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Extend the pg_locks system view so that it can fully display all lock

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types, as per recent discussion.
This commit is contained in:
Tom Lane
2005-05-17 21:46:11 +00:00
parent 4e7d6f5349
commit a9c4c9cd52
7 changed files with 207 additions and 52 deletions
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113
doc/src/sgml/catalogs.sgml
View File

@ -1,6 +1,6 @@
<!--
Documentation of the system catalogs, directed toward PostgreSQL developers
$PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.101 2005/05/06 14:28:53 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.102 2005/05/17 21:46:09 tgl Exp $
-->
<chapter id="catalogs">
@ -4040,15 +4040,18 @@
lockable object may
appear many times, if multiple transactions are holding or waiting
for locks on it. However, an object that currently has no locks on it
will not appear at all. A lockable object is either a relation (e.g., a
table) or a transaction ID.
will not appear at all.
</para>
<para>
Note that this view includes only table-level
locks, not row-level ones. If a transaction is waiting for a
row-level lock, it will appear in the view as waiting for the
transaction ID of the current holder of that row lock.
There are several distinct types of lockable objects:
whole relations (e.g., tables), individual pages of relations,
individual tuples of relations,
transaction IDs,
and general database objects (identified by class OID and object OID,
in the same way as in <structname>pg_description</structname> or
<structname>pg_depend</structname>). Also, the right to extend a
relation is represented as a separate lockable object.
</para>
<table>
@ -4065,12 +4068,18 @@
</thead>
<tbody>
<row>
<entry><structfield>relation</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry><structfield>locktype</structfield></entry>
<entry><type>text</type></entry>
<entry></entry>
<entry>
OID of the locked relation, or NULL if the lockable object
is a transaction ID
type of the lockable object:
<literal>relation</>,
<literal>extend</>,
<literal>page</>,
<literal>tuple</>,
<literal>transaction</>,
<literal>object</>, or
<literal>userlock</>
</entry>
</row>
<row>
@ -4078,9 +4087,35 @@
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>
<entry>
OID of the database in which the locked relation exists, or
zero if the locked relation is a globally-shared table, or
NULL if the lockable object is a transaction ID
OID of the database in which the object exists, or
zero if the object is a globally-shared object, or
NULL if the object is a transaction ID
</entry>
</row>
<row>
<entry><structfield>relation</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>
OID of the relation, or NULL if the object is not
a relation or part of a relation
</entry>
</row>
<row>
<entry><structfield>page</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>
page number within the relation, or NULL if the object
is not a tuple or relation page
</entry>
</row>
<row>
<entry><structfield>tuple</structfield></entry>
<entry><type>smallint</type></entry>
<entry></entry>
<entry>
tuple number within the page, or NULL if the object is not a tuple
</entry>
</row>
<row>
@ -4088,14 +4123,43 @@
<entry><type>xid</type></entry>
<entry></entry>
<entry>
ID of a transaction, or NULL if the lockable object is a relation
ID of a transaction, or NULL if the object is not a transaction ID
</entry>
</row>
<row>
<entry><structfield>classid</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
<entry>
OID of the system catalog containing the object, or NULL if the
object is not a general database object
</entry>
</row>
<row>
<entry><structfield>objid</structfield></entry>
<entry><type>oid</type></entry>
<entry>any OID column</entry>
<entry>
OID of the object within its system catalog, or NULL if the
object is not a general database object
</entry>
</row>
<row>
<entry><structfield>objsubid</structfield></entry>
<entry><type>smallint</type></entry>
<entry></entry>
<entry>
For a table column, this is the column number (the
<structfield>classid</> and <structfield>objid</> refer to the
table itself). For all other object types, this column is
zero. NULL if the object is not a general database object
</entry>
</row>
<row>
<entry><structfield>pid</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>process ID of a server process holding or awaiting this
<entry>process ID of the server process holding or awaiting this
lock</entry>
</row>
<row>
@ -4133,6 +4197,21 @@
terminates and releases its locks.
</para>
<para>
Although tuples are a lockable type of object,
information about row-level locks is stored on disk, not in memory,
and therefore row-level locks normally do not appear in this view.
If a transaction is waiting for a
row-level lock, it will usually appear in the view as waiting for the
transaction ID of the current holder of that row lock.
</para>
<para>
If user-defined locks are in use, they are displayed using the columns
for general database objects. However, the actual meaning of the lock
fields in such cases is up to the user.
</para>
<para>
When the <structname>pg_locks</structname> view is accessed, the
internal lock manager data structures are momentarily locked, and