1 files changed, 50 insertions, 0 deletions
diff --git a/django/db/backends/postgresql/compiler.py b/django/db/backends/postgresql/compiler.py
new file mode 100644
index 0000000000..2394d90f55
--- /dev/null
+++ b/django/db/backends/postgresql/compiler.py
@@ -0,0 +1,50 @@
+from django.db.models.sql.compiler import (
+    SQLAggregateCompiler,
+    SQLCompiler,
+    SQLDeleteCompiler,
+)
+from django.db.models.sql.compiler import SQLInsertCompiler as BaseSQLInsertCompiler
+from django.db.models.sql.compiler import SQLUpdateCompiler
+
+__all__ = [
+    "SQLAggregateCompiler",
+    "SQLCompiler",
+    "SQLDeleteCompiler",
+    "SQLInsertCompiler",
+    "SQLUpdateCompiler",
+]
+
+
+class InsertUnnest(list):
+    """
+    Sentinel value to signal DatabaseOperations.bulk_insert_sql() that the
+    UNNEST strategy should be used for the bulk insert.
+    """
+
+    def __str__(self):
+        return "UNNEST(%s)" % ", ".join(self)
+
+
+class SQLInsertCompiler(BaseSQLInsertCompiler):
+    def assemble_as_sql(self, fields, value_rows):
+        # Specialize bulk-insertion of literal non-array values through
+        # UNNEST to reduce the time spent planning the query.
+        if (
+            # The optimization is not worth doing if there is a single
+            # row as it will result in the same number of placeholders.
+            len(value_rows) <= 1
+            # Lack of fields denote the usage of the DEFAULT keyword
+            # for the insertion of empty rows.
+            or any(field is None for field in fields)
+            # Compilable cannot be combined in an array of literal values.
+            or any(any(hasattr(value, "as_sql") for value in row) for row in value_rows)
+        ):
+            return super().assemble_as_sql(fields, value_rows)
+        db_types = [field.db_type(self.connection) for field in fields]
+        # Abort if any of the fields are arrays as UNNEST indiscriminately
+        # flatten them instead of reducing their nesting by one.
+        if any(db_type.endswith("[]") for db_type in db_types):
+            return super().assemble_as_sql(fields, value_rows)
+        return InsertUnnest(["(%%s)::%s[]" % db_type for db_type in db_types]), [
+            list(map(list, zip(*value_rows)))
+        ]