fix: Support PostgreSQL 12 in get_top_queries

src/postgres_mcp/top_queries/top_queries_calc.py

@@ -139,14 +139,21 @@ async def get_top_resource_queries(self, frac_threshold: float = 0.05) -> str:
             logger.debug(f"PostgreSQL version: {pg_version}")
 
             # Column names changed in PostgreSQL 13
+            # Also, wal_bytes was added in PostgreSQL 13
             if pg_version >= 13:
                 # PostgreSQL 13 and newer
                 total_time_col = "total_exec_time"
                 mean_time_col = "mean_exec_time"
+                stddev_time_col = "stddev_exec_time"
+                wal_bytes_col = "wal_bytes"
+                wal_bytes_frac = "wal_bytes / NULLIF(SUM(wal_bytes) OVER (), 0) AS total_wal_bytes_frac"
             else:
                 # PostgreSQL 12 and older
                 total_time_col = "total_time"
                 mean_time_col = "mean_time"
+                stddev_time_col = "stddev_time"
+                wal_bytes_col = "0 AS wal_bytes"  # Column doesn't exist in PG12
+                wal_bytes_frac = "0 AS total_wal_bytes_frac"
 
             query = cast(
                 LiteralString,
@@ -156,18 +163,23 @@ async def get_top_resource_queries(self, frac_threshold: float = 0.05) -> str:
                         query,
                         calls,
                         rows,
-                        {total_time_col} total_exec_time,
-                        {mean_time_col} mean_exec_time,
-                        stddev_exec_time,
+                        {total_time_col} AS total_exec_time,
+                        {mean_time_col} AS mean_exec_time,
+                        {stddev_time_col} AS stddev_exec_time,
                         shared_blks_hit,
                         shared_blks_read,
                         shared_blks_dirtied,
-                        wal_bytes,
-                        total_exec_time / SUM(total_exec_time) OVER () AS total_exec_time_frac,
-                        (shared_blks_hit + shared_blks_read) / SUM(shared_blks_hit + shared_blks_read) OVER () AS shared_blks_accessed_frac,
-                        shared_blks_read / SUM(shared_blks_read) OVER () AS shared_blks_read_frac,
-                        shared_blks_dirtied / SUM(shared_blks_dirtied) OVER () AS shared_blks_dirtied_frac,
-                        wal_bytes / SUM(wal_bytes) OVER () AS total_wal_bytes_frac
+                        {wal_bytes_col},
+                        {total_time_col} / NULLIF(SUM({total_time_col}) OVER (), 0)
+                            AS total_exec_time_frac,
+                        (shared_blks_hit + shared_blks_read)
+                            / NULLIF(SUM(shared_blks_hit + shared_blks_read) OVER (), 0)
+                            AS shared_blks_accessed_frac,
+                        shared_blks_read / NULLIF(SUM(shared_blks_read) OVER (), 0)
+                            AS shared_blks_read_frac,
+                        shared_blks_dirtied / NULLIF(SUM(shared_blks_dirtied) OVER (), 0)
+                            AS shared_blks_dirtied_frac,
+                        {wal_bytes_frac}
                     FROM pg_stat_statements
                 )
                 SELECT

tests/conftest.py

@@ -17,7 +17,7 @@ def event_loop_policy():
     return asyncio.DefaultEventLoopPolicy()
 
 
-@pytest.fixture(scope="class", params=["postgres:15", "postgres:16"])
+@pytest.fixture(scope="class", params=["postgres:12", "postgres:15", "postgres:16"])
 def test_postgres_connection_string(request) -> Generator[tuple[str, str], None, None]:
     yield from create_postgres_container(request.param)
 

tests/unit/top_queries/test_top_queries_calc.py

@@ -212,3 +212,43 @@ async def test_error_handling(mock_pg13_driver, mock_extension_installed):
 
     # Check that the error is properly reported
     assert "Error getting slow queries: Database error" in result
+
+
+@pytest.mark.asyncio
+async def test_resource_queries_pg12(mock_pg12_driver, mock_extension_installed):
+    """Test resource queries on PostgreSQL 12 uses correct column names (stddev_time, no wal_bytes)."""
+    # Create the TopQueriesCalc instance with the mock driver
+    calc = TopQueriesCalc(sql_driver=mock_pg12_driver)
+
+    # Get resource queries
+    _result = await calc.get_top_resource_queries(frac_threshold=0.05)
+
+    # Get the executed query from the mock
+    call_args = str(mock_pg12_driver.execute_query.call_args)
+
+    # Verify PG12 column names are used (aliased to consistent output names)
+    assert "stddev_time AS stddev_exec_time" in call_args, "Should use stddev_time aliased for PG12"
+    assert "total_time AS total_exec_time" in call_args, "Should use total_time aliased for PG12"
+    assert "mean_time AS mean_exec_time" in call_args, "Should use mean_time aliased for PG12"
+    # wal_bytes should be replaced with 0 for PG12
+    assert "0 AS wal_bytes" in call_args, "Should use 0 AS wal_bytes for PG12"
+
+
+@pytest.mark.asyncio
+async def test_resource_queries_pg13(mock_pg13_driver, mock_extension_installed):
+    """Test resource queries on PostgreSQL 13 uses correct column names (stddev_exec_time, wal_bytes)."""
+    # Create the TopQueriesCalc instance with the mock driver
+    calc = TopQueriesCalc(sql_driver=mock_pg13_driver)
+
+    # Get resource queries
+    _result = await calc.get_top_resource_queries(frac_threshold=0.05)
+
+    # Get the executed query from the mock
+    call_args = str(mock_pg13_driver.execute_query.call_args)
+
+    # Verify PG13 column names are used
+    assert "stddev_exec_time" in call_args, "Should use stddev_exec_time for PG13"
+    assert "total_exec_time" in call_args, "Should use total_exec_time for PG13"
+    assert "mean_exec_time" in call_args, "Should use mean_exec_time for PG13"
+    # wal_bytes should be the actual column for PG13
+    assert "wal_bytes" in call_args, "Should use wal_bytes column for PG13"