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Provide much better wait information in pg_stat_activity.
When a process is waiting for a heavyweight lock, we will now indicate the type of heavyweight lock for which it is waiting. Also, you can now see when a process is waiting for a lightweight lock - in which case we will indicate the individual lock name or the tranche, as appropriate - or for a buffer pin. Amit Kapila, Ildus Kurbangaliev, reviewed by me. Lots of helpful discussion and suggestions by many others, including Alexander Korotkov, Vladimir Borodin, and many others.
This commit is contained in:
Robert Haas
@ -632,10 +632,56 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
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<entry><type>timestamp with time zone</></entry>
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<entry>Time when the <structfield>state</> was last changed</entry>
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</row>
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<row>
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<entry><structfield>wait_event_type</></entry>
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<entry><type>text</></entry>
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<entry>The type of event for which the backend is waiting, if any;
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otherwise NULL. Possible values are:
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<itemizedlist>
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<listitem>
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<para>
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<literal>LWLockNamed</>: The backend is waiting for a specific named
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lightweight lock. Each such lock protects a particular data
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structure in shared memory. <literal>wait_event</> will contain
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the name of the lightweight lock.
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>LWLockTranche</>: The backend is waiting for one of a
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group of related lightweight locks. All locks in the group perform
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a similar function; <literal>wait_event</> will identify the general
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purpose of locks in that group.
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>Lock</>: The backend is waiting for a heavyweight lock.
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Heayweight locks, also known as lock manager locks or simply locks,
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primarily protect SQL-visible objects such as tables. However,
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they are also used to ensure mutual exclusion for certain internal
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operations such as relation extension. <literal>wait_event</> will
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identify the type of lock awaited.
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>BufferPin</>: The server process is waiting to access to
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a data buffer during a period when no other process can be
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examining that buffer. Buffer pin waits can be protracted if
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another process holds an open cursor which last read data from the
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buffer in question.
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</para>
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</listitem>
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</itemizedlist>
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</entry>
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</row>
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<row>
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<entry><structfield>waiting</></entry>
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<entry><type>boolean</></entry>
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<entry>True if this backend is currently waiting on a lock</entry>
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<entry><structfield>wait_event</></entry>
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<entry><type>text</></entry>
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<entry>Wait event name if backend is currently waiting, otherwise NULL.
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See <xref linkend="wait-event-table"> for details.
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</entry>
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</row>
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<row>
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<entry><structfield>state</></entry>
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@ -712,15 +758,351 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
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<note>
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<para>
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The <structfield>waiting</> and <structfield>state</> columns are
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The <structfield>wait_event</> and <structfield>state</> columns are
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independent. If a backend is in the <literal>active</> state,
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it may or may not be <literal>waiting</>. If the state is
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<literal>active</> and <structfield>waiting</> is true, it means
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that a query is being executed, but is being blocked by a lock
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somewhere in the system.
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it may or may not be <literal>waiting</> on some event. If the state
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is <literal>active</> and <structfield>wait_event</> is non-null, it
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means that a query is being executed, but is being blocked somewhere
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in the system.
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</para>
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</note>
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<table id="wait-event-table" xreflabel="wait_event">
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<title><structname>wait_event</structname> Description</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>Wait Event Type</entry>
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<entry>Wait Event Name</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry morerows="40"><literal>LWLockNamed</></entry>
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<entry><literal>ShmemIndexLock</></entry>
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<entry>Waiting to find or allocate space in shared memory.</entry>
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</row>
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<row>
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<entry><literal>OidGenLock</></entry>
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<entry>Waiting to allocate or assign an OID.</entry>
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</row>
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<row>
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<entry><literal>XidGenLock</></entry>
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<entry>Waiting to allocate or assign a transaction id.</entry>
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</row>
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<row>
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<entry><literal>ProcArrayLock</></entry>
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<entry>Waiting to get a snapshot or clearing a transaction id at
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transaction end.</entry>
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</row>
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<row>
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<entry><literal>SInvalReadLock</></entry>
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<entry>Waiting to retrieve or remove messages from shared invalidation
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queue.</entry>
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</row>
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<row>
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<entry><literal>SInvalWriteLock</></entry>
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<entry>Waiting to add a message in shared invalidation queue.</entry>
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</row>
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<row>
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<entry><literal>WALBufMappingLock</></entry>
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<entry>Waiting to replace a page in WAL buffers.</entry>
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</row>
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<row>
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<entry><literal>WALWriteLock</></entry>
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<entry>Waiting for WAL buffers to be written to disk.</entry>
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</row>
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<row>
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<entry><literal>ControlFileLock</></entry>
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<entry>Waiting to read or update the control file or creation of a
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new WAL file.</entry>
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</row>
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<row>
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<entry><literal>CheckpointLock</></entry>
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<entry>Waiting to perform checkpoint.</entry>
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</row>
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<row>
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<entry><literal>CLogControlLock</></entry>
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<entry>Waiting to read or update transaction status.</entry>
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</row>
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<row>
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<entry><literal>SubtransControlLock</></entry>
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<entry>Waiting to read or update sub-transaction information.</entry>
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</row>
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<row>
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<entry><literal>MultiXactGenLock</></entry>
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<entry>Waiting to read or update shared multixact state.</entry>
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</row>
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<row>
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<entry><literal>MultiXactOffsetControlLock</></entry>
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<entry>Waiting to read or update multixact offset mappings.</entry>
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</row>
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<row>
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<entry><literal>MultiXactMemberControlLock</></entry>
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<entry>Waiting to read or update multixact member mappings.</entry>
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</row>
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<row>
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<entry><literal>RelCacheInitLock</></entry>
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<entry>Waiting to read or write relation cache initialization
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file.</entry>
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</row>
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<row>
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<entry><literal>CheckpointerCommLock</></entry>
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<entry>Waiting to manage fsync requests.</entry>
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</row>
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<row>
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<entry><literal>TwoPhaseStateLock</></entry>
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<entry>Waiting to read or update the state of prepared transactions.</entry>
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</row>
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<row>
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<entry><literal>TablespaceCreateLock</></entry>
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<entry>Waiting to create or drop the tablespace.</entry>
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</row>
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<row>
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<entry><literal>BtreeVacuumLock</></entry>
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<entry>Waiting to read or update vacuum-related information for a
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Btree index.</entry>
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</row>
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<row>
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<entry><literal>AddinShmemInitLock</></entry>
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<entry>Waiting to manage space allocation in shared memory.</entry>
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</row>
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<row>
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<entry><literal>AutovacuumLock</></entry>
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<entry>Autovacuum worker or launcher waiting to update or
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read the current state of autovacuum workers.</entry>
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</row>
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<row>
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<entry><literal>AutovacuumScheduleLock</></entry>
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<entry>Waiting to ensure that the table it has selected for a vacuum
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still needs vacuuming.
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</entry>
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</row>
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<row>
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<entry><literal>SyncScanLock</></entry>
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<entry>Waiting to get the start location of a scan on a table for
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synchronized scans.</entry>
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</row>
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<row>
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<entry><literal>RelationMappingLock</></entry>
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<entry>Waiting to update the relation map file used to store catalog
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to filenode mapping.
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</entry>
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</row>
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<row>
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<entry><literal>AsyncCtlLock</></entry>
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<entry>Waiting to read or update shared notification state.</entry>
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</row>
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<row>
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<entry><literal>AsyncQueueLock</></entry>
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<entry>Waiting to read or update notification messages.</entry>
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</row>
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<row>
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<entry><literal>SerializableXactHashLock</></entry>
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<entry>Waiting to retrieve or store information about serializable
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transactions.</entry>
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</row>
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<row>
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<entry><literal>SerializableFinishedListLock</></entry>
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<entry>Waiting to access the list of finished serializable
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transactions.</entry>
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</row>
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<row>
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<entry><literal>SerializablePredicateLockListLock</></entry>
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<entry>Waiting to perform an operation on a list of locks held by
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serializable transactions.</entry>
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</row>
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<row>
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<entry><literal>OldSerXidLock</></entry>
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<entry>Waiting to read or record conflicting serializable
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transactions.</entry>
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</row>
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<row>
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<entry><literal>SyncRepLock</></entry>
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<entry>Waiting to read or update information about synchronous
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replicas.</entry>
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</row>
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<row>
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<entry><literal>BackgroundWorkerLock</></entry>
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<entry>Waiting to read or update background worker state.</entry>
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</row>
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<row>
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<entry><literal>DynamicSharedMemoryControlLock</></entry>
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<entry>Waiting to read or update dynamic shared memory state.</entry>
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</row>
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<row>
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<entry><literal>AutoFileLock</></entry>
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<entry>Waiting to update the <filename>postgresql.auto.conf</> file.</entry>
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</row>
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<row>
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<entry><literal>ReplicationSlotAllocationLock</></entry>
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<entry>Waiting to allocate or free a replication slot.</entry>
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</row>
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<row>
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<entry><literal>ReplicationSlotControlLock</></entry>
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<entry>Waiting to read or update replication slot state.</entry>
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</row>
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<row>
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<entry><literal>CommitTsControlLock</></entry>
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<entry>Waiting to read or update transaction commit timestamps.</entry>
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</row>
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<row>
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<entry><literal>CommitTsLock</></entry>
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<entry>Waiting to read or update the last value set for the
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transaction timestamp.</entry>
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</row>
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<row>
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<entry><literal>ReplicationOriginLock</></entry>
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<entry>Waiting to setup, drop or use replication origin.</entry>
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</row>
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<row>
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<entry><literal>MultiXactTruncationLock</></entry>
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<entry>Waiting to read or truncate multixact information.</entry>
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</row>
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<row>
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<entry morerows="15"><literal>LWLockTranche</></entry>
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<entry><literal>clog</></entry>
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<entry>Waiting for I/O on a clog (transcation status) buffer.</entry>
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</row>
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<row>
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<entry><literal>commit_timestamp</></entry>
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<entry>Waiting for I/O on commit timestamp buffer.</entry>
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</row>
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<row>
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<entry><literal>subtrans</></entry>
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<entry>Waiting for I/O a subtransaction buffer.</entry>
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</row>
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<row>
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<entry><literal>multixact_offset</></entry>
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<entry>Waiting for I/O on a multixact offset buffer.</entry>
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</row>
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<row>
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<entry><literal>multixact_member</></entry>
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<entry>Waiting for I/O on a multixact_member buffer.</entry>
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</row>
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<row>
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<entry><literal>async</></entry>
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<entry>Waiting for I/O on an async (notify) buffer.</entry>
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</row>
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<row>
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<entry><literal>oldserxid</></entry>
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<entry>Waiting to I/O on an oldserxid buffer.</entry>
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</row>
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<row>
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<entry><literal>wal_insert</></entry>
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<entry>Waiting to insert WAL into a memory buffer.</entry>
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</row>
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<row>
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<entry><literal>buffer_content</></entry>
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<entry>Waiting to read or write a data page in memory.</entry>
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</row>
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<row>
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<entry><literal>buffer_io</></entry>
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<entry>Waiting for I/O on a data page.</entry>
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</row>
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<row>
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<entry><literal>replication_origin</></entry>
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<entry>Waiting to read or update the replication progress.</entry>
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</row>
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<row>
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<entry><literal>replication_slot_io</></entry>
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<entry>Waiting for I/O on a replication slot.</entry>
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</row>
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<row>
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<entry><literal>proc</></entry>
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<entry>Waiting to read or update the fast-path lock information.</entry>
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</row>
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<row>
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<entry><literal>buffer_mapping</></entry>
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<entry>Waiting to associate a data block with a buffer in the buffer
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pool.</entry>
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</row>
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<row>
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<entry><literal>lock_manager</></entry>
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<entry>Waiting to add or examine locks for backends, or waiting to
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join or exit a locking group (used by parallel query).</entry>
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</row>
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<row>
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<entry><literal>predicate_lock_manager</></entry>
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<entry>Waiting to add or examine predicate lock information.</entry>
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</row>
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<row>
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<entry morerows="9"><literal>Lock</></entry>
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<entry><literal>relation</></entry>
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<entry>Waiting to acquire a lock on a relation.</entry>
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</row>
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<row>
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<entry><literal>extend</></entry>
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<entry>Waiting to extend a relation.</entry>
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</row>
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<row>
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<entry><literal>page</></entry>
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<entry>Waiting to acquire a lock on page of a relation.</entry>
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</row>
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<row>
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<entry><literal>tuple</></entry>
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<entry>Waiting to acquire a lock on a tuple.</entry>
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</row>
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<row>
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<entry><literal>transactionid</></entry>
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<entry>Waiting for a transaction to finish.</entry>
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</row>
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<row>
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<entry><literal>virtualxid</></entry>
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<entry>Waiting to acquire a virtual xid lock.</entry>
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</row>
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<row>
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<entry><literal>speculative token</></entry>
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<entry>Waiting to acquire a speculative insertion lock.</entry>
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</row>
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<row>
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<entry><literal>object</></entry>
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<entry>Waiting to acquire a lock on a non-relation database object.</entry>
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</row>
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<row>
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<entry><literal>userlock</></entry>
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<entry>Waiting to acquire a userlock.</entry>
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</row>
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<row>
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<entry><literal>advisory</></entry>
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<entry>Waiting to acquire an advisory user lock.</entry>
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</row>
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<row>
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<entry><literal>BufferPin</></entry>
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<entry><literal>BufferPin</></entry>
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<entry>Waiting to acquire a pin on a buffer.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<note>
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<para>
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For tranches registered by extensions, the name is specified by extension
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and this will be displayed as <structfield>wait_event</>. It is quite
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possible that user has registered the tranche in one of the backends (by
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having allocation in dynamic shared memory) in which case other backends
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won't have that information, so we display <literal>extension</> for such
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cases.
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</para>
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</note>
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<para>
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Here is an example of how wait events can be viewed
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<programlisting>
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SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event is NOT NULL;
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pid | wait_event_type | wait_event
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------+-----------------+---------------
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2540 | Lock | relation
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6644 | LWLockNamed | ProcArrayLock
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(2 rows)
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</programlisting>
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</para>
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<table id="pg-stat-replication-view" xreflabel="pg_stat_replication">
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<title><structname>pg_stat_replication</structname> View</title>
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<tgroup cols="3">
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@ -2030,10 +2412,20 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
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<entry>OID of the user logged into this backend</entry>
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</row>
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<row>
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<entry><literal><function>pg_stat_get_backend_wait_event_type(integer)</function></literal></entry>
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<entry><type>text</type></entry>
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<entry>Wait event type name if backend is currently waiting, otherwise NULL.
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See <xref linkend="wait-event-table"> for details.
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</entry>
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||||
</row>
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<row>
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<entry><literal><function>pg_stat_get_backend_waiting(integer)</function></literal></entry>
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<entry><type>boolean</type></entry>
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<entry>True if this backend is currently waiting on a lock</entry>
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<entry><literal><function>pg_stat_get_backend_wait_event(integer)</function></literal></entry>
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||||
<entry><type>text</type></entry>
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||||
<entry>Wait event name if backend is currently waiting, otherwise NULL.
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||||
See <xref linkend="wait-event-table"> for details.
|
||||
</entry>
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||||
</row>
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||||
|
||||
<row>
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||||
|
||||
Reference in New Issue
Block a user