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Commitff245a3

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Doc: improve descriptions of max_[pred_]locks_per_transaction GUCs.
The old wording described these as being multiplied by max_connectionsplus max_prepared_transactions, which hasn't been exactly right forsome time thanks to the addition of various auxiliary processes.Moreover, exactness here is a bit pointless given that the lock tablescan expand into the initially-unallocated "slop" space in sharedmemory. Rather than trying to track exactly what the code is doing,let's just use the term "server processes".Likewise adjust these GUCs' description strings in guc_tables.c.Wang Wei, reviewed by Nathan Bossart and myselfDiscussion:https://postgr.es/m/OS3PR01MB6275BDD09C9B875C65FCC5AB9EA39@OS3PR01MB6275.jpnprd01.prod.outlook.com
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‎doc/src/sgml/config.sgml‎

Lines changed: 13 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -10236,13 +10236,12 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
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</term>
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<listitem>
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<para>
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The shared lock table tracks locks on
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<varname>max_locks_per_transaction</varname> * (<xref
10241-
linkend="guc-max-connections"/> + <xref
10242-
linkend="guc-max-prepared-transactions"/>) objects (e.g., tables);
10239+
The shared lock table has space for
10240+
<varname>max_locks_per_transaction</varname> objects
10241+
(e.g., tables) per server process or prepared transaction;
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hence, no more than this many distinct objects can be locked at
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any one time. This parametercontrols the average number of object
10245-
locksallocated for each transaction; individual transactions
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any one time. This parameterlimits the average number of object
10244+
locksused by each transaction; individual transactions
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can lock more objects as long as the locks of all transactions
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fit in the lock table. This is <emphasis>not</emphasis> the number of
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rows that can be locked; that value is unlimited. The default,
@@ -10253,8 +10252,8 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
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</para>
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<para>
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When running a standby server, you must set this parameter to the
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same or higher valuethan on the primary server. Otherwise, queries
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When running a standby server, you must set this parameter tohavethe
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same or higher valueas on the primary server. Otherwise, queries
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will not be allowed in the standby server.
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</para>
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</listitem>
@@ -10268,17 +10267,16 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
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</term>
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<listitem>
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<para>
10271-
The shared predicate lock table tracks locks on
10272-
<varname>max_pred_locks_per_transaction</varname> * (<xref
10273-
linkend="guc-max-connections"/> + <xref
10274-
linkend="guc-max-prepared-transactions"/>) objects (e.g., tables);
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The shared predicate lock table has space for
10271+
<varname>max_pred_locks_per_transaction</varname> objects
10272+
(e.g., tables) per server process or prepared transaction;
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hence, no more than this many distinct objects can be locked at
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any one time. This parametercontrols the average number of object
10277-
locksallocated for each transaction; individual transactions
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any one time. This parameterlimits the average number of object
10275+
locksused by each transaction; individual transactions
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can lock more objects as long as the locks of all transactions
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fit in the lock table. This is <emphasis>not</emphasis> the number of
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rows that can be locked; that value is unlimited. The default,
10281-
64, hasgenerally been sufficient in testing, but you might need to
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64, hashistorically proven sufficient, but you might need to
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raise this value if you have clients that touch many different
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tables in a single serializable transaction. This parameter can
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only be set at server start.

‎src/backend/utils/misc/guc_tables.c‎

Lines changed: 5 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -2599,9 +2599,9 @@ struct config_int ConfigureNamesInt[] =
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{
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{"max_locks_per_transaction",PGC_POSTMASTER,LOCK_MANAGEMENT,
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gettext_noop("Sets the maximum number of locks per transaction."),
2602-
gettext_noop("The shared lock table is sized on the assumption that "
2603-
"at most max_locks_per_transaction * max_connections distinct "
2604-
"objects will need to be locked at any one time.")
2602+
gettext_noop("The shared lock table is sized on the assumption thatat most"
2603+
"max_locks_per_transaction objects per server process or prepared "
2604+
"transaction will need to be locked at any one time.")
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},
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&max_locks_per_xact,
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64,10,INT_MAX,
@@ -2612,8 +2612,8 @@ struct config_int ConfigureNamesInt[] =
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{"max_pred_locks_per_transaction",PGC_POSTMASTER,LOCK_MANAGEMENT,
26132613
gettext_noop("Sets the maximum number of predicate locks per transaction."),
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gettext_noop("The shared predicate lock table is sized on the assumption that "
2615-
"at most max_pred_locks_per_transaction* max_connections distinct "
2616-
"objects will need to be locked at any one time.")
2615+
"at most max_pred_locks_per_transactionobjects per server process "
2616+
"or prepared transaction will need to be locked at any one time.")
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},
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&max_predicate_locks_per_xact,
26192619
64,10,INT_MAX,

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