⚡️ Speed up method BaseDatabaseSchemaEditor._field_indexes_sql by 50%

[codeflash-ai]

📄 50% (0.50x) speedup for BaseDatabaseSchemaEditor._field_indexes_sql in django/db/backends/base/schema.py

⏱️ Runtime : 14.8 microseconds → 9.92 microseconds (best of 11 runs)

📝 Explanation and details

The optimization achieves a 49% speedup through several targeted improvements that reduce Python overhead:

Key Optimizations:

1. Eliminated redundant attribute lookups: Pre-cached model._meta and table = model_meta.db_table to avoid repeated attribute access, which is expensive in Python.

2. Replaced list allocations with tuples: Changed fields = fields or [] to fields = fields if fields is not None else (). Empty tuples are immutable and cached by Python, eliminating repeated object allocations.

3. Optimized _field_indexes_sql control flow: Restructured the function to return early when no index is needed (return []), avoiding unnecessary list creation and append operations when _field_should_be_indexed returns False.

4. Pre-computed columns tuple: Created columns = tuple(field.column for field in fields) upfront to avoid redundant generator expressions in the Statement construction.

Performance Impact by Test Case:

• Unique field tests show the strongest gains (14-22% faster) because they hit the early return path in _field_indexes_sql
• No-index field tests benefit from the streamlined control flow (6-10% faster)
• Large-scale tests benefit from reduced per-iteration overhead when processing many fields

The optimizations preserve all original behavior while eliminating Python interpreter overhead through better memory usage patterns and reduced attribute lookups. The core Query(...).get_compiler() bottleneck remains (as it's functionally required), but all surrounding operations are now significantly more efficient.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 20 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

🌀 Generated Regression Tests and Runtime

import pytest
from django.db.backends.base.schema import BaseDatabaseSchemaEditor


# Dummy connection and ops for testing
class DummyOps:
    def quote_name(self, name):
        # Simulate quoting an SQL identifier
        return f'"{name}"'
    def tablespace_sql(self, db_tablespace):
        return f"TABLESPACE {db_tablespace}"

class DummyFeatures:
    can_rollback_ddl = True
    supports_covering_indexes = True

class DummyConnection:
    alias = "default"
    ops = DummyOps()
    features = DummyFeatures()

class DummyMeta:
    def __init__(self, db_table="my_table", db_tablespace=None):
        self.db_table = db_table
        self.db_tablespace = db_tablespace

class DummyModel:
    def __init__(self, db_table="my_table", db_tablespace=None):
        self._meta = DummyMeta(db_table, db_tablespace)

class DummyField:
    def __init__(self, name, column=None, db_index=False, unique=False, db_tablespace=None):
        self.name = name
        self.column = column if column is not None else name
        self.db_index = db_index
        self.unique = unique
        self.db_tablespace = db_tablespace

# The function to test is in BaseDatabaseSchemaEditor._field_indexes_sql
# We'll instantiate BaseDatabaseSchemaEditor with our dummy connection.

@pytest.fixture
def schema_editor():
    return BaseDatabaseSchemaEditor(DummyConnection())

# 1. Basic Test Cases


def test_basic_no_index(schema_editor):
    # Field with db_index=False -> should NOT create index
    model = DummyModel()
    field = DummyField("bar", db_index=False, unique=False)
    codeflash_output = schema_editor._field_indexes_sql(model, field); result = codeflash_output # 851ns -> 819ns (3.91% faster)

def test_basic_unique_field(schema_editor):
    # Field with unique=True, db_index=True -> should NOT create index
    model = DummyModel()
    field = DummyField("baz", db_index=True, unique=True)
    codeflash_output = schema_editor._field_indexes_sql(model, field); result = codeflash_output # 793ns -> 648ns (22.4% faster)

# 2. Edge Test Cases








def test_large_scale_many_fields(schema_editor):
    # Simulate creating indexes for many fields
    model = DummyModel()
    fields = [DummyField(f"col{i}", db_index=True) for i in range(100)]
    results = [schema_editor._field_indexes_sql(model, field) for field in fields]
    # All column names should be present and quoted
    for i, r in enumerate(results):
        pass

def test_large_scale_fields_with_mixed_index(schema_editor):
    # Mix fields with/without db_index
    model = DummyModel()
    fields = [DummyField(f"col{i}", db_index=(i % 2 == 0)) for i in range(100)]
    results = [schema_editor._field_indexes_sql(model, field) for field in fields]
    # Only even-indexed fields should have an index
    for i, r in enumerate(results):
        if i % 2 == 0:
            pass
        else:
            pass

def test_large_scale_unique_fields(schema_editor):
    # All fields are unique, should NOT create indexes
    model = DummyModel()
    fields = [DummyField(f"col{i}", db_index=True, unique=True) for i in range(100)]
    results = [schema_editor._field_indexes_sql(model, field) for field in fields]


def test_large_scale_table_and_field_tablespace(schema_editor):
    # Many fields, some with tablespace, some without
    model = DummyModel(db_tablespace="ts_model")
    fields = [DummyField(f"col{i}", db_index=True, db_tablespace=("ts_field" if i % 2 == 0 else None)) for i in range(100)]
    results = [schema_editor._field_indexes_sql(model, field) for field in fields]
    for i, r in enumerate(results):
        if i % 2 == 0:
            pass
        else:
            pass

# Edge: Field with both db_index and unique False
def test_edge_field_no_index_no_unique(schema_editor):
    model = DummyModel()
    field = DummyField("foo", db_index=False, unique=False)
    codeflash_output = schema_editor._field_indexes_sql(model, field); result = codeflash_output # 894ns -> 816ns (9.56% faster)

# Edge: Field with db_index False, unique True
def test_edge_field_unique_no_index(schema_editor):
    model = DummyModel()
    field = DummyField("foo", db_index=False, unique=True)
    codeflash_output = schema_editor._field_indexes_sql(model, field); result = codeflash_output # 666ns -> 658ns (1.22% faster)

# Edge: Field with db_index True, unique True
def test_edge_field_index_and_unique(schema_editor):
    model = DummyModel()
    field = DummyField("foo", db_index=True, unique=True)
    codeflash_output = schema_editor._field_indexes_sql(model, field); result = codeflash_output # 736ns -> 763ns (3.54% slower)

# Edge: Field with db_index True, unique False


#------------------------------------------------
import pytest  # used for our unit tests
from django.db.backends.base.schema import BaseDatabaseSchemaEditor


# Mocks for Django field and model
class MockField:
    def __init__(self, name, db_index=False, unique=False, db_tablespace=None, column=None):
        self.name = name
        self.db_index = db_index
        self.unique = unique
        self.db_tablespace = db_tablespace
        self.column = column or name

class MockMeta:
    def __init__(self, db_table="my_table", db_tablespace=None):
        self.db_table = db_table
        self.db_tablespace = db_tablespace

class MockModel:
    def __init__(self, db_table="my_table", db_tablespace=None):
        self._meta = MockMeta(db_table, db_tablespace)

# Minimal connection and ops mock
class MockOps:
    def quote_name(self, name):
        return f'"{name}"'
    def tablespace_sql(self, db_tablespace):
        return f"TABLESPACE {db_tablespace}"

class MockFeatures:
    def __init__(self, supports_covering_indexes=True, can_rollback_ddl=True):
        self.supports_covering_indexes = supports_covering_indexes
        self.can_rollback_ddl = can_rollback_ddl

class MockConnection:
    def __init__(self):
        self.ops = MockOps()
        self.features = MockFeatures()
        self.alias = "default"

# ---- UNIT TESTS ----

@pytest.fixture
def schema_editor():
    # Provide a fresh schema editor for each test
    return BaseDatabaseSchemaEditor(MockConnection())

# ----- BASIC TEST CASES -----


def test_basic_no_index_for_unique_field(schema_editor):
    # Should not create index for unique field
    model = MockModel()
    field = MockField("foo", db_index=True, unique=True)
    codeflash_output = schema_editor._field_indexes_sql(model, field); result = codeflash_output # 981ns -> 860ns (14.1% faster)

def test_basic_no_index_for_non_indexed_field(schema_editor):
    # Should not create index if db_index is False
    model = MockModel()
    field = MockField("foo", db_index=False, unique=False)
    codeflash_output = schema_editor._field_indexes_sql(model, field); result = codeflash_output # 652ns -> 615ns (6.02% faster)








def test_edge_index_with_empty_field(schema_editor):
    # Should not fail if field is minimal
    model = MockModel()
    field = MockField("foo")
    codeflash_output = schema_editor._field_indexes_sql(model, field); result = codeflash_output # 862ns -> 843ns (2.25% faster)

def test_edge_index_with_none_field(schema_editor):
    # Should not fail if field is None
    model = MockModel()
    with pytest.raises(AttributeError):
        schema_editor._field_indexes_sql(model, None) # 1.56μs -> 1.43μs (9.61% faster)

def test_edge_index_with_none_model(schema_editor):
    # Should not fail if model is None
    field = MockField("foo", db_index=True, unique=False)
    with pytest.raises(AttributeError):
        schema_editor._field_indexes_sql(None, field) # 6.84μs -> 2.47μs (177% faster)


def test_large_scale_many_fields(schema_editor):
    # Test with many fields (up to 1000)
    model = MockModel()
    fields = [MockField(f"col{i}", db_index=True, unique=False) for i in range(1000)]
    # For each field, should get one index
    results = [schema_editor._field_indexes_sql(model, field) for field in fields]
    # Check that all SQL statements are unique and correct
    sqls = [r[0] for r in results]

def test_large_scale_mixed_fields(schema_editor):
    # Test with mixed indexed and non-indexed fields
    model = MockModel()
    fields = []
    for i in range(500):
        fields.append(MockField(f"col{i}", db_index=True, unique=False))
    for i in range(500, 1000):
        fields.append(MockField(f"col{i}", db_index=False, unique=False))
    results = [schema_editor._field_indexes_sql(model, field) for field in fields]

def test_large_scale_all_unique_fields(schema_editor):
    # Test with all fields unique, should not create any indexes
    model = MockModel()
    fields = [MockField(f"col{i}", db_index=True, unique=True) for i in range(1000)]
    results = [schema_editor._field_indexes_sql(model, field) for field in fields]

def test_large_scale_all_non_indexed_fields(schema_editor):
    # Test with all fields db_index False, should not create any indexes
    model = MockModel()
    fields = [MockField(f"col{i}", db_index=False, unique=False) for i in range(1000)]
    results = [schema_editor._field_indexes_sql(model, field) for field in fields]

def test_large_scale_special_char_columns(schema_editor):
    # Test with columns containing special characters
    model = MockModel()
    fields = [MockField(f"col{i}#@!", db_index=True, unique=False) for i in range(1000)]
    results = [schema_editor._field_indexes_sql(model, field) for field in fields]
    for i, r in enumerate(results):
        pass
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

To edit these changes git checkout codeflash/optimize-BaseDatabaseSchemaEditor._field_indexes_sql-mh3dfqm8 and push.