MDEV-23072 Diskspace not reused for Blob in data file

- This issue is caused by commit a4948da.
Purge doesn't free the externally stored page associated with the
last record of the root page. In that case, purge thread does empty
the root page and leads to more orphaned blob page in the tablespace.
Purge thread should free the blob even for the last record of the
root page.

Reviewed-by: Marko Mäkelä

storage/innobase/btr/btr0cur.cc

@@ -5469,7 +5469,6 @@ btr_cur_optimistic_delete_func(
 	mem_heap_t*	heap		= NULL;
 	rec_offs	offsets_[REC_OFFS_NORMAL_SIZE];
 	rec_offs*	offsets		= offsets_;
-	ibool		no_compress_needed;
 	rec_offs_init(offsets_);
 
 	ut_ad(flags == 0 || flags == BTR_CREATE_FLAG);
@@ -5490,6 +5489,20 @@ btr_cur_optimistic_delete_func(
 
 	rec = btr_cur_get_rec(cursor);
 
+	offsets = rec_get_offsets(rec, cursor->index, offsets, true,
+				  ULINT_UNDEFINED, &heap);
+
+	const ibool no_compress_needed = !rec_offs_any_extern(offsets)
+		&& btr_cur_can_delete_without_compress(
+			cursor, rec_offs_size(offsets), mtr);
+
+	if (!no_compress_needed) {
+		/* prefetch siblings of the leaf for the pessimistic
+		operation. */
+		btr_cur_prefetch_siblings(block);
+		goto func_exit;
+	}
+
 	if (UNIV_UNLIKELY(block->page.id.page_no() == cursor->index->page
 			  && page_get_n_recs(block->frame) == 1
 			  + (cursor->index->is_instant()
@@ -5528,18 +5541,10 @@ btr_cur_optimistic_delete_func(
 			index->remove_instant();
 		}
 
-		return true;
+		goto func_exit;
 	}
 
-	offsets = rec_get_offsets(rec, cursor->index, offsets, true,
-				  ULINT_UNDEFINED, &heap);
-
-	no_compress_needed = !rec_offs_any_extern(offsets)
-		&& btr_cur_can_delete_without_compress(
-			cursor, rec_offs_size(offsets), mtr);
-
-	if (no_compress_needed) {
-
+	{
 		page_t*		page	= buf_block_get_frame(block);
 		page_zip_des_t*	page_zip= buf_block_get_page_zip(block);
 
@@ -5599,10 +5604,6 @@ btr_cur_optimistic_delete_func(
 				ibuf_update_free_bits_low(block, max_ins, mtr);
 			}
 		}
-	} else {
-		/* prefetch siblings of the leaf for the pessimistic
-		operation. */
-		btr_cur_prefetch_siblings(block);
 	}
 
 func_exit: