diff options
Diffstat (limited to 'doc/src/sgml/monitoring.sgml')
| -rw-r--r-- | doc/src/sgml/monitoring.sgml | 88 |
1 files changed, 56 insertions, 32 deletions
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index e759789c1f4..6e801174e88 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -1,5 +1,5 @@ <!-- -$Header: /cvsroot/pgsql/doc/src/sgml/monitoring.sgml,v 1.12 2002/08/20 04:47:52 momjian Exp $ +$Header: /cvsroot/pgsql/doc/src/sgml/monitoring.sgml,v 1.13 2002/08/31 17:14:27 tgl Exp $ --> <chapter id="monitoring"> @@ -593,22 +593,25 @@ FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS S; <note> <para> - When the <literal>pg_locks</literal> view is accessed, an - exclusive lock on an internal lock manager data structure must be - acquired to ensure that the data produced by the view is - consistent. The lock held on this structure conflicts with normal - database operations, and can therefore have an effect on overall - database performance. Nevertheless, the performance impact of - accessing this view should be minimal in most situations. + When the <literal>pg_locks</literal> view is accessed, the + internal lock manager data structures are momentarily locked, + and a copy is made for the view to display. This ensures that + the view produces a consistent set of results, while not blocking + normal lock manager operations longer than necessary. Nonetheless + there could be some impact on database performance if this view is + examined often. </para> </note> <para> - The <literal>pg_locks</literal> view contains one row per - lock. This means that if there are multiple locks on a single - relation (which may or may not conflict with one another), a - single relation may show up many times. Furthermore, only - table-level locks are displayed (not row-level ones). + The <literal>pg_locks</literal> view contains one row per lockable + object and requested lock mode. Thus, the same lockable object + may appear many times, if multiple transactions are holding or + waiting for locks on it. A lockable object is either a relation + or a transaction ID. (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.) </para> <table> @@ -627,31 +630,50 @@ FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS S; <row> <entry><structfield>relation</structfield></entry> <entry><type>oid</type></entry> - <entry>The OID of the locked relation. When querying - <literal>pg_locks</literal>, this column can be joined with the - <literal>pg_class</literal> system catalog to get more - information on the locked relation.</entry> + <entry>The OID of the locked relation, or NULL if the lockable + object is a transaction ID. This column can be joined + with the <literal>pg_class</literal> system catalog to get more + information on the locked relation. Note however that this will + only work for relations in the current database (those for which + the <structfield>database</structfield> column is either the + current database's OID or zero). + </entry> </row> <row> <entry><structfield>database</structfield></entry> <entry><type>oid</type></entry> <entry>The OID of the database in which the locked relation - exists. If the lock is on a globally-shared object, this value - will be 0. When querying <literal>pg_locks</literal>, this - column can be joined with the <literal>pg_database</literal> - system catalog to get more information on the locked object's - database.</entry> + exists, or NULL if the lockable object is a transaction ID. + If the lock is on a globally-shared table, this field will be + zero. This + column can be joined with the <literal>pg_database</literal> + system catalog to get more information on the locked object's + database. + </entry> </row> <row> - <entry><structfield>backendpid</structfield></entry> + <entry><structfield>transaction</structfield></entry> + <entry><type>xid</type></entry> + <entry>The ID of a transaction, or NULL if the lockable object + is a relation. Every transaction holds ExclusiveLock on its + transaction ID for its entire duration. If one transaction finds + it necessary to wait specifically for another transaction, it + does so by attempting to acquire ShareLock on the other transaction + ID. That will succeed only when the other transaction terminates + and releases its locks. + </entry> + </row> + + <row> + <entry><structfield>pid</structfield></entry> <entry><type>int4</type></entry> <entry>The process ID of the <productname>PostgreSQL</productname> backend that has acquired or is attempting to acquire the lock. If you have enabled the statistics collector, this column can be joined - with the <literal>pg_stat_activity</literal> view to access + with the <literal>pg_stat_activity</literal> view to get more information on the backend holding or waiting to hold the lock.</entry> </row> @@ -659,7 +681,8 @@ FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS S; <row> <entry><structfield>mode</structfield></entry> <entry><type>text</type></entry> - <entry>The mode of the lock. For more information on the + <entry>The mode of the requested or held lock on the lockable + object. For more information on the different lock modes available in <productname>PostgreSQL</productname>, refer to the <citetitle>User's Guide</citetitle>.</entry> @@ -667,13 +690,14 @@ FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS S; <row> <entry><structfield>isgranted</structfield></entry> - <entry><type>text</type></entry> - <entry>A boolean column indicating whether or not this - particular lock has been granted. If the lock has not been - granted, the backend atempting to acquire it will sleep until - the lock is released (or a deadlock situation is detected). A - single backend can be waiting to acquire at most one lock at - any given time.</entry> + <entry><type>bool</type></entry> + <entry>True if this lock has been granted (is held by this + backend). False indicates that this backend is currently + waiting to acquire this lock, which implies that some other + backend is holding a conflicting lock mode on the same lockable + object. This backend will sleep until the other lock is released + (or a deadlock situation is detected). A single backend can be + waiting to acquire at most one lock at a time.</entry> </row> </tbody> </tgroup> |