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

1 files changed, 204 insertions, 123 deletions

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 712c821dfb0..6e396f1598f 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -755,13 +755,13 @@ const char *const config_type_names[] =
  * For each supported conversion from one unit to another, we have an entry
  * in the table.
  *
- * To keep things simple, and to avoid intermediate-value overflows,
+ * To keep things simple, and to avoid possible roundoff error,
  * conversions are never chained.  There needs to be a direct conversion
  * between all units (of the same type).
  *
- * The conversions from each base unit must be kept in order from greatest
- * to smallest unit; convert_from_base_unit() relies on that.  (The order of
- * the base units does not matter.)
+ * The conversions for each base unit must be kept in order from greatest to
+ * smallest human-friendly unit; convert_xxx_from_base_unit() rely on that.
+ * (The order of the base-unit groups does not matter.)
  */
 #define MAX_UNIT_LEN		3	/* length of longest recognized unit string */
 
@@ -770,9 +770,7 @@ typedef struct
 	char		unit[MAX_UNIT_LEN + 1]; /* unit, as a string, like "kB" or
 										 * "min" */
 	int			base_unit;		/* GUC_UNIT_XXX */
-	int64		multiplier;		/* If positive, multiply the value with this
-								 * for unit -> base_unit conversion.  If
-								 * negative, divide (with the absolute value) */
+	double		multiplier;		/* Factor for converting unit -> base_unit */
 } unit_conversion;
 
 /* Ensure that the constants in the tables don't overflow or underflow */
@@ -787,45 +785,40 @@ static const char *memory_units_hint = gettext_noop("Valid units for this parame
 
 static const unit_conversion memory_unit_conversion_table[] =
 {
-	/*
-	 * TB -> bytes conversion always overflows 32-bit integer, so this always
-	 * produces an error.  Include it nevertheless for completeness, and so
-	 * that you get an "out of range" error, rather than "invalid unit".
-	 */
-	{"TB", GUC_UNIT_BYTE, INT64CONST(1024) * 1024 * 1024 * 1024},
-	{"GB", GUC_UNIT_BYTE, 1024 * 1024 * 1024},
-	{"MB", GUC_UNIT_BYTE, 1024 * 1024},
-	{"kB", GUC_UNIT_BYTE, 1024},
-	{"B", GUC_UNIT_BYTE, 1},
-
-	{"TB", GUC_UNIT_KB, 1024 * 1024 * 1024},
-	{"GB", GUC_UNIT_KB, 1024 * 1024},
-	{"MB", GUC_UNIT_KB, 1024},
-	{"kB", GUC_UNIT_KB, 1},
-	{"B", GUC_UNIT_KB, -1024},
-
-	{"TB", GUC_UNIT_MB, 1024 * 1024},
-	{"GB", GUC_UNIT_MB, 1024},
-	{"MB", GUC_UNIT_MB, 1},
-	{"kB", GUC_UNIT_MB, -1024},
-	{"B", GUC_UNIT_MB, -(1024 * 1024)},
-
-	{"TB", GUC_UNIT_BLOCKS, (1024 * 1024 * 1024) / (BLCKSZ / 1024)},
-	{"GB", GUC_UNIT_BLOCKS, (1024 * 1024) / (BLCKSZ / 1024)},
-	{"MB", GUC_UNIT_BLOCKS, 1024 / (BLCKSZ / 1024)},
-	{"kB", GUC_UNIT_BLOCKS, -(BLCKSZ / 1024)},
-	{"B", GUC_UNIT_BLOCKS, -BLCKSZ},
-
-	{"TB", GUC_UNIT_XBLOCKS, (1024 * 1024 * 1024) / (XLOG_BLCKSZ / 1024)},
-	{"GB", GUC_UNIT_XBLOCKS, (1024 * 1024) / (XLOG_BLCKSZ / 1024)},
-	{"MB", GUC_UNIT_XBLOCKS, 1024 / (XLOG_BLCKSZ / 1024)},
-	{"kB", GUC_UNIT_XBLOCKS, -(XLOG_BLCKSZ / 1024)},
-	{"B", GUC_UNIT_XBLOCKS, -XLOG_BLCKSZ},
+	{"TB", GUC_UNIT_BYTE, 1024.0 * 1024.0 * 1024.0 * 1024.0},
+	{"GB", GUC_UNIT_BYTE, 1024.0 * 1024.0 * 1024.0},
+	{"MB", GUC_UNIT_BYTE, 1024.0 * 1024.0},
+	{"kB", GUC_UNIT_BYTE, 1024.0},
+	{"B", GUC_UNIT_BYTE, 1.0},
+
+	{"TB", GUC_UNIT_KB, 1024.0 * 1024.0 * 1024.0},
+	{"GB", GUC_UNIT_KB, 1024.0 * 1024.0},
+	{"MB", GUC_UNIT_KB, 1024.0},
+	{"kB", GUC_UNIT_KB, 1.0},
+	{"B", GUC_UNIT_KB, 1.0 / 1024.0},
+
+	{"TB", GUC_UNIT_MB, 1024.0 * 1024.0},
+	{"GB", GUC_UNIT_MB, 1024.0},
+	{"MB", GUC_UNIT_MB, 1.0},
+	{"kB", GUC_UNIT_MB, 1.0 / 1024.0},
+	{"B", GUC_UNIT_MB, 1.0 / (1024.0 * 1024.0)},
+
+	{"TB", GUC_UNIT_BLOCKS, (1024.0 * 1024.0 * 1024.0) / (BLCKSZ / 1024)},
+	{"GB", GUC_UNIT_BLOCKS, (1024.0 * 1024.0) / (BLCKSZ / 1024)},
+	{"MB", GUC_UNIT_BLOCKS, 1024.0 / (BLCKSZ / 1024)},
+	{"kB", GUC_UNIT_BLOCKS, 1.0 / (BLCKSZ / 1024)},
+	{"B", GUC_UNIT_BLOCKS, 1.0 / BLCKSZ},
+
+	{"TB", GUC_UNIT_XBLOCKS, (1024.0 * 1024.0 * 1024.0) / (XLOG_BLCKSZ / 1024)},
+	{"GB", GUC_UNIT_XBLOCKS, (1024.0 * 1024.0) / (XLOG_BLCKSZ / 1024)},
+	{"MB", GUC_UNIT_XBLOCKS, 1024.0 / (XLOG_BLCKSZ / 1024)},
+	{"kB", GUC_UNIT_XBLOCKS, 1.0 / (XLOG_BLCKSZ / 1024)},
+	{"B", GUC_UNIT_XBLOCKS, 1.0 / XLOG_BLCKSZ},
 
 	{""}						/* end of table marker */
 };
 
-static const char *time_units_hint = gettext_noop("Valid units for this parameter are \"ms\", \"s\", \"min\", \"h\", and \"d\".");
+static const char *time_units_hint = gettext_noop("Valid units for this parameter are \"us\", \"ms\", \"s\", \"min\", \"h\", and \"d\".");
 
 static const unit_conversion time_unit_conversion_table[] =
 {
@@ -834,18 +827,21 @@ static const unit_conversion time_unit_conversion_table[] =
 	{"min", GUC_UNIT_MS, 1000 * 60},
 	{"s", GUC_UNIT_MS, 1000},
 	{"ms", GUC_UNIT_MS, 1},
+	{"us", GUC_UNIT_MS, 1.0 / 1000},
 
 	{"d", GUC_UNIT_S, 60 * 60 * 24},
 	{"h", GUC_UNIT_S, 60 * 60},
 	{"min", GUC_UNIT_S, 60},
 	{"s", GUC_UNIT_S, 1},
-	{"ms", GUC_UNIT_S, -1000},
+	{"ms", GUC_UNIT_S, 1.0 / 1000},
+	{"us", GUC_UNIT_S, 1.0 / (1000 * 1000)},
 
 	{"d", GUC_UNIT_MIN, 60 * 24},
 	{"h", GUC_UNIT_MIN, 60},
 	{"min", GUC_UNIT_MIN, 1},
-	{"s", GUC_UNIT_MIN, -60},
-	{"ms", GUC_UNIT_MIN, -1000 * 60},
+	{"s", GUC_UNIT_MIN, 1.0 / 60},
+	{"ms", GUC_UNIT_MIN, 1.0 / (1000 * 60)},
+	{"us", GUC_UNIT_MIN, 1.0 / (1000 * 1000 * 60)},
 
 	{""}						/* end of table marker */
 };
@@ -2274,28 +2270,6 @@ static struct config_int ConfigureNamesInt[] =
 	},
 
 	{
-		{"vacuum_cost_delay", PGC_USERSET, RESOURCES_VACUUM_DELAY,
-			gettext_noop("Vacuum cost delay in milliseconds."),
-			NULL,
-			GUC_UNIT_MS
-		},
-		&VacuumCostDelay,
-		0, 0, 100,
-		NULL, NULL, NULL
-	},
-
-	{
-		{"autovacuum_vacuum_cost_delay", PGC_SIGHUP, AUTOVACUUM,
-			gettext_noop("Vacuum cost delay in milliseconds, for autovacuum."),
-			NULL,
-			GUC_UNIT_MS
-		},
-		&autovacuum_vac_cost_delay,
-		20, -1, 100,
-		NULL, NULL, NULL
-	},
-
-	{
 		{"autovacuum_vacuum_cost_limit", PGC_SIGHUP, AUTOVACUUM,
 			gettext_noop("Vacuum cost amount available before napping, for autovacuum."),
 			NULL
@@ -3321,6 +3295,28 @@ static struct config_real ConfigureNamesReal[] =
 	},
 
 	{
+		{"vacuum_cost_delay", PGC_USERSET, RESOURCES_VACUUM_DELAY,
+			gettext_noop("Vacuum cost delay in milliseconds."),
+			NULL,
+			GUC_UNIT_MS
+		},
+		&VacuumCostDelay,
+		0, 0, 100,
+		NULL, NULL, NULL
+	},
+
+	{
+		{"autovacuum_vacuum_cost_delay", PGC_SIGHUP, AUTOVACUUM,
+			gettext_noop("Vacuum cost delay in milliseconds, for autovacuum."),
+			NULL,
+			GUC_UNIT_MS
+		},
+		&autovacuum_vac_cost_delay,
+		20, -1, 100,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"autovacuum_vacuum_scale_factor", PGC_SIGHUP, AUTOVACUUM,
 			gettext_noop("Number of tuple updates or deletes prior to vacuum as a fraction of reltuples."),
 			NULL
@@ -5960,17 +5956,35 @@ ReportGUCOption(struct config_generic *record)
 /*
  * Convert a value from one of the human-friendly units ("kB", "min" etc.)
  * to the given base unit.  'value' and 'unit' are the input value and unit
- * to convert from.  The converted value is stored in *base_value.
+ * to convert from (there can be trailing spaces in the unit string).
+ * The converted value is stored in *base_value.
+ * It's caller's responsibility to round off the converted value as necessary
+ * and check for out-of-range.
  *
  * Returns true on success, false if the input unit is not recognized.
  */
 static bool
-convert_to_base_unit(int64 value, const char *unit,
-					 int base_unit, int64 *base_value)
+convert_to_base_unit(double value, const char *unit,
+					 int base_unit, double *base_value)
 {
+	char		unitstr[MAX_UNIT_LEN + 1];
+	int			unitlen;
 	const unit_conversion *table;
 	int			i;
 
+	/* extract unit string to compare to table entries */
+	unitlen = 0;
+	while (*unit != '\0' && !isspace((unsigned char) *unit) &&
+		   unitlen < MAX_UNIT_LEN)
+		unitstr[unitlen++] = *(unit++);
+	unitstr[unitlen] = '\0';
+	/* allow whitespace after unit */
+	while (isspace((unsigned char) *unit))
+		unit++;
+	if (*unit != '\0')
+		return false;			/* unit too long, or garbage after it */
+
+	/* now search the appropriate table */
 	if (base_unit & GUC_UNIT_MEMORY)
 		table = memory_unit_conversion_table;
 	else
@@ -5979,12 +5993,9 @@ convert_to_base_unit(int64 value, const char *unit,
 	for (i = 0; *table[i].unit; i++)
 	{
 		if (base_unit == table[i].base_unit &&
-			strcmp(unit, table[i].unit) == 0)
+			strcmp(unitstr, table[i].unit) == 0)
 		{
-			if (table[i].multiplier < 0)
-				*base_value = value / (-table[i].multiplier);
-			else
-				*base_value = value * table[i].multiplier;
+			*base_value = value * table[i].multiplier;
 			return true;
 		}
 	}
@@ -5992,14 +6003,15 @@ convert_to_base_unit(int64 value, const char *unit,
 }
 
 /*
- * Convert a value in some base unit to a human-friendly unit.  The output
- * unit is chosen so that it's the greatest unit that can represent the value
- * without loss.  For example, if the base unit is GUC_UNIT_KB, 1024 is
- * converted to 1 MB, but 1025 is represented as 1025 kB.
+ * Convert an integer value in some base unit to a human-friendly unit.
+ *
+ * The output unit is chosen so that it's the greatest unit that can represent
+ * the value without loss.  For example, if the base unit is GUC_UNIT_KB, 1024
+ * is converted to 1 MB, but 1025 is represented as 1025 kB.
  */
 static void
-convert_from_base_unit(int64 base_value, int base_unit,
-					   int64 *value, const char **unit)
+convert_int_from_base_unit(int64 base_value, int base_unit,
+						   int64 *value, const char **unit)
 {
 	const unit_conversion *table;
 	int			i;
@@ -6016,22 +6028,62 @@ convert_from_base_unit(int64 base_value, int base_unit,
 		if (base_unit == table[i].base_unit)
 		{
 			/*
-			 * Accept the first conversion that divides the value evenly. We
+			 * Accept the first conversion that divides the value evenly.  We
 			 * assume that the conversions for each base unit are ordered from
 			 * greatest unit to the smallest!
 			 */
-			if (table[i].multiplier < 0)
+			if (table[i].multiplier <= 1.0 ||
+				base_value % (int64) table[i].multiplier == 0)
 			{
-				*value = base_value * (-table[i].multiplier);
+				*value = (int64) rint(base_value / table[i].multiplier);
 				*unit = table[i].unit;
 				break;
 			}
-			else if (base_value % table[i].multiplier == 0)
-			{
-				*value = base_value / table[i].multiplier;
-				*unit = table[i].unit;
+		}
+	}
+
+	Assert(*unit != NULL);
+}
+
+/*
+ * Convert a floating-point value in some base unit to a human-friendly unit.
+ *
+ * Same as above, except we have to do the math a bit differently, and
+ * there's a possibility that we don't find any exact divisor.
+ */
+static void
+convert_real_from_base_unit(double base_value, int base_unit,
+							double *value, const char **unit)
+{
+	const unit_conversion *table;
+	int			i;
+
+	*unit = NULL;
+
+	if (base_unit & GUC_UNIT_MEMORY)
+		table = memory_unit_conversion_table;
+	else
+		table = time_unit_conversion_table;
+
+	for (i = 0; *table[i].unit; i++)
+	{
+		if (base_unit == table[i].base_unit)
+		{
+			/*
+			 * Accept the first conversion that divides the value evenly; or
+			 * if there is none, use the smallest (last) target unit.
+			 *
+			 * What we actually care about here is whether snprintf with "%g"
+			 * will print the value as an integer, so the obvious test of
+			 * "*value == rint(*value)" is too strict; roundoff error might
+			 * make us choose an unreasonably small unit.  As a compromise,
+			 * accept a divisor that is within 1e-8 of producing an integer.
+			 */
+			*value = base_value / table[i].multiplier;
+			*unit = table[i].unit;
+			if (*value > 0 &&
+				fabs((rint(*value) / *value) - 1.0) <= 1e-8)
 				break;
-			}
 		}
 	}
 
@@ -6095,7 +6147,7 @@ get_config_unit_name(int flags)
  * If the string parses okay, return true, else false.
  * If okay and result is not NULL, return the value in *result.
  * If not okay and hintmsg is not NULL, *hintmsg is set to a suitable
- *	HINT message, or NULL if no hint provided.
+ * HINT message, or NULL if no hint provided.
  */
 bool
 parse_int(const char *value, int *result, int flags, const char **hintmsg)
@@ -6130,26 +6182,14 @@ parse_int(const char *value, int *result, int flags, const char **hintmsg)
 	/* Handle possible unit */
 	if (*endptr != '\0')
 	{
-		char		unit[MAX_UNIT_LEN + 1];
-		int			unitlen;
-		bool		converted = false;
+		double		cval;
 
 		if ((flags & GUC_UNIT) == 0)
 			return false;		/* this setting does not accept a unit */
 
-		unitlen = 0;
-		while (*endptr != '\0' && !isspace((unsigned char) *endptr) &&
-			   unitlen < MAX_UNIT_LEN)
-			unit[unitlen++] = *(endptr++);
-		unit[unitlen] = '\0';
-		/* allow whitespace after unit */
-		while (isspace((unsigned char) *endptr))
-			endptr++;
-
-		if (*endptr == '\0')
-			converted = convert_to_base_unit(val, unit, (flags & GUC_UNIT),
-											 &val);
-		if (!converted)
+		if (!convert_to_base_unit((double) val,
+								  endptr, (flags & GUC_UNIT),
+								  &cval))
 		{
 			/* invalid unit, or garbage after the unit; set hint and fail. */
 			if (hintmsg)
@@ -6162,13 +6202,15 @@ parse_int(const char *value, int *result, int flags, const char **hintmsg)
 			return false;
 		}
 
-		/* Check for overflow due to units conversion */
-		if (val != (int64) ((int32) val))
+		/* Round to int, then check for overflow due to units conversion */
+		cval = rint(cval);
+		if (cval > INT_MAX || cval < INT_MIN)
 		{
 			if (hintmsg)
 				*hintmsg = gettext_noop("Value exceeds integer range.");
 			return false;
 		}
+		val = (int64) cval;
 	}
 
 	if (result)
@@ -6180,32 +6222,59 @@ parse_int(const char *value, int *result, int flags, const char **hintmsg)
 
 /*
  * Try to parse value as a floating point number in the usual format.
+ *
  * If the string parses okay, return true, else false.
  * If okay and result is not NULL, return the value in *result.
+ * If not okay and hintmsg is not NULL, *hintmsg is set to a suitable
+ * HINT message, or NULL if no hint provided.
  */
 bool
-parse_real(const char *value, double *result)
+parse_real(const char *value, double *result, int flags, const char **hintmsg)
 {
 	double		val;
 	char	   *endptr;
 
+	/* To suppress compiler warnings, always set output params */
 	if (result)
-		*result = 0;			/* suppress compiler warning */
+		*result = 0;
+	if (hintmsg)
+		*hintmsg = NULL;
 
 	errno = 0;
 	val = strtod(value, &endptr);
+
 	if (endptr == value || errno == ERANGE)
-		return false;
+		return false;			/* no HINT for these cases */
 
 	/* reject NaN (infinities will fail range checks later) */
 	if (isnan(val))
-		return false;
+		return false;			/* treat same as syntax error; no HINT */
 
-	/* allow whitespace after number */
+	/* allow whitespace between number and unit */
 	while (isspace((unsigned char) *endptr))
 		endptr++;
+
+	/* Handle possible unit */
 	if (*endptr != '\0')
-		return false;
+	{
+		if ((flags & GUC_UNIT) == 0)
+			return false;		/* this setting does not accept a unit */
+
+		if (!convert_to_base_unit(val,
+								  endptr, (flags & GUC_UNIT),
+								  &val))
+		{
+			/* invalid unit, or garbage after the unit; set hint and fail. */
+			if (hintmsg)
+			{
+				if (flags & GUC_UNIT_MEMORY)
+					*hintmsg = memory_units_hint;
+				else
+					*hintmsg = time_units_hint;
+			}
+			return false;
+		}
+	}
 
 	if (result)
 		*result = val;
@@ -6393,13 +6462,16 @@ parse_and_validate_value(struct config_generic *record,
 		case PGC_REAL:
 			{
 				struct config_real *conf = (struct config_real *) record;
+				const char *hintmsg;
 
-				if (!parse_real(value, &newval->realval))
+				if (!parse_real(value, &newval->realval,
+								conf->gen.flags, &hintmsg))
 				{
 					ereport(elevel,
 							(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-							 errmsg("parameter \"%s\" requires a numeric value",
-									name)));
+							 errmsg("invalid value for parameter \"%s\": \"%s\"",
+									name, value),
+							 hintmsg ? errhint("%s", _(hintmsg)) : 0));
 					return false;
 				}
 
@@ -9278,10 +9350,9 @@ _ShowOption(struct config_generic *record, bool use_units)
 					const char *unit;
 
 					if (use_units && result > 0 && (record->flags & GUC_UNIT))
-					{
-						convert_from_base_unit(result, record->flags & GUC_UNIT,
-											   &result, &unit);
-					}
+						convert_int_from_base_unit(result,
+												   record->flags & GUC_UNIT,
+												   &result, &unit);
 					else
 						unit = "";
 
@@ -9300,8 +9371,18 @@ _ShowOption(struct config_generic *record, bool use_units)
 					val = conf->show_hook();
 				else
 				{
-					snprintf(buffer, sizeof(buffer), "%g",
-							 *conf->variable);
+					double		result = *conf->variable;
+					const char *unit;
+
+					if (use_units && result > 0 && (record->flags & GUC_UNIT))
+						convert_real_from_base_unit(result,
+													record->flags & GUC_UNIT,
+													&result, &unit);
+					else
+						unit = "";
+
+					snprintf(buffer, sizeof(buffer), "%g%s",
+							 result, unit);
 					val = buffer;
 				}
 			}