diff options
| -rw-r--r-- | doc/src/sgml/catalogs.sgml | 48 |
1 files changed, 25 insertions, 23 deletions
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml index 32a51dbd8c6..c467c8bdae7 100644 --- a/doc/src/sgml/catalogs.sgml +++ b/doc/src/sgml/catalogs.sgml @@ -6885,6 +6885,8 @@ 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. + Also, <quote>advisory</> locks can be taken on numbers that have + user-defined meanings. </para> <table> @@ -6985,9 +6987,7 @@ <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. - For advisory locks it is used to distinguish the two key - spaces (1 for an int8 key, 2 for two int4 keys). + object is not a general database object </entry> </row> <row> @@ -6995,10 +6995,11 @@ <entry><type>smallint</type></entry> <entry></entry> <entry> - For a table column, this is the column number (the + Column number targeted by the lock (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 + table itself), + or zero if the target is some other general database object, + or null if the target is not a general database object </entry> </row> <row> @@ -7015,7 +7016,7 @@ <entry></entry> <entry> Process ID of the server process holding or awaiting this - lock. Null if the lock is held by a prepared transaction. + lock, or null if the lock is held by a prepared transaction </entry> </row> <row> @@ -7068,7 +7069,8 @@ <para> Advisory locks can be acquired on keys consisting of either a single - <type>bigint</type> value or two integer values. A <type>bigint</type> key is displayed with its + <type>bigint</type> value or two integer values. + A <type>bigint</type> key is displayed with its high-order half in the <structfield>classid</> column, its low-order half in the <structfield>objid</> column, and <structfield>objsubid</> equal to 1. Integer keys are displayed with the first key in the @@ -7079,21 +7081,6 @@ </para> <para> - The <structname>pg_locks</structname> view displays data from both the - regular lock manager and the predicate lock manager, which are - separate systems. When this view is accessed, the internal data - structures of each lock manager are momentarily locked, and copies are - made for the view to display. Each lock manager will therefore - produce a consistent set of results, but as we do not lock both lock - managers simultaneously, it is possible for locks to be taken or - released after we interrogate the regular lock manager and before we - interrogate the predicate lock manager. Each lock manager is only - locked for the minimum possible time so as to reduce the performance - impact of querying this view, but there could nevertheless be some - impact on database performance if it is frequently accessed. - </para> - - <para> <structname>pg_locks</structname> provides a global view of all locks in the database cluster, not only those relevant to the current database. Although its <structfield>relation</structfield> column can be joined @@ -7117,6 +7104,21 @@ but it continues to hold the locks it acquired while running.) </para> + <para> + The <structname>pg_locks</structname> view displays data from both the + regular lock manager and the predicate lock manager, which are + separate systems. When this view is accessed, the internal data + structures of each lock manager are momentarily locked, and copies are + made for the view to display. Each lock manager will therefore + produce a consistent set of results, but as we do not lock both lock + managers simultaneously, it is possible for locks to be taken or + released after we interrogate the regular lock manager and before we + interrogate the predicate lock manager. Each lock manager is only + locked for the minimum possible time so as to reduce the performance + impact of querying this view, but there could nevertheless be some + impact on database performance if it is frequently accessed. + </para> + </sect1> <sect1 id="view-pg-prepared-statements"> |