add comments

src/server/pegasus_server_impl.cpp

@@ -1197,10 +1197,10 @@ void pegasus_server_impl::on_get_scanner(const ::dsn::apps::get_scanner_request
             start_inclusive = true;
             // Now 'start' is generated by 'request.hash_key_filter_pattern', it may be not a real
             // hashkey, we should not seek this prefix by prefix bloom filter. However, it only
-            // happend when do full scan (scanners got by get_unordered_scanners), in which case the
+            // happen when do full scan (scanners got by get_unordered_scanners), in which case the
             // following flags has been updated.
-            assert(!_db_opts.prefix_extractor || rd_opts.total_order_seek);
-            assert(!_db_opts.prefix_extractor || !rd_opts.prefix_same_as_start);
+            dassert(!_db_opts.prefix_extractor || rd_opts.total_order_seek);
+            dassert(!_db_opts.prefix_extractor || !rd_opts.prefix_same_as_start);
         }
     }
 

src/server/test/hashkey_transform_test.cpp

@@ -9,7 +9,11 @@
 
 #include "base/pegasus_key_schema.h"
 
-// User define SliceTransform must obey the 4 rules of ColumnFamilyOptions.prefix_extractor
+// User define SliceTransform must obey the 4 rules of ColumnFamilyOptions.prefix_extractor:
+// 1) key.starts_with(prefix(key))
+// 2) Compare(prefix(key), key) <= 0.
+// 3) If Compare(k1, k2) <= 0, then Compare(prefix(k1), prefix(k2)) <= 0
+// 4) prefix(prefix(key)) == prefix(key)
 TEST(HashkeyTransformTest, Basic)
 {
     pegasus::server::HashkeyTransform prefix_extractor;