<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >The Statistics Collector</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 8.3.1 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Monitoring Database Activity" HREF="monitoring.html"><LINK REL="PREVIOUS" TITLE="Standard Unix Tools" HREF="monitoring-ps.html"><LINK REL="NEXT" TITLE="Viewing Locks" HREF="monitoring-locks.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="2008-03-15T03:19:10"></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 8.3.1 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="monitoring-ps.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="monitoring.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 26. Monitoring Database Activity</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="monitoring.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="monitoring-locks.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="MONITORING-STATS" >26.2. The Statistics Collector</A ></H1 ><A NAME="AEN29117" ></A ><P > <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN >'s <I CLASS="FIRSTTERM" >statistics collector</I > is a subsystem that supports collection and reporting of information about server activity. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. It also tracks total numbers of rows in each table, and the last vacuum and analyze times for each table. </P ><P > <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > also supports determining the exact command currently being executed by other server processes. This is an independent facility that does not depend on the collector process. </P ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="MONITORING-STATS-SETUP" >26.2.1. Statistics Collection Configuration</A ></H2 ><P > Since collection of statistics adds some overhead to query execution, the system can be configured to collect or not collect information. This is controlled by configuration parameters that are normally set in <TT CLASS="FILENAME" >postgresql.conf</TT >. (See <A HREF="runtime-config.html" >Chapter 18</A > for details about setting configuration parameters.) </P ><P > The parameter <A HREF="runtime-config-statistics.html#GUC-TRACK-COUNTS" >track_counts</A > controls whether information is actually sent to the collector process and thus determines whether any run-time overhead occurs for event counting. </P ><P > The parameter <A HREF="runtime-config-statistics.html#GUC-TRACK-ACTIVITIES" >track_activities</A > enables monitoring of the current command being executed by any server process. </P ><P > Normally these parameters are set in <TT CLASS="FILENAME" >postgresql.conf</TT > so that they apply to all server processes, but it is possible to turn them on or off in individual sessions using the <A HREF="sql-set.html" ><I >SET</I ></A > command. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with <TT CLASS="COMMAND" >SET</TT >.) </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="MONITORING-STATS-VIEWS" >26.2.2. Viewing Collected Statistics</A ></H2 ><P > Several predefined views, listed in <A HREF="monitoring-stats.html#MONITORING-STATS-VIEWS-TABLE" >Table 26-1</A >, are available to show the results of statistics collection. Alternatively, one can build custom views using the underlying statistics functions. </P ><P > When using the statistics to monitor current activity, it is important to realize that the information does not update instantaneously. Each individual server process transmits new statistical counts to the collector just before going idle; so a query or transaction still in progress does not affect the displayed totals. Also, the collector itself emits a new report at most once per <TT CLASS="VARNAME" >PGSTAT_STAT_INTERVAL</TT > milliseconds (500 unless altered while building the server). So the displayed information lags behind actual activity. However, current-query information collected by <TT CLASS="VARNAME" >track_activities</TT > is always up-to-date. </P ><P > Another important point is that when a server process is asked to display any of these statistics, it first fetches the most recent report emitted by the collector process and then continues to use this snapshot for all statistical views and functions until the end of its current transaction. So the statistics will appear not to change as long as you continue the current transaction. Similarly, information about the current queries of all processes is collected when any such information is first requested within a transaction, and the same information will be displayed throughout the transaction. This is a feature, not a bug, because it allows you to perform several queries on the statistics and correlate the results without worrying that the numbers are changing underneath you. But if you want to see new results with each query, be sure to do the queries outside any transaction block. Alternatively, you can invoke <CODE CLASS="FUNCTION" >pg_stat_clear_snapshot</CODE >(), which will discard the current transaction's statistics snapshot (if any). The next use of statistical information will cause a new snapshot to be fetched. </P ><DIV CLASS="TABLE" ><A NAME="MONITORING-STATS-VIEWS-TABLE" ></A ><P ><B >Table 26-1. Standard Statistics Views</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><THEAD ><TR ><TH >View Name</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_stat_activity</TT ></TD ><TD >One row per server process, showing database OID, database name, process <ACRONYM CLASS="ACRONYM" >ID</ACRONYM >, user OID, user name, current query, query's waiting status, time at which the current transaction and current query began execution, time at which the process was started, and client's address and port number. The columns that report data on the current query are available unless the parameter <TT CLASS="VARNAME" >track_activities</TT > has been turned off. Furthermore, these columns are only visible if the user examining the view is a superuser or the same as the user owning the process being reported on. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_stat_bgwriter</TT ></TD ><TD >One row only, showing cluster-wide statistics from the background writer: number of scheduled checkpoints, requested checkpoints, buffers written by checkpoints and cleaning scans, and the number of times the background writer stopped a cleaning scan because it had written too many buffers. Also includes statistics about the shared buffer pool, including buffers written by backends (that is, not by the background writer) and total buffers allocated. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_stat_database</TT ></TD ><TD >One row per database, showing database OID, database name, number of active server processes connected to that database, number of transactions committed and rolled back in that database, total disk blocks read, total buffer hits (i.e., block read requests avoided by finding the block already in buffer cache), number of rows returned, inserted, updated and deleted. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_stat_all_tables</TT ></TD ><TD >For each table in the current database (including TOAST tables), the table OID, schema and table name, number of sequential scans initiated, number of live rows fetched by sequential scans, number of index scans initiated (over all indexes belonging to the table), number of live rows fetched by index scans, numbers of row insertions, updates, and deletions, number of row updates that were HOT (i.e., no separate index update), numbers of live and dead rows, the last time the table was vacuumed manually, the last time it was vacuumed by the autovacuum daemon, the last time it was analyzed manually, and the last time it was analyzed by the autovacuum daemon. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_stat_sys_tables</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_stat_all_tables</TT >, except that only system tables are shown.</TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_stat_user_tables</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_stat_all_tables</TT >, except that only user tables are shown.</TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_stat_all_indexes</TT ></TD ><TD >For each index in the current database, the table and index OID, schema, table and index name, number of index scans initiated on that index, number of index entries returned by index scans, and number of live table rows fetched by simple index scans using that index. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_stat_sys_indexes</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_stat_all_indexes</TT >, except that only indexes on system tables are shown.</TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_stat_user_indexes</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_stat_all_indexes</TT >, except that only indexes on user tables are shown.</TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_statio_all_tables</TT ></TD ><TD >For each table in the current database (including TOAST tables), the table OID, schema and table name, number of disk blocks read from that table, number of buffer hits, numbers of disk blocks read and buffer hits in all indexes of that table, numbers of disk blocks read and buffer hits from that table's auxiliary TOAST table (if any), and numbers of disk blocks read and buffer hits for the TOAST table's index. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_statio_sys_tables</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_statio_all_tables</TT >, except that only system tables are shown.</TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_statio_user_tables</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_statio_all_tables</TT >, except that only user tables are shown.</TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_statio_all_indexes</TT ></TD ><TD >For each index in the current database, the table and index OID, schema, table and index name, numbers of disk blocks read and buffer hits in that index. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_statio_sys_indexes</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_statio_all_indexes</TT >, except that only indexes on system tables are shown.</TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_statio_user_indexes</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_statio_all_indexes</TT >, except that only indexes on user tables are shown.</TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_statio_all_sequences</TT ></TD ><TD >For each sequence object in the current database, the sequence OID, schema and sequence name, numbers of disk blocks read and buffer hits in that sequence. </TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_statio_sys_sequences</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_statio_all_sequences</TT >, except that only system sequences are shown. (Presently, no system sequences are defined, so this view is always empty.)</TD ></TR ><TR ><TD ><TT CLASS="STRUCTNAME" >pg_statio_user_sequences</TT ></TD ><TD >Same as <TT CLASS="STRUCTNAME" >pg_statio_all_sequences</TT >, except that only user sequences are shown.</TD ></TR ></TBODY ></TABLE ></DIV ><P > The per-index statistics are particularly useful to determine which indexes are being used and how effective they are. </P ><P > Beginning in <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > 8.1, indexes can be used either directly or via <SPAN CLASS="QUOTE" >"bitmap scans"</SPAN >. In a bitmap scan the output of several indexes can be combined via AND or OR rules; so it is difficult to associate individual heap row fetches with specific indexes when a bitmap scan is used. Therefore, a bitmap scan increments the <TT CLASS="STRUCTNAME" >pg_stat_all_indexes</TT >.<TT CLASS="STRUCTFIELD" >idx_tup_read</TT > count(s) for the index(es) it uses, and it increments the <TT CLASS="STRUCTNAME" >pg_stat_all_tables</TT >.<TT CLASS="STRUCTFIELD" >idx_tup_fetch</TT > count for the table, but it does not affect <TT CLASS="STRUCTNAME" >pg_stat_all_indexes</TT >.<TT CLASS="STRUCTFIELD" >idx_tup_fetch</TT >. </P ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > Before <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > 8.1, the <TT CLASS="STRUCTFIELD" >idx_tup_read</TT > and <TT CLASS="STRUCTFIELD" >idx_tup_fetch</TT > counts were essentially always equal. Now they can be different even without considering bitmap scans, because <TT CLASS="STRUCTFIELD" >idx_tup_read</TT > counts index entries retrieved from the index while <TT CLASS="STRUCTFIELD" >idx_tup_fetch</TT > counts live rows fetched from the table; the latter will be less if any dead or not-yet-committed rows are fetched using the index. </P ></BLOCKQUOTE ></DIV ><P > The <TT CLASS="STRUCTNAME" >pg_statio_</TT > views are primarily useful to determine the effectiveness of the buffer cache. When the number of actual disk reads is much smaller than the number of buffer hits, then the cache is satisfying most read requests without invoking a kernel call. However, these statistics do not give the entire story: due to the way in which <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > handles disk I/O, data that is not in the <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > buffer cache might still reside in the kernel's I/O cache, and might therefore still be fetched without requiring a physical read. Users interested in obtaining more detailed information on <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > I/O behavior are advised to use the <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > statistics collector in combination with operating system utilities that allow insight into the kernel's handling of I/O. </P ><P > Other ways of looking at the statistics can be set up by writing queries that use the same underlying statistics access functions as these standard views do. These functions are listed in <A HREF="monitoring-stats.html#MONITORING-STATS-FUNCS-TABLE" >Table 26-2</A >. The per-database access functions take a database OID as argument to identify which database to report on. The per-table and per-index functions take a table or index OID. (Note that only tables and indexes in the current database can be seen with these functions.) The per-server-process access functions take a server process number, which ranges from one to the number of currently active server processes. </P ><DIV CLASS="TABLE" ><A NAME="MONITORING-STATS-FUNCS-TABLE" ></A ><P ><B >Table 26-2. Statistics Access Functions</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><THEAD ><TR ><TH >Function</TH ><TH >Return Type</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_numbackends</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >integer</TT ></TD ><TD > Number of active server processes for database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_xact_commit</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Transactions committed in database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_xact_rollback</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Transactions rolled back in database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_blocks_fetched</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of disk block fetch requests for database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_blocks_hit</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of disk block fetch requests found in cache for database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_tuples_returned</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of tuples returned for database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_tuples_fetched</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of tuples fetched for database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_tuples_inserted</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of tuples inserted in database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_tuples_updated</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of tuples updated in database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_db_tuples_deleted</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of tuples deleted in database </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_numscans</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of sequential scans done when argument is a table, or number of index scans done when argument is an index </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_tuples_returned</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of rows read by sequential scans when argument is a table, or number of index entries returned when argument is an index </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_tuples_fetched</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of table rows fetched by bitmap scans when argument is a table, or table rows fetched by simple index scans using the index when argument is an index </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_tuples_inserted</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of rows inserted into table </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_tuples_updated</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of rows updated in table (includes HOT updates) </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_tuples_deleted</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of rows deleted from table </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_tuples_hot_updated</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of rows HOT-updated in table </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_live_tuples</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of live rows in table </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_dead_tuples</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of dead rows in table </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_blocks_fetched</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of disk block fetch requests for table or index </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_blocks_hit</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > Number of disk block requests found in cache for table or index </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_last_vacuum_time</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >timestamptz</TT ></TD ><TD > Time of the last vacuum initiated by the user on this table </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_last_autovacuum_time</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >timestamptz</TT ></TD ><TD > Time of the last vacuum initiated by the autovacuum daemon on this table </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_last_analyze_time</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >timestamptz</TT ></TD ><TD > Time of the last analyze initiated by the user on this table </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_last_autoanalyze_time</CODE >(<TT CLASS="TYPE" >oid</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >timestamptz</TT ></TD ><TD > Time of the last analyze initiated by the autovacuum daemon on this table </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_idset</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >setof integer</TT ></TD ><TD > Set of currently active server process numbers (from 1 to the number of active server processes). See usage example in the text </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_backend_pid</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >integer</TT ></TD ><TD > Process ID of the server process attached to the current session </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_pid</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >integer</TT ></TD ><TD > Process ID of the given server process </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_dbid</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >oid</TT ></TD ><TD > Database ID of the given server process </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_userid</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >oid</TT ></TD ><TD > User ID of the given server process </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_activity</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD > Active command of the given server process, but only if the current user is a superuser or the same user as that of the session being queried (and <TT CLASS="VARNAME" >track_activities</TT > is on) </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_waiting</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >boolean</TT ></TD ><TD > True if the given server process is waiting for a lock, but only if the current user is a superuser or the same user as that of the session being queried (and <TT CLASS="VARNAME" >track_activities</TT > is on) </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_activity_start</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >timestamp with time zone</TT ></TD ><TD > The time at which the given server process' currently executing query was started, but only if the current user is a superuser or the same user as that of the session being queried (and <TT CLASS="VARNAME" >track_activities</TT > is on) </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_xact_start</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >timestamp with time zone</TT ></TD ><TD > The time at which the given server process' currently executing transaction was started, but only if the current user is a superuser or the same user as that of the session being queried (and <TT CLASS="VARNAME" >track_activities</TT > is on) </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_start</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >timestamp with time zone</TT ></TD ><TD > The time at which the given server process was started, or null if the current user is not a superuser nor the same user as that of the session being queried </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_client_addr</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >inet</TT ></TD ><TD > The IP address of the client connected to the given server process. Null if the connection is over a Unix domain socket. Also null if the current user is not a superuser nor the same user as that of the session being queried </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_backend_client_port</CODE >(<TT CLASS="TYPE" >integer</TT >)</TT ></TD ><TD ><TT CLASS="TYPE" >integer</TT ></TD ><TD > The IP port number of the client connected to the given server process. -1 if the connection is over a Unix domain socket. Null if the current user is not a superuser nor the same user as that of the session being queried </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_bgwriter_timed_checkpoints</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > The number of times the background writer has started timed checkpoints (because the <TT CLASS="VARNAME" >checkpoint_timeout</TT > time has expired) </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_bgwriter_requested_checkpoints</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > The number of times the background writer has started checkpoints based on requests from backends because the <TT CLASS="VARNAME" >checkpoint_segments</TT > has been exceeded or because the <TT CLASS="COMMAND" >CHECKPOINT</TT > command has been issued </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_bgwriter_buf_written_checkpoints</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > The number of buffers written by the background writer during checkpoints </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_bgwriter_buf_written_clean</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > The number of buffers written by the background writer for routine cleaning of dirty pages </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_bgwriter_maxwritten_clean</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > The number of times the background writer has stopped its cleaning scan because it has written more buffers than specified in the <TT CLASS="VARNAME" >bgwriter_lru_maxpages</TT > parameter </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_buf_written_backend</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > The number of buffers written by backends because they needed to allocate a new buffer </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_get_buf_alloc</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >bigint</TT ></TD ><TD > The total number of buffer allocations </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_clear_snapshot</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >void</TT ></TD ><TD > Discard the current statistics snapshot </TD ></TR ><TR ><TD ><TT CLASS="LITERAL" ><CODE CLASS="FUNCTION" >pg_stat_reset</CODE >()</TT ></TD ><TD ><TT CLASS="TYPE" >void</TT ></TD ><TD > Reset all statistics counters for the current database to zero (requires superuser privileges) </TD ></TR ></TBODY ></TABLE ></DIV ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > <CODE CLASS="FUNCTION" >blocks_fetched</CODE > minus <CODE CLASS="FUNCTION" >blocks_hit</CODE > gives the number of kernel <CODE CLASS="FUNCTION" >read()</CODE > calls issued for the table, index, or database; but the actual number of physical reads is usually lower due to kernel-level buffering. </P ></BLOCKQUOTE ></DIV ><P > The function <CODE CLASS="FUNCTION" >pg_stat_get_backend_idset</CODE > provides a convenient way to generate one row for each active server process. For example, to show the <ACRONYM CLASS="ACRONYM" >PID</ACRONYM >s and current queries of all server processes: </P><PRE CLASS="PROGRAMLISTING" >SELECT pg_stat_get_backend_pid(s.backendid) AS procpid, pg_stat_get_backend_activity(s.backendid) AS current_query FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS s;</PRE ><P> </P ></DIV ></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="monitoring-ps.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="monitoring-locks.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Standard Unix Tools</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="monitoring.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Viewing Locks</TD ></TR ></TABLE ></DIV ></BODY ></HTML >