Convert [autovacuum_]vacuum_cost_delay into floating-point GUCs.

This change makes it possible to specify sub-millisecond delays,
which work well on most modern platforms, though that was not true
when the cost-delay feature was designed.

To support this without breaking existing configuration entries,
improve guc.c to allow floating-point GUCs to have units.  Also,
allow "us" (microseconds) as an input/output unit for time-unit GUCs.
(It's not allowed as a base unit, at least not yet.)

Likewise change the autovacuum_vacuum_cost_delay reloption to be
floating-point; this forces a catversion bump because the layout of
StdRdOptions changes.

This patch doesn't in itself change the default values or allowed
ranges for these parameters, and it should not affect the behavior
for any already-allowed setting for them.

Discussion: https://postgr.es/m/1798.1552165479@sss.pgh.pa.us

Author: tglsfdc

doc/src/sgml/config.sgml

@@ -91,7 +91,9 @@
 
         <listitem>
          <para>
-          Valid time units are <literal>ms</literal> (milliseconds),
+          Valid time units are
+          <literal>us</literal> (microseconds),
+          <literal>ms</literal> (milliseconds),
           <literal>s</literal> (seconds), <literal>min</literal> (minutes),
           <literal>h</literal> (hours), and <literal>d</literal> (days).
          </para>
@@ -1845,7 +1847,7 @@ include_dir 'conf.d'
 
      <variablelist>
       <varlistentry id="guc-vacuum-cost-delay" xreflabel="vacuum_cost_delay">
-       <term><varname>vacuum_cost_delay</varname> (<type>integer</type>)
+       <term><varname>vacuum_cost_delay</varname> (<type>floating point</type>)
        <indexterm>
         <primary><varname>vacuum_cost_delay</varname> configuration parameter</primary>
        </indexterm>
@@ -1856,18 +1858,19 @@ include_dir 'conf.d'
          when the cost limit has been exceeded.
          The default value is zero, which disables the cost-based vacuum
          delay feature.  Positive values enable cost-based vacuuming.
-         Note that on many systems, the effective resolution
-         of sleep delays is 10 milliseconds; setting
-         <varname>vacuum_cost_delay</varname> to a value that is
-         not a multiple of 10 might have the same results as setting it
-         to the next higher multiple of 10.
         </para>
 
         <para>
          When using cost-based vacuuming, appropriate values for
          <varname>vacuum_cost_delay</varname> are usually quite small, perhaps
-         10 or 20 milliseconds.  Adjusting vacuum's resource consumption
-         is best done by changing the other vacuum cost parameters.
+         less than 1 millisecond.  While <varname>vacuum_cost_delay</varname>
+         can be set to fractional-millisecond values, such delays may not be
+         measured accurately on older platforms.  On such platforms,
+         increasing <command>VACUUM</command>'s throttled resource consumption
+         above what you get at 1ms will require changing the other vacuum cost
+         parameters.  You should, nonetheless,
+         keep <varname>vacuum_cost_delay</varname> as small as your platform
+         will consistently measure; large delays are not helpful.
         </para>
        </listitem>
       </varlistentry>
@@ -7020,7 +7023,7 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
      </varlistentry>
 
      <varlistentry id="guc-autovacuum-vacuum-cost-delay" xreflabel="autovacuum_vacuum_cost_delay">
-      <term><varname>autovacuum_vacuum_cost_delay</varname> (<type>integer</type>)
+      <term><varname>autovacuum_vacuum_cost_delay</varname> (<type>floating point</type>)
       <indexterm>
        <primary><varname>autovacuum_vacuum_cost_delay</varname> configuration parameter</primary>
       </indexterm>

doc/src/sgml/ref/create_table.sgml

@@ -1385,7 +1385,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
    </varlistentry>
 
    <varlistentry>
-    <term><literal>autovacuum_vacuum_cost_delay</literal>, <literal>toast.autovacuum_vacuum_cost_delay</literal> (<type>integer</type>)</term>
+    <term><literal>autovacuum_vacuum_cost_delay</literal>, <literal>toast.autovacuum_vacuum_cost_delay</literal> (<type>floating point</type>)</term>
     <listitem>
      <para>
       Per-table value for <xref linkend="guc-autovacuum-vacuum-cost-delay"/>

src/backend/access/common/reloptions.c

@@ -1198,7 +1198,7 @@ parse_one_reloption(relopt_value *option, char *text_str, int text_len,
 			{
 				relopt_real *optreal = (relopt_real *) option->gen;
 
-				parsed = parse_real(value, &option->values.real_val);
+				parsed = parse_real(value, &option->values.real_val, 0, NULL);
 				if (validate && !parsed)
 					ereport(ERROR,
 							(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -1359,8 +1359,6 @@ default_reloptions(Datum reloptions, bool validate, relopt_kind kind)
 		offsetof(StdRdOptions, autovacuum) + offsetof(AutoVacOpts, vacuum_threshold)},
 		{"autovacuum_analyze_threshold", RELOPT_TYPE_INT,
 		offsetof(StdRdOptions, autovacuum) + offsetof(AutoVacOpts, analyze_threshold)},
-		{"autovacuum_vacuum_cost_delay", RELOPT_TYPE_INT,
-		offsetof(StdRdOptions, autovacuum) + offsetof(AutoVacOpts, vacuum_cost_delay)},
 		{"autovacuum_vacuum_cost_limit", RELOPT_TYPE_INT,
 		offsetof(StdRdOptions, autovacuum) + offsetof(AutoVacOpts, vacuum_cost_limit)},
 		{"autovacuum_freeze_min_age", RELOPT_TYPE_INT,
@@ -1379,6 +1377,8 @@ default_reloptions(Datum reloptions, bool validate, relopt_kind kind)
 		offsetof(StdRdOptions, autovacuum) + offsetof(AutoVacOpts, log_min_duration)},
 		{"toast_tuple_target", RELOPT_TYPE_INT,
 		offsetof(StdRdOptions, toast_tuple_target)},
+		{"autovacuum_vacuum_cost_delay", RELOPT_TYPE_REAL,
+		offsetof(StdRdOptions, autovacuum) + offsetof(AutoVacOpts, vacuum_cost_delay)},
 		{"autovacuum_vacuum_scale_factor", RELOPT_TYPE_REAL,
 		offsetof(StdRdOptions, autovacuum) + offsetof(AutoVacOpts, vacuum_scale_factor)},
 		{"autovacuum_analyze_scale_factor", RELOPT_TYPE_REAL,

src/backend/commands/vacuum.c

@@ -1834,13 +1834,13 @@ vacuum_delay_point(void)
 	if (VacuumCostActive && !InterruptPending &&
 		VacuumCostBalance >= VacuumCostLimit)
 	{
-		int			msec;
+		double		msec;
 
 		msec = VacuumCostDelay * VacuumCostBalance / VacuumCostLimit;
 		if (msec > VacuumCostDelay * 4)
 			msec = VacuumCostDelay * 4;
 
-		pg_usleep(msec * 1000L);
+		pg_usleep((long) (msec * 1000));
 
 		VacuumCostBalance = 0;
 

src/backend/postmaster/autovacuum.c

@@ -120,7 +120,7 @@ double		autovacuum_anl_scale;
 int			autovacuum_freeze_max_age;
 int			autovacuum_multixact_freeze_max_age;
 
-int			autovacuum_vac_cost_delay;
+double		autovacuum_vac_cost_delay;
 int			autovacuum_vac_cost_limit;
 
 int			Log_autovacuum_min_duration = -1;
@@ -189,7 +189,7 @@ typedef struct autovac_table
 	Oid			at_relid;
 	int			at_vacoptions;	/* bitmask of VacuumOption */
 	VacuumParams at_params;
-	int			at_vacuum_cost_delay;
+	double		at_vacuum_cost_delay;
 	int			at_vacuum_cost_limit;
 	bool		at_dobalance;
 	bool		at_sharedrel;
@@ -225,7 +225,7 @@ typedef struct WorkerInfoData
 	TimestampTz wi_launchtime;
 	bool		wi_dobalance;
 	bool		wi_sharedrel;
-	int			wi_cost_delay;
+	double		wi_cost_delay;
 	int			wi_cost_limit;
 	int			wi_cost_limit_base;
 } WorkerInfoData;
@@ -1785,7 +1785,7 @@ autovac_balance_cost(void)
 	 */
 	int			vac_cost_limit = (autovacuum_vac_cost_limit > 0 ?
 								  autovacuum_vac_cost_limit : VacuumCostLimit);
-	int			vac_cost_delay = (autovacuum_vac_cost_delay >= 0 ?
+	double		vac_cost_delay = (autovacuum_vac_cost_delay >= 0 ?
 								  autovacuum_vac_cost_delay : VacuumCostDelay);
 	double		cost_total;
 	double		cost_avail;
@@ -1840,7 +1840,7 @@ autovac_balance_cost(void)
 		}
 
 		if (worker->wi_proc != NULL)
-			elog(DEBUG2, "autovac_balance_cost(pid=%u db=%u, rel=%u, dobalance=%s cost_limit=%d, cost_limit_base=%d, cost_delay=%d)",
+			elog(DEBUG2, "autovac_balance_cost(pid=%u db=%u, rel=%u, dobalance=%s cost_limit=%d, cost_limit_base=%d, cost_delay=%g)",
 				 worker->wi_proc->pid, worker->wi_dboid, worker->wi_tableoid,
 				 worker->wi_dobalance ? "yes" : "no",
 				 worker->wi_cost_limit, worker->wi_cost_limit_base,
@@ -2302,7 +2302,7 @@ do_autovacuum(void)
 		autovac_table *tab;
 		bool		isshared;
 		bool		skipit;
-		int			stdVacuumCostDelay;
+		double		stdVacuumCostDelay;
 		int			stdVacuumCostLimit;
 		dlist_iter	iter;
 
@@ -2831,7 +2831,7 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 		int			multixact_freeze_min_age;
 		int			multixact_freeze_table_age;
 		int			vac_cost_limit;
-		int			vac_cost_delay;
+		double		vac_cost_delay;
 		int			log_min_duration;
 
 		/*
@@ -2993,7 +2993,7 @@ relation_needs_vacanalyze(Oid relid,
 	 * table), or the autovacuum GUC variables.
 	 */
 
-	/* -1 in autovac setting means use plain vacuum_cost_delay */
+	/* -1 in autovac setting means use plain vacuum_scale_factor */
 	vac_scale_factor = (relopts && relopts->vacuum_scale_factor >= 0)
 		? relopts->vacuum_scale_factor
 		: autovacuum_vac_scale;

src/backend/utils/init/globals.c

@@ -138,7 +138,7 @@ int			VacuumCostPageHit = 1;	/* GUC parameters for vacuum */
 int			VacuumCostPageMiss = 10;
 int			VacuumCostPageDirty = 20;
 int			VacuumCostLimit = 2000;
-int			VacuumCostDelay = 0;
+double		VacuumCostDelay = 0;
 
 int			VacuumPageHit = 0;
 int			VacuumPageMiss = 0;