From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Cc: Greg Nancarrow <gregn4422@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>
Cc: Smith, Peter <peters@fast.au.fujitsu.com>
Cc: David Steele <david@pgmasters.net>
Cc: Tsunakawa, Takayuki <tsunakawa.takay@fujitsu.com>
Cc: Haribabu Kommi <kommi.haribabu@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Dave Cramer <pg@fastcrypt.com>
Cc: Jing Wang <jingwangian@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Elvis Pranskevichus <elprans@gmail.com>
Subject: Re: Libpq support to connect to standby server as priority
Date: Tue, 24 Nov 2020 20:07:14 -0500
Message-ID: <388250.1606266434@sss.pgh.pa.us> (raw)
In-Reply-To: <325979.1606259987@sss.pgh.pa.us>
References: <20201124225917.GA21884@alvherre.pgsql>
<325979.1606259987@sss.pgh.pa.us>
I wrote:
> Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
>> Agreed. If this is just a few hundred bytes of server-side local memory
>> per backend, it seems definitely worth it.
> Yeah, given the current set of GUC_REPORT variables, it's hard to see
> the storage for their last-reported values amounting to much. The need
> for an extra pointer field in each GUC variable record might eat more
> space than the actually-live values :-(
Here's a v2 that does it like that.
regards, tom lane
Attachments:0001-report-guc-changes-at-query-end-2.patch (text/x-diff, 5.9K) downloaddiff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.cindex 7c5f7c775b..34ed0e7558 100644--- a/src/backend/tcop/postgres.c+++ b/src/backend/tcop/postgres.c@@ -4229,6 +4229,9 @@ PostgresMain(int argc, char *argv[],
pgstat_report_activity(STATE_IDLE, NULL);
}
+ /* Report any recently-changed GUC options */+ ReportChangedGUCOptions();+
ReadyForQuery(whereToSendOutput);
send_ready_for_query = false;
}
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.cindex bb34630e8e..245a3472bc 100644--- a/src/backend/utils/misc/guc.c+++ b/src/backend/utils/misc/guc.c@@ -4822,6 +4822,8 @@ static bool guc_dirty; /* true if need to do commit/abort work */
static bool reporting_enabled; /* true to enable GUC_REPORT */
+static bool report_needed; /* true if any GUC_REPORT reports are needed */+
static int GUCNestLevel = 0; /* 1 when in main transaction */
@@ -5452,6 +5454,7 @@ InitializeOneGUCOption(struct config_generic *gconf)
gconf->reset_scontext = PGC_INTERNAL;
gconf->stack = NULL;
gconf->extra = NULL;
+ gconf->last_reported = NULL;
gconf->sourcefile = NULL;
gconf->sourceline = 0;
@@ -5828,7 +5831,10 @@ ResetAllOptions(void)
gconf->scontext = gconf->reset_scontext;
if (gconf->flags & GUC_REPORT)
- ReportGUCOption(gconf);+ {+ gconf->status |= GUC_NEEDS_REPORT;+ report_needed = true;+ }
}
}
@@ -6215,7 +6221,10 @@ AtEOXact_GUC(bool isCommit, int nestLevel)
/* Report new value if we changed it */
if (changed && (gconf->flags & GUC_REPORT))
- ReportGUCOption(gconf);+ {+ gconf->status |= GUC_NEEDS_REPORT;+ report_needed = true;+ }
} /* end of stack-popping loop */
if (stack != NULL)
@@ -6257,17 +6266,60 @@ BeginReportingGUCOptions(void)
if (conf->flags & GUC_REPORT)
ReportGUCOption(conf);
}
++ report_needed = false;+}++/*+ * ReportChangedGUCOptions: report recently-changed GUC_REPORT variables+ *+ * This is called just before we wait for a new client query.+ *+ * By handling things this way, we ensure that a ParameterStatus message+ * is sent at most once per variable per query, even if the variable+ * changed multiple times within the query. That's quite possible when+ * using features such as function SET clauses. Function SET clauses+ * also tend to cause values to change intraquery but eventually revert+ * to their prevailing values; ReportGUCOption is responsible for avoiding+ * redundant reports in such cases.+ */+void+ReportChangedGUCOptions(void)+{+ /* Quick exit if not (yet) enabled */+ if (!reporting_enabled)+ return;++ /* Quick exit if no values have been changed */+ if (!report_needed)+ return;++ /* Transmit new values of interesting variables */+ for (int i = 0; i < num_guc_variables; i++)+ {+ struct config_generic *conf = guc_variables[i];++ if ((conf->flags & GUC_REPORT) && (conf->status & GUC_NEEDS_REPORT))+ ReportGUCOption(conf);+ }++ report_needed = false;
}
/*
* ReportGUCOption: if appropriate, transmit option value to frontend
+ *+ * We need not transmit the value if it's the same as what we last+ * transmitted. However, clear the NEEDS_REPORT flag in any case.
*/
static void
ReportGUCOption(struct config_generic *record)
{
- if (reporting_enabled && (record->flags & GUC_REPORT))+ char *val = _ShowOption(record, false);++ if (record->last_reported == NULL ||+ strcmp(val, record->last_reported) != 0)
{
- char *val = _ShowOption(record, false);
StringInfoData msgbuf;
pq_beginmessage(&msgbuf, 'S');
@@ -6275,8 +6327,19 @@ ReportGUCOption(struct config_generic *record)
pq_sendstring(&msgbuf, val);
pq_endmessage(&msgbuf);
- pfree(val);+ /*+ * We need a long-lifespan copy. If strdup() fails due to OOM, we'll+ * set last_reported to NULL and thereby possibly make a duplicate+ * report later.+ */+ if (record->last_reported)+ free(record->last_reported);+ record->last_reported = strdup(val);
}
++ pfree(val);++ record->status &= ~GUC_NEEDS_REPORT;
}
/*
@@ -7695,7 +7758,10 @@ set_config_option(const char *name, const char *value,
}
if (changeVal && (record->flags & GUC_REPORT))
- ReportGUCOption(record);+ {+ record->status |= GUC_NEEDS_REPORT;+ report_needed = true;+ }
return changeVal ? 1 : -1;
}
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.hindex 073c8f3e06..6a20a3bcec 100644--- a/src/include/utils/guc.h+++ b/src/include/utils/guc.h@@ -363,6 +363,7 @@ extern void AtStart_GUC(void);
extern int NewGUCNestLevel(void);
extern void AtEOXact_GUC(bool isCommit, int nestLevel);
extern void BeginReportingGUCOptions(void);
+extern void ReportChangedGUCOptions(void);
extern void ParseLongOption(const char *string, char **name, char **value);
extern bool parse_int(const char *value, int *result, int flags,
const char **hintmsg);
diff --git a/src/include/utils/guc_tables.h b/src/include/utils/guc_tables.hindex 04431d0eb2..7f36e1146f 100644--- a/src/include/utils/guc_tables.h+++ b/src/include/utils/guc_tables.h@@ -161,6 +161,8 @@ struct config_generic
GucContext reset_scontext; /* context that set the reset value */
GucStack *stack; /* stacked prior values */
void *extra; /* "extra" pointer for current actual value */
+ char *last_reported; /* if variable is GUC_REPORT, value last sent+ * to client (NULL if not yet sent) */
char *sourcefile; /* file current setting is from (NULL if not
* set in config file) */
int sourceline; /* line in source file */
@@ -172,7 +174,8 @@ struct config_generic
* Caution: the GUC_IS_IN_FILE bit is transient state for ProcessConfigFile.
* Do not assume that its value represents useful information elsewhere.
*/
-#define GUC_PENDING_RESTART 0x0002+#define GUC_PENDING_RESTART 0x0002 /* changed value cannot be applied yet */+#define GUC_NEEDS_REPORT 0x0004 /* new value must be reported to client */
/* GUC records for specific variable types */
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, alvherre@alvh.no-ip.org, a.lubennikova@postgrespro.ru, gregn4422@gmail.com, smithpb2250@gmail.com, peters@fast.au.fujitsu.com, david@pgmasters.net, tsunakawa.takay@fujitsu.com, kommi.haribabu@gmail.com, robertmhaas@gmail.com, laurenz.albe@cybertec.at, pg@fastcrypt.com, jingwangian@gmail.com, elprans@gmail.com
Subject: Re: Libpq support to connect to standby server as priority
In-Reply-To: <388250.1606266434@sss.pgh.pa.us>
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