<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Lock Management</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="Server Configuration" HREF="runtime-config.html"><LINK REL="PREVIOUS" TITLE="Client Connection Defaults" HREF="runtime-config-client.html"><LINK REL="NEXT" TITLE="Version and Platform Compatibility" HREF="runtime-config-compatible.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="runtime-config-client.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="runtime-config.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 18. Server Configuration</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="runtime-config.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="runtime-config-compatible.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="RUNTIME-CONFIG-LOCKS" >18.11. Lock Management</A ></H1 ><P ></P ><DIV CLASS="VARIABLELIST" ><DL ><DT ><A NAME="GUC-DEADLOCK-TIMEOUT" ></A ><TT CLASS="VARNAME" >deadlock_timeout</TT > (<TT CLASS="TYPE" >integer</TT >)</DT ><DD ><P > This is the amount of time, in milliseconds, to wait on a lock before checking to see if there is a deadlock condition. The check for deadlock is relatively slow, so the server doesn't run it every time it waits for a lock. We optimistically assume that deadlocks are not common in production applications and just wait on the lock for a while before starting the check for a deadlock. Increasing this value reduces the amount of time wasted in needless deadlock checks, but slows down reporting of real deadlock errors. The default is one second (<TT CLASS="LITERAL" >1s</TT >), which is probably about the smallest value you would want in practice. On a heavily loaded server you might want to raise it. Ideally the setting should exceed your typical transaction time, so as to improve the odds that a lock will be released before the waiter decides to check for deadlock. </P ><P > When <A HREF="runtime-config-logging.html#GUC-LOG-LOCK-WAITS" >log_lock_waits</A > is set, this parameter also determines the length of time to wait before a log message is issued about the lock wait. If you are trying to investigate locking delays you might want to set a shorter than normal <TT CLASS="VARNAME" >deadlock_timeout</TT >. </P ></DD ><DT ><A NAME="GUC-MAX-LOCKS-PER-TRANSACTION" ></A ><TT CLASS="VARNAME" >max_locks_per_transaction</TT > (<TT CLASS="TYPE" >integer</TT >)</DT ><DD ><P > The shared lock table is created to track locks on <TT CLASS="VARNAME" >max_locks_per_transaction</TT > * (<A HREF="runtime-config-connection.html#GUC-MAX-CONNECTIONS" >max_connections</A > + <A HREF="runtime-config-resource.html#GUC-MAX-PREPARED-TRANSACTIONS" >max_prepared_transactions</A >) objects (e.g., tables); hence, no more than this many distinct objects can be locked at any one time. This parameter controls the average number of object locks allocated for each transaction; individual transactions can lock more objects as long as the locks of all transactions fit in the lock table. This is <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >not</I ></SPAN > the number of rows that can be locked; that value is unlimited. The default, 64, has historically proven sufficient, but you might need to raise this value if you have clients that touch many different tables in a single transaction. This parameter can only be set at server start. </P ><P > Increasing this parameter might cause <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > to request more <SPAN CLASS="SYSTEMITEM" >System V</SPAN > shared memory than your operating system's default configuration allows. See <A HREF="kernel-resources.html#SYSVIPC" >Section 17.4.1</A > for information on how to adjust those parameters, if necessary. </P ></DD ></DL ></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="runtime-config-client.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="runtime-config-compatible.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Client Connection Defaults</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="runtime-config.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Version and Platform Compatibility</TD ></TR ></TABLE ></DIV ></BODY ></HTML >