<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >System Administration Functions</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 8.4.12 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Functions and Operators" HREF="functions.html"><LINK REL="PREVIOUS" TITLE="System Information Functions" HREF="functions-info.html"><LINK REL="NEXT" TITLE="Trigger Functions" HREF="functions-trigger.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2012-05-31T23:30:11"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" >PostgreSQL 8.4.12 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="functions-info.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="functions.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 9. Functions and Operators</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="functions.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="functions-trigger.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="FUNCTIONS-ADMIN" >9.24. System Administration Functions</A ></H1 ><P > <A HREF="functions-admin.html#FUNCTIONS-ADMIN-SET-TABLE" >Table 9-54</A > shows the functions available to query and alter run-time configuration parameters. </P ><DIV CLASS="TABLE" ><A NAME="FUNCTIONS-ADMIN-SET-TABLE" ></A ><P ><B >Table 9-54. Configuration Settings Functions</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Return Type</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >current_setting</CODE >(<TT CLASS="PARAMETER" >setting_name</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >get current value of setting</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >set_config(<TT CLASS="PARAMETER" >setting_name</TT >, <TT CLASS="PARAMETER" >new_value</TT >, <TT CLASS="PARAMETER" >is_local</TT >)</CODE ></TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >set parameter and return new value</TD ></TR ></TBODY ></TABLE ></DIV ><A NAME="AEN17954" ></A ><A NAME="AEN17956" ></A ><A NAME="AEN17958" ></A ><P > The function <CODE CLASS="FUNCTION" >current_setting</CODE > yields the current value of the setting <TT CLASS="PARAMETER" >setting_name</TT >. It corresponds to the <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > command <TT CLASS="COMMAND" >SHOW</TT >. An example: </P><PRE CLASS="PROGRAMLISTING" >SELECT current_setting('datestyle'); current_setting ----------------- ISO, MDY (1 row)</PRE ><P> </P ><P > <CODE CLASS="FUNCTION" >set_config</CODE > sets the parameter <TT CLASS="PARAMETER" >setting_name</TT > to <TT CLASS="PARAMETER" >new_value</TT >. If <TT CLASS="PARAMETER" >is_local</TT > is <TT CLASS="LITERAL" >true</TT >, the new value will only apply to the current transaction. If you want the new value to apply for the current session, use <TT CLASS="LITERAL" >false</TT > instead. The function corresponds to the SQL command <TT CLASS="COMMAND" >SET</TT >. An example: </P><PRE CLASS="PROGRAMLISTING" >SELECT set_config('log_statement_stats', 'off', false); set_config ------------ off (1 row)</PRE ><P> </P ><A NAME="AEN17977" ></A ><A NAME="AEN17979" ></A ><A NAME="AEN17981" ></A ><A NAME="AEN17983" ></A ><A NAME="AEN17985" ></A ><P > The functions shown in <A HREF="functions-admin.html#FUNCTIONS-ADMIN-SIGNAL-TABLE" >Table 9-55</A > send control signals to other server processes. Use of these functions is restricted to superusers. </P ><DIV CLASS="TABLE" ><A NAME="FUNCTIONS-ADMIN-SIGNAL-TABLE" ></A ><P ><B >Table 9-55. Server Signalling Functions</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Return Type</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_cancel_backend</CODE >(<TT CLASS="PARAMETER" >pid</TT > <TT CLASS="TYPE" >int</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Cancel a backend's current query</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_terminate_backend</CODE >(<TT CLASS="PARAMETER" >pid</TT > <TT CLASS="TYPE" >int</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Terminate a backend</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_reload_conf</CODE >()</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Cause server processes to reload their configuration files</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_rotate_logfile</CODE >()</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Rotate server's log file</TD ></TR ></TBODY ></TABLE ></DIV ><P > Each of these functions returns <TT CLASS="LITERAL" >true</TT > if successful and <TT CLASS="LITERAL" >false</TT > otherwise. </P ><P > <CODE CLASS="FUNCTION" >pg_cancel_backend</CODE > and <CODE CLASS="FUNCTION" >pg_terminate_backend</CODE > send signals (<SPAN CLASS="SYSTEMITEM" >SIGINT</SPAN > or <SPAN CLASS="SYSTEMITEM" >SIGTERM</SPAN > respectively) to backend processes identified by process ID. The process ID of an active backend can be found from the <TT CLASS="STRUCTFIELD" >procpid</TT > column of the <TT CLASS="STRUCTNAME" >pg_stat_activity</TT > view, or by listing the <TT CLASS="COMMAND" >postgres</TT > processes on the server (using <SPAN CLASS="APPLICATION" >ps</SPAN > on Unix or the <SPAN CLASS="APPLICATION" >Task Manager</SPAN > on <SPAN CLASS="PRODUCTNAME" >Windows</SPAN >). </P ><P > <CODE CLASS="FUNCTION" >pg_reload_conf</CODE > sends a <SPAN CLASS="SYSTEMITEM" >SIGHUP</SPAN > signal to the server, causing configuration files to be reloaded by all server processes. </P ><P > <CODE CLASS="FUNCTION" >pg_rotate_logfile</CODE > signals the log-file manager to switch to a new output file immediately. This works only when the built-in log collector is running, since otherwise there is no log-file manager subprocess. </P ><A NAME="AEN18050" ></A ><A NAME="AEN18052" ></A ><A NAME="AEN18054" ></A ><A NAME="AEN18056" ></A ><A NAME="AEN18058" ></A ><A NAME="AEN18060" ></A ><A NAME="AEN18062" ></A ><A NAME="AEN18064" ></A ><P > The functions shown in <A HREF="functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE" >Table 9-56</A > assist in making on-line backups. Use of the first three functions is restricted to superusers. </P ><DIV CLASS="TABLE" ><A NAME="FUNCTIONS-ADMIN-BACKUP-TABLE" ></A ><P ><B >Table 9-56. Backup Control Functions</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Return Type</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_start_backup</CODE >(<TT CLASS="PARAMETER" >label</TT > <TT CLASS="TYPE" >text</TT > [<SPAN CLASS="OPTIONAL" >, <TT CLASS="PARAMETER" >fast</TT > <TT CLASS="TYPE" >boolean</TT > </SPAN >])</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >Prepare for performing on-line backup</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stop_backup</CODE >()</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >Finish performing on-line backup</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_switch_xlog</CODE >()</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >Force switch to a new transaction log file</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_current_xlog_location</CODE >()</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >Get current transaction log write location</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_current_xlog_insert_location</CODE >()</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >Get current transaction log insert location</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_xlogfile_name_offset</CODE >(<TT CLASS="PARAMETER" >location</TT > <TT CLASS="TYPE" >text</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT >, <TT CLASS="TYPE" >integer</TT ></TD ><TD >Convert transaction log location string to file name and decimal byte offset within file</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_xlogfile_name</CODE >(<TT CLASS="PARAMETER" >location</TT > <TT CLASS="TYPE" >text</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >Convert transaction log location string to file name</TD ></TR ></TBODY ></TABLE ></DIV ><P > <CODE CLASS="FUNCTION" >pg_start_backup</CODE > accepts an arbitrary user-defined label for the backup. (Typically this would be the name under which the backup dump file will be stored.) The function writes a backup label file (<TT CLASS="FILENAME" >backup_label</TT >) into the database cluster's data directory, performs a checkpoint, and then returns the backup's starting transaction log location as text. The user can ignore this result value, but it is provided in case it is useful. </P><PRE CLASS="PROGRAMLISTING" >postgres=# select pg_start_backup('label_goes_here'); pg_start_backup ----------------- 0/D4445B8 (1 row)</PRE ><P> There is an optional boolean second parameter. If <TT CLASS="LITERAL" >true</TT >, it specifies executing <CODE CLASS="FUNCTION" >pg_start_backup</CODE > as quickly as possible. This forces an immediate checkpoint which will cause a spike in I/O operations, slowing any concurrently executing queries. </P ><P > <CODE CLASS="FUNCTION" >pg_stop_backup</CODE > removes the label file created by <CODE CLASS="FUNCTION" >pg_start_backup</CODE >, and creates a backup history file in the transaction log archive area. The history file includes the label given to <CODE CLASS="FUNCTION" >pg_start_backup</CODE >, the starting and ending transaction log locations for the backup, and the starting and ending times of the backup. The return value is the backup's ending transaction log location (which again can be ignored). After recording the ending location, the current transaction log insertion point is automatically advanced to the next transaction log file, so that the ending transaction log file can be archived immediately to complete the backup. </P ><P > <CODE CLASS="FUNCTION" >pg_switch_xlog</CODE > moves to the next transaction log file, allowing the current file to be archived (assuming you are using continuous archiving). The return value is the ending transaction log location + 1 within the just-completed transaction log file. If there has been no transaction log activity since the last transaction log switch, <CODE CLASS="FUNCTION" >pg_switch_xlog</CODE > does nothing and returns the start location of the transaction log file currently in use. </P ><P > <CODE CLASS="FUNCTION" >pg_current_xlog_location</CODE > displays the current transaction log write location in the same format used by the above functions. Similarly, <CODE CLASS="FUNCTION" >pg_current_xlog_insert_location</CODE > displays the current transaction log insertion point. The insertion point is the <SPAN CLASS="QUOTE" >"logical"</SPAN > end of the transaction log at any instant, while the write location is the end of what has actually been written out from the server's internal buffers. The write location is the end of what can be examined from outside the server, and is usually what you want if you are interested in archiving partially-complete transaction log files. The insertion point is made available primarily for server debugging purposes. These are both read-only operations and do not require superuser permissions. </P ><P > You can use <CODE CLASS="FUNCTION" >pg_xlogfile_name_offset</CODE > to extract the corresponding transaction log file name and byte offset from the results of any of the above functions. For example: </P><PRE CLASS="PROGRAMLISTING" >postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup()); file_name | file_offset --------------------------+------------- 00000001000000000000000D | 4039624 (1 row)</PRE ><P> Similarly, <CODE CLASS="FUNCTION" >pg_xlogfile_name</CODE > extracts just the transaction log file name. When the given transaction log location is exactly at a transaction log file boundary, both these functions return the name of the preceding transaction log file. This is usually the desired behavior for managing transaction log archiving behavior, since the preceding file is the last one that currently needs to be archived. </P ><P > For details about proper usage of these functions, see <A HREF="continuous-archiving.html" >Section 24.3</A >. </P ><P > The functions shown in <A HREF="functions-admin.html#FUNCTIONS-ADMIN-DBSIZE" >Table 9-57</A > calculate the disk space usage of database objects. </P ><A NAME="AEN18161" ></A ><A NAME="AEN18163" ></A ><A NAME="AEN18165" ></A ><A NAME="AEN18167" ></A ><A NAME="AEN18169" ></A ><A NAME="AEN18171" ></A ><DIV CLASS="TABLE" ><A NAME="FUNCTIONS-ADMIN-DBSIZE" ></A ><P ><B >Table 9-57. Database Object Size Functions</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Return Type</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_column_size</CODE >(<TT CLASS="TYPE" >any</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >int</TT ></TD ><TD >Number of bytes used to store a particular value (possibly compressed)</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_database_size</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD >Disk space used by the database with the specified OID</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_database_size</CODE >(<TT CLASS="TYPE" >name</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD >Disk space used by the database with the specified name</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_relation_size</CODE >(<TT CLASS="PARAMETER" >relation</TT > <TT CLASS="TYPE" >regclass</TT >, <TT CLASS="PARAMETER" >fork</TT > <TT CLASS="TYPE" >text</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Disk space used by the specified fork (<TT CLASS="LITERAL" >'main'</TT >, <TT CLASS="LITERAL" >'fsm'</TT > or <TT CLASS="LITERAL" >'vm'</TT >) of the table or index with the specified OID or name </TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_relation_size</CODE >(<TT CLASS="PARAMETER" >relation</TT > <TT CLASS="TYPE" >regclass</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Shorthand for <TT CLASS="LITERAL" >pg_relation_size(..., 'main')</TT > </TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_size_pretty</CODE >(<TT CLASS="TYPE" >bigint</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >Converts a size in bytes into a human-readable format with size units</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_tablespace_size</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD >Disk space used by the tablespace with the specified OID</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_tablespace_size</CODE >(<TT CLASS="TYPE" >name</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD >Disk space used by the tablespace with the specified name</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_total_relation_size</CODE >(<TT CLASS="TYPE" >regclass</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Total disk space used by the table with the specified OID or name, including indexes and <ACRONYM CLASS="ACRONYM" >TOAST</ACRONYM > data </TD ></TR ></TBODY ></TABLE ></DIV ><P > <CODE CLASS="FUNCTION" >pg_column_size</CODE > shows the space used to store any individual data value. </P ><P > <CODE CLASS="FUNCTION" >pg_database_size</CODE > and <CODE CLASS="FUNCTION" >pg_tablespace_size</CODE > accept the OID or name of a database or tablespace, and return the total disk space used therein. </P ><P > <CODE CLASS="FUNCTION" >pg_relation_size</CODE > accepts the OID or name of a table, index or toast table, and returns the size in bytes. Specifying <TT CLASS="LITERAL" >'main'</TT > or leaving out the second argument returns the size of the main data fork of the relation. Specifying <TT CLASS="LITERAL" >'fsm'</TT > returns the size of the Free Space Map (see <A HREF="storage-fsm.html" >Section 53.3</A >) associated with the relation. Specifying <TT CLASS="LITERAL" >'vm'</TT > returns the size of the Visibility Map (see <A HREF="storage-vm.html" >Section 53.4</A >) associated with the relation. </P ><P > <CODE CLASS="FUNCTION" >pg_size_pretty</CODE > can be used to format the result of one of the other functions in a human-readable way, using kB, MB, GB or TB as appropriate. </P ><P > <CODE CLASS="FUNCTION" >pg_total_relation_size</CODE > accepts the OID or name of a table or toast table, and returns the size in bytes of the data and all associated indexes and toast tables. </P ><P > The functions shown in <A HREF="functions-admin.html#FUNCTIONS-ADMIN-GENFILE" >Table 9-58</A > provide native access to files on the machine hosting the server. Only files within the database cluster directory and the <TT CLASS="VARNAME" >log_directory</TT > can be accessed. Use a relative path for files in the cluster directory, and a path matching the <TT CLASS="VARNAME" >log_directory</TT > configuration setting for log files. Use of these functions is restricted to superusers. </P ><DIV CLASS="TABLE" ><A NAME="FUNCTIONS-ADMIN-GENFILE" ></A ><P ><B >Table 9-58. Generic File Access Functions</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Return Type</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_ls_dir</CODE >(<TT CLASS="PARAMETER" >dirname</TT > <TT CLASS="TYPE" >text</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >setof text</TT ></TD ><TD >List the contents of a directory</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_read_file</CODE >(<TT CLASS="PARAMETER" >filename</TT > <TT CLASS="TYPE" >text</TT >, <TT CLASS="PARAMETER" >offset</TT > <TT CLASS="TYPE" >bigint</TT >, <TT CLASS="PARAMETER" >length</TT > <TT CLASS="TYPE" >bigint</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD >Return the contents of a text file</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_file</CODE >(<TT CLASS="PARAMETER" >filename</TT > <TT CLASS="TYPE" >text</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >record</TT ></TD ><TD >Return information about a file</TD ></TR ></TBODY ></TABLE ></DIV ><A NAME="AEN18323" ></A ><P > <CODE CLASS="FUNCTION" >pg_ls_dir</CODE > returns all the names in the specified directory, except the special entries <SPAN CLASS="QUOTE" >"<TT CLASS="LITERAL" >.</TT >"</SPAN > and <SPAN CLASS="QUOTE" >"<TT CLASS="LITERAL" >..</TT >"</SPAN >. </P ><A NAME="AEN18331" ></A ><P > <CODE CLASS="FUNCTION" >pg_read_file</CODE > returns part of a text file, starting at the given <TT CLASS="PARAMETER" >offset</TT >, returning at most <TT CLASS="PARAMETER" >length</TT > bytes (less if the end of file is reached first). If <TT CLASS="PARAMETER" >offset</TT > is negative, it is relative to the end of the file. </P ><A NAME="AEN18338" ></A ><P > <CODE CLASS="FUNCTION" >pg_stat_file</CODE > returns a record containing the file size, last accessed time stamp, last modified time stamp, last file status change time stamp (Unix platforms only), file creation time stamp (Windows only), and a <TT CLASS="TYPE" >boolean</TT > indicating if it is a directory. Typical usages include: </P><PRE CLASS="PROGRAMLISTING" >SELECT * FROM pg_stat_file('filename'); SELECT (pg_stat_file('filename')).modification;</PRE ><P> </P ><P > The functions shown in <A HREF="functions-admin.html#FUNCTIONS-ADVISORY-LOCKS" >Table 9-59</A > manage advisory locks. For details about proper use of these functions, see <A HREF="explicit-locking.html#ADVISORY-LOCKS" >Section 13.3.4</A >. </P ><DIV CLASS="TABLE" ><A NAME="FUNCTIONS-ADVISORY-LOCKS" ></A ><P ><B >Table 9-59. Advisory Lock Functions</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Return Type</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_advisory_lock</CODE >(<TT CLASS="PARAMETER" >key</TT > <TT CLASS="TYPE" >bigint</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >void</TT ></TD ><TD >Obtain exclusive advisory lock</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_advisory_lock</CODE >(<TT CLASS="PARAMETER" >key1</TT > <TT CLASS="TYPE" >int</TT >, <TT CLASS="PARAMETER" >key2</TT > <TT CLASS="TYPE" >int</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >void</TT ></TD ><TD >Obtain exclusive advisory lock</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_advisory_lock_shared</CODE >(<TT CLASS="PARAMETER" >key</TT > <TT CLASS="TYPE" >bigint</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >void</TT ></TD ><TD >Obtain shared advisory lock</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_advisory_lock_shared</CODE >(<TT CLASS="PARAMETER" >key1</TT > <TT CLASS="TYPE" >int</TT >, <TT CLASS="PARAMETER" >key2</TT > <TT CLASS="TYPE" >int</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >void</TT ></TD ><TD >Obtain shared advisory lock</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_try_advisory_lock</CODE >(<TT CLASS="PARAMETER" >key</TT > <TT CLASS="TYPE" >bigint</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Obtain exclusive advisory lock if available</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_try_advisory_lock</CODE >(<TT CLASS="PARAMETER" >key1</TT > <TT CLASS="TYPE" >int</TT >, <TT CLASS="PARAMETER" >key2</TT > <TT CLASS="TYPE" >int</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Obtain exclusive advisory lock if available</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_try_advisory_lock_shared</CODE >(<TT CLASS="PARAMETER" >key</TT > <TT CLASS="TYPE" >bigint</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Obtain shared advisory lock if available</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_try_advisory_lock_shared</CODE >(<TT CLASS="PARAMETER" >key1</TT > <TT CLASS="TYPE" >int</TT >, <TT CLASS="PARAMETER" >key2</TT > <TT CLASS="TYPE" >int</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Obtain shared advisory lock if available</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_advisory_unlock</CODE >(<TT CLASS="PARAMETER" >key</TT > <TT CLASS="TYPE" >bigint</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Release an exclusive advisory lock</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_advisory_unlock</CODE >(<TT CLASS="PARAMETER" >key1</TT > <TT CLASS="TYPE" >int</TT >, <TT CLASS="PARAMETER" >key2</TT > <TT CLASS="TYPE" >int</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Release an exclusive advisory lock</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_advisory_unlock_shared</CODE >(<TT CLASS="PARAMETER" >key</TT > <TT CLASS="TYPE" >bigint</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Release a shared advisory lock</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_advisory_unlock_shared</CODE >(<TT CLASS="PARAMETER" >key1</TT > <TT CLASS="TYPE" >int</TT >, <TT CLASS="PARAMETER" >key2</TT > <TT CLASS="TYPE" >int</TT >)</TT > </TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD >Release a shared advisory lock</TD ></TR ><TR ><TD > <TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_advisory_unlock_all</CODE >()</TT > </TD ><TD ><TT CLASS="TYPE" >void</TT ></TD ><TD >Release all advisory locks held by the current session</TD ></TR ></TBODY ></TABLE ></DIV ><A NAME="AEN18483" ></A ><P > <CODE CLASS="FUNCTION" >pg_advisory_lock</CODE > locks an application-defined resource, which can be identified either by a single 64-bit key value or two 32-bit key values (note that these two key spaces do not overlap). The key type is specified in <TT CLASS="LITERAL" >pg_locks.objid</TT >. If another session already holds a lock on the same resource, the function will wait until the resource becomes available. The lock is exclusive. Multiple lock requests stack, so that if the same resource is locked three times it must be also unlocked three times to be released for other sessions' use. </P ><A NAME="AEN18488" ></A ><P > <CODE CLASS="FUNCTION" >pg_advisory_lock_shared</CODE > works the same as <CODE CLASS="FUNCTION" >pg_advisory_lock</CODE >, except the lock can be shared with other sessions requesting shared locks. Only would-be exclusive lockers are locked out. </P ><A NAME="AEN18493" ></A ><P > <CODE CLASS="FUNCTION" >pg_try_advisory_lock</CODE > is similar to <CODE CLASS="FUNCTION" >pg_advisory_lock</CODE >, except the function will not wait for the lock to become available. It will either obtain the lock immediately and return <TT CLASS="LITERAL" >true</TT >, or return <TT CLASS="LITERAL" >false</TT > if the lock cannot be acquired immediately. </P ><A NAME="AEN18500" ></A ><P > <CODE CLASS="FUNCTION" >pg_try_advisory_lock_shared</CODE > works the same as <CODE CLASS="FUNCTION" >pg_try_advisory_lock</CODE >, except it attempts to acquire a shared rather than an exclusive lock. </P ><A NAME="AEN18505" ></A ><P > <CODE CLASS="FUNCTION" >pg_advisory_unlock</CODE > will release a previously-acquired exclusive advisory lock. It returns <TT CLASS="LITERAL" >true</TT > if the lock is successfully released. If the lock was not held, it will return <TT CLASS="LITERAL" >false</TT >, and in addition, an SQL warning will be raised by the server. </P ><A NAME="AEN18511" ></A ><P > <CODE CLASS="FUNCTION" >pg_advisory_unlock_shared</CODE > works the same as <CODE CLASS="FUNCTION" >pg_advisory_unlock</CODE >, except it releases a shared advisory lock. </P ><A NAME="AEN18516" ></A ><P > <CODE CLASS="FUNCTION" >pg_advisory_unlock_all</CODE > will release all advisory locks held by the current session. (This function is implicitly invoked at session end, even if the client disconnects ungracefully.) </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="functions-info.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="functions-trigger.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >System Information Functions</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="functions.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Trigger Functions</TD ></TR ></TABLE ></DIV ></BODY ></HTML >