From c92d96ea219dceeb510927395bdc49787521c536 Mon Sep 17 00:00:00 2001
From: Andy Fan <zhihuifan1213@163.com>
Date: Tue, 29 Oct 2024 14:05:05 +0800
Subject: [PATCH v3 1/1] Using more specific code when detoasting an expanded
 datum.

In the detoast_attr/detoast_attr_slice function,
VARATT_IS_EXTERNAL_ONDISK and VARATT_IS_EXTERNAL_INDIRECT are checked
first, and then VARATT_IS_EXTERNAL_EXPANDED, however when it's true,
detoast_external_attr is called which checks the two cases again.
The attached patch uses a more specific code to handle this.
---
 src/backend/access/common/detoast.c | 48 ++++++++++++++++++-----------
 1 file changed, 30 insertions(+), 18 deletions(-)

diff --git a/src/backend/access/common/detoast.c b/src/backend/access/common/detoast.c
index d92e683384..249a4544de 100644
--- a/src/backend/access/common/detoast.c
+++ b/src/backend/access/common/detoast.c
@@ -28,6 +28,7 @@ static struct varlena *toast_fetch_datum_slice(struct varlena *attr,
 											   int32 slicelength);
 static struct varlena *toast_decompress_datum(struct varlena *attr);
 static struct varlena *toast_decompress_datum_slice(struct varlena *attr, int32 slicelength);
+static struct varlena *toast_EOH_datum(struct varlena *attr);
 
 /* ----------
  * detoast_external_attr -
@@ -79,16 +80,7 @@ detoast_external_attr(struct varlena *attr)
 	}
 	else if (VARATT_IS_EXTERNAL_EXPANDED(attr))
 	{
-		/*
-		 * This is an expanded-object pointer --- get flat format
-		 */
-		ExpandedObjectHeader *eoh;
-		Size		resultsize;
-
-		eoh = DatumGetEOHP(PointerGetDatum(attr));
-		resultsize = EOH_get_flat_size(eoh);
-		result = (struct varlena *) palloc(resultsize);
-		EOH_flatten_into(eoh, result, resultsize);
+		result = toast_EOH_datum(attr);
 	}
 	else
 	{
@@ -158,12 +150,7 @@ detoast_attr(struct varlena *attr)
 	}
 	else if (VARATT_IS_EXTERNAL_EXPANDED(attr))
 	{
-		/*
-		 * This is an expanded-object pointer --- get flat format
-		 */
-		attr = detoast_external_attr(attr);
-		/* flatteners are not allowed to produce compressed/short output */
-		Assert(!VARATT_IS_EXTENDED(attr));
+		attr = toast_EOH_datum(attr);
 	}
 	else if (VARATT_IS_COMPRESSED(attr))
 	{
@@ -279,7 +266,7 @@ detoast_attr_slice(struct varlena *attr,
 	else if (VARATT_IS_EXTERNAL_EXPANDED(attr))
 	{
 		/* pass it off to detoast_external_attr to flatten */
-		preslice = detoast_external_attr(attr);
+		preslice = toast_EOH_datum(attr);
 	}
 	else
 		preslice = attr;
@@ -491,7 +478,6 @@ toast_decompress_datum(struct varlena *attr)
 	}
 }
 
-
 /* ----------
  * toast_decompress_datum_slice -
  *
@@ -534,6 +520,32 @@ toast_decompress_datum_slice(struct varlena *attr, int32 slicelength)
 	}
 }
 
+
+/* ----------
+ * toast_EOH_datum -
+ *
+ *	Reconstruct a non-extended varlena form from a EOP version of a
+ *  varlena datum.
+ */
+static struct varlena *
+toast_EOH_datum(struct varlena *attr)
+{
+	/*
+	 * This is an expanded-object pointer --- get flat format
+	 */
+	ExpandedObjectHeader *eoh;
+	Size		resultsize;
+	struct varlena *result;
+
+	Assert(VARATT_IS_EXTERNAL_EXPANDED(attr));
+	eoh = DatumGetEOHP(PointerGetDatum(attr));
+	resultsize = EOH_get_flat_size(eoh);
+	result = (struct varlena *) palloc(resultsize);
+	EOH_flatten_into(eoh, (void *) result, resultsize);
+	Assert(!VARATT_IS_EXTENDED(result));
+	return result;
+}
+
 /* ----------
  * toast_raw_datum_size -
  *
-- 
2.45.1