Use appendStringInfoSpaces in more places

david-rowley · david-rowley · commit 9f1ca6ce6596 · 2023-01-20T13:07:24.000+13:00
This adjusts a few places which were appending a string constant containing spaces onto a StringInfo. We have appendStringInfoSpaces for that job, so let's use that instead. For the change to jsonb.c's add_indent() function, appendStringInfoString was being called inside a loop to append 4 spaces on each loop. This meant that enlargeStringInfo would get called once per loop. Here it should be much more efficient to get rid of the loop and just calculate the number of spaces with "level * 4" and just append all the spaces in one go. Here we additionally adjust the appendStringInfoSpaces function so it makes use of memset rather than a while loop to apply the required spaces to the StringInfo. One of the problems with the while loop was that it was incrementing one variable and decrementing another variable once per loop. That's more work than what's required to get the job done. We may as well use memset for this rather than trying to optimize the existing loop. Some testing has shown memset is faster even for very small sizes. Discussion: https://postgr.es/m/CAApHDvp_rKkvwudBKgBHniNRg67bzXVjyvVKfX0G2zS967K43A@mail.gmail.com
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
@@ -3324,7 +3324,7 @@ show_hashagg_info(AggState *aggstate, ExplainState *es)
 			if (!gotone)
 				ExplainIndentText(es);
 			else
-				appendStringInfoString(es->str, "  ");
+				appendStringInfoSpaces(es->str, 2);
 
 			appendStringInfo(es->str, "Batches: %d  Memory Usage: " INT64_FORMAT "kB",
 							 aggstate->hash_batches_used, memPeakKb);
diff --git a/src/backend/utils/adt/jsonb.c b/src/backend/utils/adt/jsonb.c
@@ -626,11 +626,8 @@ add_indent(StringInfo out, bool indent, int level)
 {
 	if (indent)
 	{
-		int			i;
-
 		appendStringInfoCharMacro(out, '\n');
-		for (i = 0; i < level; i++)
-			appendBinaryStringInfo(out, "    ", 4);
+		appendStringInfoSpaces(out, level * 4);
 	}
 }
 
diff --git a/src/common/stringinfo.c b/src/common/stringinfo.c
@@ -211,8 +211,8 @@ appendStringInfoSpaces(StringInfo str, int count)
 		enlargeStringInfo(str, count);
 
 		/* OK, append the spaces */
-		while (--count >= 0)
-			str->data[str->len++] = ' ';
+		memset(&str->data[str->len], ' ', count);
+		str->len += count;
 		str->data[str->len] = '\0';
 	}
 }

Original file line number	Diff line number	Diff line change
`@@ -626,11 +626,8 @@ add_indent(StringInfo out, bool indent, int level)`
`626`	`626`	`{`
`627`	`627`	`if (indent)`
`628`	`628`	`{`
`629`		`- int i;`
`630`		`-`
`631`	`629`	`appendStringInfoCharMacro(out, '\n');`
`632`		`- for (i = 0; i < level; i++)`
`633`		`- appendBinaryStringInfo(out, " ", 4);`
	`630`	`+ appendStringInfoSpaces(out, level * 4);`
`634`	`631`	`}`
`635`	`632`	`}`
`636`	`633`
Original file line number	Diff line number	Diff line change
`@@ -211,8 +211,8 @@ appendStringInfoSpaces(StringInfo str, int count)`
`211`	`211`	`enlargeStringInfo(str, count);`
`212`	`212`
`213`	`213`	`/* OK, append the spaces */`
`214`		`- while (--count >= 0)`
`215`		`- str->data[str->len++] = ' ';`
	`214`	`+ memset(&str->data[str->len], ' ', count);`
	`215`	`+ str->len += count;`
`216`	`216`	`str->data[str->len] = '\0';`
`217`	`217`	`}`
`218`	`218`	`}`