different features (classes, attributes,
functions, types, access methods, etc.) are
tightly integrated in this schema. A simple
create command may modify many of these catalogs.
Types and procedures
are central to the schema.
Note: We use the words procedure
and function more or less interchangably.
Nearly every catalog contains some reference to
instances in one or both of these classes. For
example, Postgres frequently uses type
signatures (e.g., of functions and operators) to
identify unique instances of other catalogs.
There are many attributes and relationships that
have obvious meanings, but there are many
(particularly those that have to do with access
methods) that do not. The relationships between
pg_am, pg_amop, pg_amproc, pg_operator and
pg_opclass are particularly hard to understand
and will be described in depth (in the section
on interfacing types and operators to indices)
after we have discussed basic extensions.
