Avoid executing no-op queries. (#16583)

If simple_{insert,upsert,update}_many_txn is called without any data
to modify then return instead of executing the query.

This matches the behavior of simple_{select,delete}_many_txn.

1 files changed, 23 insertions, 9 deletions

diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index abc7d8a5d2..792f2e7cdf 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -1117,7 +1117,7 @@ class DatabasePool:
         txn: LoggingTransaction,
         table: str,
         keys: Collection[str],
-        values: Iterable[Iterable[Any]],
+        values: Collection[Iterable[Any]],
     ) -> None:
         """Executes an INSERT query on the named table.
 
@@ -1130,6 +1130,9 @@ class DatabasePool:
             keys: list of column names
             values: for each row, a list of values in the same order as `keys`
         """
+        # If there's nothing to insert, then skip executing the query.
+        if not values:
+            return
 
         if isinstance(txn.database_engine, PostgresEngine):
             # We use `execute_values` as it can be a lot faster than `execute_batch`,
@@ -1455,7 +1458,7 @@ class DatabasePool:
         key_names: Collection[str],
         key_values: Collection[Iterable[Any]],
         value_names: Collection[str],
-        value_values: Iterable[Iterable[Any]],
+        value_values: Collection[Iterable[Any]],
     ) -> None:
         """
         Upsert, many times.
@@ -1468,6 +1471,19 @@ class DatabasePool:
             value_values: A list of each row's value column values.
                 Ignored if value_names is empty.
         """
+        # If there's nothing to upsert, then skip executing the query.
+        if not key_values:
+            return
+
+        # No value columns, therefore make a blank list so that the following
+        # zip() works correctly.
+        if not value_names:
+            value_values = [() for x in range(len(key_values))]
+        elif len(value_values) != len(key_values):
+            raise ValueError(
+                f"{len(key_values)} key rows and {len(value_values)} value rows: should be the same number."
+            )
+
         if table not in self._unsafe_to_upsert_tables:
             return self.simple_upsert_many_txn_native_upsert(
                 txn, table, key_names, key_values, value_names, value_values
@@ -1502,10 +1518,6 @@ class DatabasePool:
             value_values: A list of each row's value column values.
                 Ignored if value_names is empty.
         """
-        # No value columns, therefore make a blank list so that the following
-        # zip() works correctly.
-        if not value_names:
-            value_values = [() for x in range(len(key_values))]
 
         # Lock the table just once, to prevent it being done once per row.
         # Note that, according to Postgres' documentation, once obtained,
@@ -1543,10 +1555,7 @@ class DatabasePool:
         allnames.extend(value_names)
 
         if not value_names:
-            # No value columns, therefore make a blank list so that the
-            # following zip() works correctly.
             latter = "NOTHING"
-            value_values = [() for x in range(len(key_values))]
         else:
             latter = "UPDATE SET " + ", ".join(
                 k + "=EXCLUDED." + k for k in value_names
@@ -1910,6 +1919,7 @@ class DatabasePool:
         Returns:
             The results as a list of tuples.
         """
+        # If there's nothing to select, then skip executing the query.
         if not iterable:
             return []
 
@@ -2044,6 +2054,9 @@ class DatabasePool:
             raise ValueError(
                 f"{len(key_values)} key rows and {len(value_values)} value rows: should be the same number."
             )
+        # If there is nothing to update, then skip executing the query.
+        if not key_values:
+            return
 
         # List of tuples of (value values, then key values)
         # (This matches the order needed for the query)
@@ -2278,6 +2291,7 @@ class DatabasePool:
         Returns:
             Number rows deleted
         """
+        # If there's nothing to delete, then skip executing the query.
         if not values:
             return 0