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><A
NAME="RUNTIME-CONFIG-LOCKS"
>18.12. 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 expensive, 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 checking 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. Only superusers can change
this setting.
</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 tracks 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
><P
> When running a standby server, you must set this parameter to the
same or higher value than on the master server. Otherwise, queries
will not be allowed in the standby server.
</P
></DD
><DT
><A
NAME="GUC-MAX-PRED-LOCKS-PER-TRANSACTION"
></A
><TT
CLASS="VARNAME"
>max_pred_locks_per_transaction</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
> The shared predicate lock table tracks locks on
<TT
CLASS="VARNAME"
>max_pred_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 generally been sufficient in testing, but you might need to
raise this value if you have clients that touch many different
tables in a single serializable 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
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