- new GUC in "Statement Behaviour" section, notify_duplicate_removal
(default true)
Initial discussion in this thread:
http://www.postgresql.org/message-id/CAP_rwwmpzk9=sbjrztod05bdctyc43wnknu_m37dygvl4sa...@mail.gmail.com
Rationale: for some legitimate use cases, duplicate removal is not
required, and it gets O(N^2) cost on large COPY/ insert transactions.
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 392eb70..9fb5504 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -6095,6 +6095,24 @@ SET XML OPTION { DOCUMENT | CONTENT };
</listitem>
</varlistentry>
+ <varlistentry id="guc-notify-duplicate-removal" xreflabel="notify_duplicate_removal">
+ <term><varname>notify_duplicate_removal</varname> (<type>bool</type>)
+ <indexterm>
+ <primary><varname>notify_duplicate_removal</> configuration parameter</primary>
+ </indexterm>
+ </term>
+ <listitem>
+ <para>
+ Try to remove duplicate messages while processing NOTIFY. When
+ <literal>on</> (the default), the server will avoid duplicate messages
+ (with same channel and payload). Setting this variable to
+ <literal>off</> can increase performance in some situations - at the
+ cost of having duplicate messages in NOTIFY queue. See <xref
+ linkend="SQL-NOTIFY"> for more information.
+ </para>
+ </listitem>
+ </varlistentry>
+
</variablelist>
</sect2>
<sect2 id="runtime-config-client-format">
diff --git a/doc/src/sgml/ref/notify.sgml b/doc/src/sgml/ref/notify.sgml
index 4dd5608..86a9bed 100644
--- a/doc/src/sgml/ref/notify.sgml
+++ b/doc/src/sgml/ref/notify.sgml
@@ -95,16 +95,17 @@ NOTIFY <replaceable class="PARAMETER">channel</replaceable> [ , <replaceable cla
<para>
If the same channel name is signaled multiple times from the same
- transaction with identical payload strings, the
- database server can decide to deliver a single notification only.
- On the other hand, notifications with distinct payload strings will
- always be delivered as distinct notifications. Similarly, notifications from
- different transactions will never get folded into one notification.
- Except for dropping later instances of duplicate notifications,
+ transaction with identical payload strings, and
+ <varname>notify_duplicate_removal</> is set to true, the database server
+ can decide to deliver a single notification only. On the other hand,
+ notifications with distinct payload strings will always be delivered as
+ distinct notifications. Similarly, notifications from different
+ transactions will never get folded into one notification. Except for
+ dropping later instances of duplicate notifications,
<command>NOTIFY</command> guarantees that notifications from the same
transaction get delivered in the order they were sent. It is also
- guaranteed that messages from different transactions are delivered in
- the order in which the transactions committed.
+ guaranteed that messages from different transactions are delivered in the
+ order in which the transactions committed.
</para>
<para>
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index c39ac3a..a7bc9f1 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -364,8 +364,9 @@ static bool amRegisteredListener = false;
/* has this backend sent notifications in the current transaction? */
static bool backendHasSentNotifications = false;
-/* GUC parameter */
+/* GUC parameters */
bool Trace_notify = false;
+bool notify_duplicate_removal = true;
/* local function prototypes */
static bool asyncQueuePagePrecedes(int p, int q);
@@ -570,9 +571,12 @@ Async_Notify(const char *channel, const char *payload)
errmsg("payload string too long")));
}
- /* no point in making duplicate entries in the list ... */
- if (AsyncExistsPendingNotify(channel, payload))
- return;
+ if (notify_duplicate_removal)
+ {
+ /* check for duplicate entries in the list */
+ if (AsyncExistsPendingNotify(channel, payload))
+ return;
+ }
/*
* The notification list needs to live until end of transaction, so store
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 83b8388..b737c29 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1617,6 +1617,15 @@ static struct config_bool ConfigureNamesBool[] =
false,
NULL, NULL, NULL
},
+ {
+ {"notify_duplicate_removal", PGC_USERSET, CLIENT_CONN_STATEMENT,
+ gettext_noop("Remove duplicate messages during NOTIFY."),
+ NULL
+ },
+ ¬ify_duplicate_removal,
+ true,
+ NULL, NULL, NULL
+ },
/* End-of-list marker */
{
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 029114f..2831c1b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -536,6 +536,7 @@
#xmloption = 'content'
#gin_fuzzy_search_limit = 0
#gin_pending_list_limit = 4MB
+#notify_duplicate_removal = on
# - Locale and Formatting -
diff --git a/src/include/commands/async.h b/src/include/commands/async.h
index b4c13fa..c572691 100644
--- a/src/include/commands/async.h
+++ b/src/include/commands/async.h
@@ -23,6 +23,7 @@
#define NUM_ASYNC_BUFFERS 8
extern bool Trace_notify;
+extern bool notify_duplicate_removal;
extern volatile sig_atomic_t notifyInterruptPending;
extern Size AsyncShmemSize(void);
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