diff --git a/src/common/stringinfo.c b/src/common/stringinfo.c
index 55d2fbb864d..f4317003411 100644
--- a/src/common/stringinfo.c
+++ b/src/common/stringinfo.c
@@ -29,6 +29,40 @@
 #include "lib/stringinfo.h"
 
 
+/*
+ * initStringInfoInternal
+ *
+ * Initialize a StringInfoData struct (with previously undefined contents)
+ * to describe an empty string.
+ * The initial memory allocation size is specified by 'initsize'.
+ * The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+static inline void
+initStringInfoInternal(StringInfo str, int initsize)
+{
+	Assert(initsize >= 1 && initsize <= MaxAllocSize);
+
+	str->data = (char *) palloc(initsize);
+	str->maxlen = initsize;
+	resetStringInfo(str);
+}
+
+/*
+ * makeStringInfoInternal(int initsize)
+ *
+ * Create an empty 'StringInfoData' & return a pointer to it.
+ * The initial memory allocation size is specified by 'initsize'.
+ * The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+static inline StringInfo
+makeStringInfoInternal(int initsize)
+{
+	StringInfo	res = (StringInfo) palloc(sizeof(StringInfoData));
+
+	initStringInfoInternal(res, initsize);
+	return res;
+}
+
 /*
  * makeStringInfo
  *
@@ -37,13 +71,20 @@
 StringInfo
 makeStringInfo(void)
 {
-	StringInfo	res;
+	return makeStringInfoInternal(STRINGINFO_DEFAULT_SIZE);
+}
 
-	res = (StringInfo) palloc(sizeof(StringInfoData));
-
-	initStringInfo(res);
-
-	return res;
+/*
+ * makeStringInfoExt(int initsize)
+ *
+ * Create an empty 'StringInfoData' & return a pointer to it.
+ * The initial memory allocation size is specified by 'initsize'.
+ * The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+StringInfo
+makeStringInfoExt(int initsize)
+{
+	return makeStringInfoInternal(initsize);
 }
 
 /*
@@ -55,11 +96,21 @@ makeStringInfo(void)
 void
 initStringInfo(StringInfo str)
 {
-	int			size = 1024;	/* initial default buffer size */
+	return initStringInfoInternal(str, STRINGINFO_DEFAULT_SIZE);
+}
 
-	str->data = (char *) palloc(size);
-	str->maxlen = size;
-	resetStringInfo(str);
+/*
+ * initStringInfoExt
+ *
+ * Initialize a StringInfoData struct (with previously undefined contents)
+ * to describe an empty string.
+ * The initial memory allocation size is specified by 'initsize'.
+ * The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+void
+initStringInfoExt(StringInfo str, int initsize)
+{
+	initStringInfoInternal(str, initsize);
 }
 
 /*
diff --git a/src/include/lib/stringinfo.h b/src/include/lib/stringinfo.h
index 335208a9fda..c96df989bb0 100644
--- a/src/include/lib/stringinfo.h
+++ b/src/include/lib/stringinfo.h
@@ -55,11 +55,15 @@ typedef StringInfoData *StringInfo;
 
 
 /*------------------------
- * There are four ways to create a StringInfo object initially:
+ * There are six ways to create a StringInfo object initially:
  *
  * StringInfo stringptr = makeStringInfo();
  *		Both the StringInfoData and the data buffer are palloc'd.
  *
+ * StringInfo stringptr = makeStringInfoExt(initsize);
+ *		Same as makeStringInfo except the data buffer is allocated
+ *		with size 'initsize'.
+ *
  * StringInfoData string;
  * initStringInfo(&string);
  *		The data buffer is palloc'd but the StringInfoData is just local.
@@ -67,6 +71,11 @@ typedef StringInfoData *StringInfo;
  *		only live as long as the current routine.
  *
  * StringInfoData string;
+ * initStringInfoExt(&string, initsize);
+ *		Same as initStringInfo except the data buffer is allocated
+ *		with size 'initsize'.
+ *
+ * StringInfoData string;
  * initReadOnlyStringInfo(&string, existingbuf, len);
  *		The StringInfoData's data field is set to point directly to the
  *		existing buffer and the StringInfoData's len is set to the given len.
@@ -100,12 +109,22 @@ typedef StringInfoData *StringInfo;
  *-------------------------
  */
 
+#define STRINGINFO_DEFAULT_SIZE 1024	/* default initial allocation size */
+
 /*------------------------
  * makeStringInfo
  * Create an empty 'StringInfoData' & return a pointer to it.
  */
 extern StringInfo makeStringInfo(void);
 
+/*------------------------
+ * makeStringInfoExt
+ * Create an empty 'StringInfoData' & return a pointer to it.
+ * The data buffer is allocated with size 'initsize'.
+ * The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+extern StringInfo makeStringInfoExt(int initsize);
+
 /*------------------------
  * initStringInfo
  * Initialize a StringInfoData struct (with previously undefined contents)
@@ -113,6 +132,14 @@ extern StringInfo makeStringInfo(void);
  */
 extern void initStringInfo(StringInfo str);
 
+/*------------------------
+ * initStringInfoExt
+ * Initialize a StringInfoData struct (with previously undefined contents) to
+ * describe an empty string. The data buffer is allocated with size
+ * 'initsize'. The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+extern void initStringInfoExt(StringInfo str, int initsize);
+
 /*------------------------
  * initReadOnlyStringInfo
  * Initialize a StringInfoData struct from an existing string without copying