Speed up operations on numeric, mostly by avoiding palloc() overhead.

In many functions, a NumericVar was initialized from an input Numeric, to be
passed as input to a calculation function. When the NumericVar is not
modified, the digits array of the NumericVar can point directly to the digits
array in the original Numeric, and we can avoid a palloc() and memcpy(). Add
init_var_from_num() function to initialize a var like that.

Remove dscale argument from get_str_from_var(), as all the callers just
passed the dscale of the variable. That means that the rounding it used to
do was not actually necessary, and get_str_from_var() no longer scribbles on
its input. That makes it safer in general, and allows us to use the new
init_var_from_num() function in e.g numeric_out().

Also modified numericvar_to_int8() to no scribble on its input either. It
creates a temporary copy to avoid that. To compensate, the callers no longer
need to create a temporary copy, so the net # of pallocs is the same, but this
is nicer.

In the passing, use a constant for the number 10 in get_str_from_var_sci(),
when calculating 10^exponent. Saves a palloc() and some cycles to convert
integer 10 to numeric.

Original patch by Kyotaro HORIGUCHI, with further changes by me. Reviewed
by Pavel Stehule.

1 files changed, 104 insertions, 155 deletions

diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
index 68c1f1de3b7..b408df7faf4 100644
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -276,6 +276,16 @@ static NumericDigit const_two_data[1] = {2};
 static NumericVar const_two =
 {1, 0, NUMERIC_POS, 0, NULL, const_two_data};
 
+#if DEC_DIGITS == 4 || DEC_DIGITS == 2
+static NumericDigit const_ten_data[1] = {10};
+static NumericVar const_ten =
+{1, 0, NUMERIC_POS, 0, NULL, const_ten_data};
+#elif DEC_DIGITS == 1
+static NumericDigit const_ten_data[1] = {1};
+static NumericVar const_ten =
+{1, 1, NUMERIC_POS, 0, NULL, const_ten_data};
+#endif
+
 #if DEC_DIGITS == 4
 static NumericDigit const_zero_point_five_data[1] = {5000};
 #elif DEC_DIGITS == 2
@@ -367,8 +377,9 @@ static void zero_var(NumericVar *var);
 static const char *set_var_from_str(const char *str, const char *cp,
 				 NumericVar *dest);
 static void set_var_from_num(Numeric value, NumericVar *dest);
+static void init_var_from_num(Numeric num, NumericVar *dest);
 static void set_var_from_var(NumericVar *value, NumericVar *dest);
-static char *get_str_from_var(NumericVar *var, int dscale);
+static char *get_str_from_var(NumericVar *var);
 static char *get_str_from_var_sci(NumericVar *var, int rscale);
 
 static Numeric make_result(NumericVar *var);
@@ -533,18 +544,10 @@ numeric_out(PG_FUNCTION_ARGS)
 
 	/*
 	 * Get the number in the variable format.
-	 *
-	 * Even if we didn't need to change format, we'd still need to copy the
-	 * value to have a modifiable copy for rounding.  set_var_from_num() also
-	 * guarantees there is extra digit space in case we produce a carry out
-	 * from rounding.
 	 */
-	init_var(&x);
-	set_var_from_num(num, &x);
+	init_var_from_num(num, &x);
 
-	str = get_str_from_var(&x, x.dscale);
-
-	free_var(&x);
+	str = get_str_from_var(&x);
 
 	PG_RETURN_CSTRING(str);
 }
@@ -616,12 +619,10 @@ numeric_out_sci(Numeric num, int scale)
 	if (NUMERIC_IS_NAN(num))
 		return pstrdup("NaN");
 
-	init_var(&x);
-	set_var_from_num(num, &x);
+	init_var_from_num(num, &x);
 
 	str = get_str_from_var_sci(&x, scale);
 
-	free_var(&x);
 	return str;
 }
 
@@ -695,8 +696,7 @@ numeric_send(PG_FUNCTION_ARGS)
 	StringInfoData buf;
 	int			i;
 
-	init_var(&x);
-	set_var_from_num(num, &x);
+	init_var_from_num(num, &x);
 
 	pq_begintypsend(&buf);
 
@@ -707,8 +707,6 @@ numeric_send(PG_FUNCTION_ARGS)
 	for (i = 0; i < x.ndigits; i++)
 		pq_sendint(&buf, x.digits[i], sizeof(NumericDigit));
 
-	free_var(&x);
-
 	PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
 }
 
@@ -1150,9 +1148,7 @@ numeric_ceil(PG_FUNCTION_ARGS)
 	if (NUMERIC_IS_NAN(num))
 		PG_RETURN_NUMERIC(make_result(&const_nan));
 
-	init_var(&result);
-
-	set_var_from_num(num, &result);
+	init_var_from_num(num, &result);
 	ceil_var(&result, &result);
 
 	res = make_result(&result);
@@ -1177,9 +1173,7 @@ numeric_floor(PG_FUNCTION_ARGS)
 	if (NUMERIC_IS_NAN(num))
 		PG_RETURN_NUMERIC(make_result(&const_nan));
 
-	init_var(&result);
-
-	set_var_from_num(num, &result);
+	init_var_from_num(num, &result);
 	floor_var(&result, &result);
 
 	res = make_result(&result);
@@ -1282,13 +1276,9 @@ compute_bucket(Numeric operand, Numeric bound1, Numeric bound2,
 	NumericVar	bound2_var;
 	NumericVar	operand_var;
 
-	init_var(&bound1_var);
-	init_var(&bound2_var);
-	init_var(&operand_var);
-
-	set_var_from_num(bound1, &bound1_var);
-	set_var_from_num(bound2, &bound2_var);
-	set_var_from_num(operand, &operand_var);
+	init_var_from_num(bound1, &bound1_var);
+	init_var_from_num(bound2, &bound2_var);
+	init_var_from_num(operand, &operand_var);
 
 	if (cmp_var(&bound1_var, &bound2_var) < 0)
 	{
@@ -1573,19 +1563,14 @@ numeric_add(PG_FUNCTION_ARGS)
 	/*
 	 * Unpack the values, let add_var() compute the result and return it.
 	 */
-	init_var(&arg1);
-	init_var(&arg2);
-	init_var(&result);
-
-	set_var_from_num(num1, &arg1);
-	set_var_from_num(num2, &arg2);
+	init_var_from_num(num1, &arg1);
+	init_var_from_num(num2, &arg2);
 
+	init_var(&result);
 	add_var(&arg1, &arg2, &result);
 
 	res = make_result(&result);
 
-	free_var(&arg1);
-	free_var(&arg2);
 	free_var(&result);
 
 	PG_RETURN_NUMERIC(res);
@@ -1616,19 +1601,14 @@ numeric_sub(PG_FUNCTION_ARGS)
 	/*
 	 * Unpack the values, let sub_var() compute the result and return it.
 	 */
-	init_var(&arg1);
-	init_var(&arg2);
-	init_var(&result);
-
-	set_var_from_num(num1, &arg1);
-	set_var_from_num(num2, &arg2);
+	init_var_from_num(num1, &arg1);
+	init_var_from_num(num2, &arg2);
 
+	init_var(&result);
 	sub_var(&arg1, &arg2, &result);
 
 	res = make_result(&result);
 
-	free_var(&arg1);
-	free_var(&arg2);
 	free_var(&result);
 
 	PG_RETURN_NUMERIC(res);
@@ -1663,19 +1643,14 @@ numeric_mul(PG_FUNCTION_ARGS)
 	 * we request exact representation for the product (rscale = sum(dscale of
 	 * arg1, dscale of arg2)).
 	 */
-	init_var(&arg1);
-	init_var(&arg2);
-	init_var(&result);
-
-	set_var_from_num(num1, &arg1);
-	set_var_from_num(num2, &arg2);
+	init_var_from_num(num1, &arg1);
+	init_var_from_num(num2, &arg2);
 
+	init_var(&result);
 	mul_var(&arg1, &arg2, &result, arg1.dscale + arg2.dscale);
 
 	res = make_result(&result);
 
-	free_var(&arg1);
-	free_var(&arg2);
 	free_var(&result);
 
 	PG_RETURN_NUMERIC(res);
@@ -1707,12 +1682,10 @@ numeric_div(PG_FUNCTION_ARGS)
 	/*
 	 * Unpack the arguments
 	 */
-	init_var(&arg1);
-	init_var(&arg2);
-	init_var(&result);
+	init_var_from_num(num1, &arg1);
+	init_var_from_num(num2, &arg2);
 
-	set_var_from_num(num1, &arg1);
-	set_var_from_num(num2, &arg2);
+	init_var(&result);
 
 	/*
 	 * Select scale for division result
@@ -1726,8 +1699,6 @@ numeric_div(PG_FUNCTION_ARGS)
 
 	res = make_result(&result);
 
-	free_var(&arg1);
-	free_var(&arg2);
 	free_var(&result);
 
 	PG_RETURN_NUMERIC(res);
@@ -1758,12 +1729,10 @@ numeric_div_trunc(PG_FUNCTION_ARGS)
 	/*
 	 * Unpack the arguments
 	 */
-	init_var(&arg1);
-	init_var(&arg2);
-	init_var(&result);
+	init_var_from_num(num1, &arg1);
+	init_var_from_num(num2, &arg2);
 
-	set_var_from_num(num1, &arg1);
-	set_var_from_num(num2, &arg2);
+	init_var(&result);
 
 	/*
 	 * Do the divide and return the result
@@ -1772,8 +1741,6 @@ numeric_div_trunc(PG_FUNCTION_ARGS)
 
 	res = make_result(&result);
 
-	free_var(&arg1);
-	free_var(&arg2);
 	free_var(&result);
 
 	PG_RETURN_NUMERIC(res);
@@ -1798,20 +1765,16 @@ numeric_mod(PG_FUNCTION_ARGS)
 	if (NUMERIC_IS_NAN(num1) || NUMERIC_IS_NAN(num2))
 		PG_RETURN_NUMERIC(make_result(&const_nan));
 
-	init_var(&arg1);
-	init_var(&arg2);
-	init_var(&result);
+	init_var_from_num(num1, &arg1);
+	init_var_from_num(num2, &arg2);
 
-	set_var_from_num(num1, &arg1);
-	set_var_from_num(num2, &arg2);
+	init_var(&result);
 
 	mod_var(&arg1, &arg2, &result);
 
 	res = make_result(&result);
 
 	free_var(&result);
-	free_var(&arg2);
-	free_var(&arg1);
 
 	PG_RETURN_NUMERIC(res);
 }
@@ -1838,9 +1801,7 @@ numeric_inc(PG_FUNCTION_ARGS)
 	/*
 	 * Compute the result and return it
 	 */
-	init_var(&arg);
-
-	set_var_from_num(num, &arg);
+	init_var_from_num(num, &arg);
 
 	add_var(&arg, &const_one, &arg);
 
@@ -1977,10 +1938,9 @@ numeric_sqrt(PG_FUNCTION_ARGS)
 	 * to give at least NUMERIC_MIN_SIG_DIGITS significant digits; but in any
 	 * case not less than the input's dscale.
 	 */
-	init_var(&arg);
-	init_var(&result);
+	init_var_from_num(num, &arg);
 
-	set_var_from_num(num, &arg);
+	init_var(&result);
 
 	/* Assume the input was normalized, so arg.weight is accurate */
 	sweight = (arg.weight + 1) * DEC_DIGITS / 2 - 1;
@@ -1998,7 +1958,6 @@ numeric_sqrt(PG_FUNCTION_ARGS)
 	res = make_result(&result);
 
 	free_var(&result);
-	free_var(&arg);
 
 	PG_RETURN_NUMERIC(res);
 }
@@ -2030,10 +1989,9 @@ numeric_exp(PG_FUNCTION_ARGS)
 	 * to give at least NUMERIC_MIN_SIG_DIGITS significant digits; but in any
 	 * case not less than the input's dscale.
 	 */
-	init_var(&arg);
-	init_var(&result);
+	init_var_from_num(num, &arg);
 
-	set_var_from_num(num, &arg);
+	init_var(&result);
 
 	/* convert input to float8, ignoring overflow */
 	val = numericvar_to_double_no_overflow(&arg);
@@ -2061,7 +2019,6 @@ numeric_exp(PG_FUNCTION_ARGS)
 	res = make_result(&result);
 
 	free_var(&result);
-	free_var(&arg);
 
 	PG_RETURN_NUMERIC(res);
 }
@@ -2088,11 +2045,9 @@ numeric_ln(PG_FUNCTION_ARGS)
 	if (NUMERIC_IS_NAN(num))
 		PG_RETURN_NUMERIC(make_result(&const_nan));
 
-	init_var(&arg);
+	init_var_from_num(num, &arg);
 	init_var(&result);
 
-	set_var_from_num(num, &arg);
-
 	/* Approx decimal digits before decimal point */
 	dec_digits = (arg.weight + 1) * DEC_DIGITS;
 
@@ -2112,7 +2067,6 @@ numeric_ln(PG_FUNCTION_ARGS)
 	res = make_result(&result);
 
 	free_var(&result);
-	free_var(&arg);
 
 	PG_RETURN_NUMERIC(res);
 }
@@ -2142,13 +2096,10 @@ numeric_log(PG_FUNCTION_ARGS)
 	/*
 	 * Initialize things
 	 */
-	init_var(&arg1);
-	init_var(&arg2);
+	init_var_from_num(num1, &arg1);
+	init_var_from_num(num2, &arg2);
 	init_var(&result);
 
-	set_var_from_num(num1, &arg1);
-	set_var_from_num(num2, &arg2);
-
 	/*
 	 * Call log_var() to compute and return the result; note it handles scale
 	 * selection itself.
@@ -2158,8 +2109,6 @@ numeric_log(PG_FUNCTION_ARGS)
 	res = make_result(&result);
 
 	free_var(&result);
-	free_var(&arg2);
-	free_var(&arg1);
 
 	PG_RETURN_NUMERIC(res);
 }
@@ -2190,15 +2139,12 @@ numeric_power(PG_FUNCTION_ARGS)
 	/*
 	 * Initialize things
 	 */
-	init_var(&arg1);
-	init_var(&arg2);
 	init_var(&arg2_trunc);
 	init_var(&result);
+	init_var_from_num(num1, &arg1);
+	init_var_from_num(num2, &arg2);
 
-	set_var_from_num(num1, &arg1);
-	set_var_from_num(num2, &arg2);
 	set_var_from_var(&arg2, &arg2_trunc);
-
 	trunc_var(&arg2_trunc, 0);
 
 	/*
@@ -2227,9 +2173,7 @@ numeric_power(PG_FUNCTION_ARGS)
 	res = make_result(&result);
 
 	free_var(&result);
-	free_var(&arg2);
 	free_var(&arg2_trunc);
-	free_var(&arg1);
 
 	PG_RETURN_NUMERIC(res);
 }
@@ -2276,10 +2220,8 @@ numeric_int4(PG_FUNCTION_ARGS)
 				 errmsg("cannot convert NaN to integer")));
 
 	/* Convert to variable format, then convert to int4 */
-	init_var(&x);
-	set_var_from_num(num, &x);
+	init_var_from_num(num, &x);
 	result = numericvar_to_int4(&x);
-	free_var(&x);
 	PG_RETURN_INT32(result);
 }
 
@@ -2344,16 +2286,13 @@ numeric_int8(PG_FUNCTION_ARGS)
 				 errmsg("cannot convert NaN to bigint")));
 
 	/* Convert to variable format and thence to int8 */
-	init_var(&x);
-	set_var_from_num(num, &x);
+	init_var_from_num(num, &x);
 
 	if (!numericvar_to_int8(&x, &result))
 		ereport(ERROR,
 				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
 				 errmsg("bigint out of range")));
 
-	free_var(&x);
-
 	PG_RETURN_INT64(result);
 }
 
@@ -2392,16 +2331,13 @@ numeric_int2(PG_FUNCTION_ARGS)
 				 errmsg("cannot convert NaN to smallint")));
 
 	/* Convert to variable format and thence to int8 */
-	init_var(&x);
-	set_var_from_num(num, &x);
+	init_var_from_num(num, &x);
 
 	if (!numericvar_to_int8(&x, &val))
 		ereport(ERROR,
 				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
 				 errmsg("smallint out of range")));
 
-	free_var(&x);
-
 	/* Down-convert to int2 */
 	result = (int16) val;
 
@@ -2763,8 +2699,7 @@ numeric_stddev_internal(ArrayType *transarray,
 	if (NUMERIC_IS_NAN(N) || NUMERIC_IS_NAN(sumX) || NUMERIC_IS_NAN(sumX2))
 		return make_result(&const_nan);
 
-	init_var(&vN);
-	set_var_from_num(N, &vN);
+	init_var_from_num(N, &vN);
 
 	/*
 	 * Sample stddev and variance are undefined when N <= 1; population stddev
@@ -2777,7 +2712,6 @@ numeric_stddev_internal(ArrayType *transarray,
 
 	if (cmp_var(&vN, comp) <= 0)
 	{
-		free_var(&vN);
 		*is_null = true;
 		return NULL;
 	}
@@ -2785,10 +2719,8 @@ numeric_stddev_internal(ArrayType *transarray,
 	init_var(&vNminus1);
 	sub_var(&vN, &const_one, &vNminus1);
 
-	init_var(&vsumX);
-	set_var_from_num(sumX, &vsumX);
-	init_var(&vsumX2);
-	set_var_from_num(sumX2, &vsumX2);
+	init_var_from_num(sumX, &vsumX);
+	init_var_from_num(sumX2, &vsumX2);
 
 	/* compute rscale for mul_var calls */
 	rscale = vsumX.dscale * 2;
@@ -2816,7 +2748,6 @@ numeric_stddev_internal(ArrayType *transarray,
 		res = make_result(&vsumX);
 	}
 
-	free_var(&vN);
 	free_var(&vNminus1);
 	free_var(&vsumX);
 	free_var(&vsumX2);
@@ -3450,6 +3381,32 @@ set_var_from_num(Numeric num, NumericVar *dest)
 
 
 /*
+ * init_var_from_num() -
+ *
+ *	Initialize a variable from packed db format. The digits array is not
+ *	copied, which saves some cycles when the resulting var is not modified.
+ *	Also, there's no need to call free_var(), as long as you don't assign any
+ *	other value to it (with set_var_* functions, or by using the var as the
+ *	destination of a function like add_var())
+ *
+ *	CAUTION: Do not modify the digits buffer of a var initialized with this
+ *	function, e.g by calling round_var() or trunc_var(), as the changes will
+ *	propagate to the original Numeric! It's OK to use it as the destination
+ *	argument of one of the calculational functions, though.
+ */
+static void
+init_var_from_num(Numeric num, NumericVar *dest)
+{
+	dest->ndigits = NUMERIC_NDIGITS(num);
+	dest->weight = NUMERIC_WEIGHT(num);
+	dest->sign = NUMERIC_SIGN(num);
+	dest->dscale = NUMERIC_DSCALE(num);
+	dest->digits = NUMERIC_DIGITS(num);
+	dest->buf = NULL;	/* digits array is not palloc'd */
+}
+
+
+/*
  * set_var_from_var() -
  *
  *	Copy one variable into another
@@ -3475,12 +3432,13 @@ set_var_from_var(NumericVar *value, NumericVar *dest)
  * get_str_from_var() -
  *
  *	Convert a var to text representation (guts of numeric_out).
- *	CAUTION: var's contents may be modified by rounding!
+ *	The var is displayed to the number of digits indicated by its dscale.
  *	Returns a palloc'd string.
  */
 static char *
-get_str_from_var(NumericVar *var, int dscale)
+get_str_from_var(NumericVar *var)
 {
+	int			dscale;
 	char	   *str;
 	char	   *cp;
 	char	   *endcp;
@@ -3492,13 +3450,7 @@ get_str_from_var(NumericVar *var, int dscale)
 	NumericDigit d1;
 #endif
 
-	if (dscale < 0)
-		dscale = 0;
-
-	/*
-	 * Check if we must round up before printing the value and do so.
-	 */
-	round_var(var, dscale);
+	dscale = var->dscale;
 
 	/*
 	 * Allocate space for the result.
@@ -3634,8 +3586,6 @@ get_str_from_var(NumericVar *var, int dscale)
  *	rscale is the number of decimal digits desired after the decimal point in
  *	the output, negative values will be treated as meaning zero.
  *
- *	CAUTION: var's contents may be modified by rounding!
- *
  *	Returns a palloc'd string.
  */
 static char *
@@ -3694,10 +3644,9 @@ get_str_from_var_sci(NumericVar *var, int rscale)
 	init_var(&denominator);
 	init_var(&significand);
 
-	int8_to_numericvar((int64) 10, &denominator);
-	power_var_int(&denominator, exponent, &denominator, denom_scale);
+	power_var_int(&const_ten, exponent, &denominator, denom_scale);
 	div_var(var, &denominator, &significand, rscale, true);
-	sig_out = get_str_from_var(&significand, rscale);
+	sig_out = get_str_from_var(&significand);
 
 	free_var(&denominator);
 	free_var(&significand);
@@ -3886,8 +3835,6 @@ apply_typmod(NumericVar *var, int32 typmod)
  * Convert numeric to int8, rounding if needed.
  *
  * If overflow, return FALSE (no error is raised).	Return TRUE if okay.
- *
- *	CAUTION: var's contents may be modified by rounding!
  */
 static bool
 numericvar_to_int8(NumericVar *var, int64 *result)
@@ -3899,16 +3846,20 @@ numericvar_to_int8(NumericVar *var, int64 *result)
 	int64		val,
 				oldval;
 	bool		neg;
+	NumericVar	rounded;
 
 	/* Round to nearest integer */
-	round_var(var, 0);
+	init_var(&rounded);
+	set_var_from_var(var, &rounded);
+	round_var(&rounded, 0);
 
 	/* Check for zero input */
-	strip_var(var);
-	ndigits = var->ndigits;
+	strip_var(&rounded);
+	ndigits = rounded.ndigits;
 	if (ndigits == 0)
 	{
 		*result = 0;
+		free_var(&rounded);
 		return true;
 	}
 
@@ -3916,12 +3867,12 @@ numericvar_to_int8(NumericVar *var, int64 *result)
 	 * For input like 10000000000, we must treat stripped digits as real. So
 	 * the loop assumes there are weight+1 digits before the decimal point.
 	 */
-	weight = var->weight;
+	weight = rounded.weight;
 	Assert(weight >= 0 && ndigits <= weight + 1);
 
 	/* Construct the result */
-	digits = var->digits;
-	neg = (var->sign == NUMERIC_NEG);
+	digits = rounded.digits;
+	neg = (rounded.sign == NUMERIC_NEG);
 	val = digits[0];
 	for (i = 1; i <= weight; i++)
 	{
@@ -3940,10 +3891,15 @@ numericvar_to_int8(NumericVar *var, int64 *result)
 		if ((val / NBASE) != oldval)	/* possible overflow? */
 		{
 			if (!neg || (-val) != val || val == 0 || oldval < 0)
+			{
+				free_var(&rounded);
 				return false;
+			}
 		}
 	}
 
+	free_var(&rounded);
+
 	*result = neg ? -val : val;
 	return true;
 }
@@ -4030,7 +3986,7 @@ numericvar_to_double_no_overflow(NumericVar *var)
 	double		val;
 	char	   *endptr;
 
-	tmp = get_str_from_var(var, var->dscale);
+	tmp = get_str_from_var(var);
 
 	/* unlike float8in, we ignore ERANGE from strtod */
 	val = strtod(tmp, &endptr);
@@ -5597,13 +5553,9 @@ power_var(NumericVar *base, NumericVar *exp, NumericVar *result)
 	if (exp->ndigits == 0 || exp->ndigits <= exp->weight + 1)
 	{
 		/* exact integer, but does it fit in int? */
-		NumericVar	x;
 		int64		expval64;
 
-		/* must copy because numericvar_to_int8() scribbles on input */
-		init_var(&x);
-		set_var_from_var(exp, &x);
-		if (numericvar_to_int8(&x, &expval64))
+		if (numericvar_to_int8(exp, &expval64))
 		{
 			int			expval = (int) expval64;
 
@@ -5617,12 +5569,9 @@ power_var(NumericVar *base, NumericVar *exp, NumericVar *result)
 				rscale = Min(rscale, NUMERIC_MAX_DISPLAY_SCALE);
 
 				power_var_int(base, expval, result, rscale);
-
-				free_var(&x);
 				return;
 			}
 		}
-		free_var(&x);
 	}
 
 	/*