#223: Made profile_exasol_query side-effect free. (#224)

Author: ahsimb

doc/changes/unreleased.md

@@ -1,5 +1,11 @@
 # Unreleased
 
+## Bug Fixes
+
+* #223: Fixed `profile_exasol_query` to be side-effect free: the tool now checks whether
+  session profiling is already enabled via `SYS.EXA_PARAMETERS` and skips the
+  `ALTER SESSION SET PROFILE` statements if it was already `ON`.
+
 ## Features
 
 * #217: Added `summarize_exasol_table` tool that returns per-column statistics

exasol/ai/mcp/server/tools/mcp_server.py

@@ -350,6 +350,15 @@ def _build_list_preprocessors_query() -> str:
     )
 
 
+def _build_profile_status_query() -> str:
+    return (
+        exp.select(exp.column("SESSION_VALUE"))
+        .from_(exp.Table(this=exp.Identifier(this="EXA_PARAMETERS"), db=_SYS))
+        .where(exp.column("PARAMETER_NAME").eq("PROFILE"))
+        .sql(dialect="exasol", identify=True)
+    )
+
+
 def _build_current_preprocessor_query() -> str:
     return (
         exp.select(exp.column("SESSION_VALUE"))
@@ -639,13 +648,17 @@ def profile_query(self, query: QueryArg) -> list[dict[str, Any]]:
             raise RuntimeError("Query profiling is disabled.")
         if not verify_query(query):
             raise ValueError("The query is invalid or not a SELECT statement.")
-        statements = [
-            "ALTER SESSION SET PROFILE = 'ON'",
-            query,
-            "FLUSH STATISTICS",
-            "ALTER SESSION SET PROFILE = 'OFF'",
-            _build_profile_select(query),
-        ]
+        profile_already_on = (
+            self.connection.execute_query(_build_profile_status_query()).fetchval()
+            == "ON"
+        )
+        statements: list[str] = []
+        if not profile_already_on:
+            statements.append("ALTER SESSION SET PROFILE = 'ON'")
+        statements.extend([query, "FLUSH STATISTICS"])
+        if not profile_already_on:
+            statements.append("ALTER SESSION SET PROFILE = 'OFF'")
+        statements.append(_build_profile_select(query))
         return self.connection.execute_query(statements, snapshot=False).fetchall()
 
     async def execute_write_query(self, query: QueryArg, ctx: Context) -> str | None:

test/unit/tools/test_mcp_server.py

@@ -12,6 +12,7 @@
     _build_list_preprocessors_query,
     _build_preview_query,
     _build_profile_select,
+    _build_profile_status_query,
     _build_set_preprocessor_query,
     _build_stats_query,
     _build_top_values_query,
@@ -387,6 +388,45 @@ def test_build_profile_select():
     assert sql == expected
 
 
+def test_build_profile_status_query():
+    sql = collapse_spaces(_build_profile_status_query())
+    expected = collapse_spaces("""
+        SELECT "SESSION_VALUE"
+        FROM "SYS"."EXA_PARAMETERS"
+        WHERE "PARAMETER_NAME" = 'PROFILE'
+    """)
+    assert sql == expected
+
+
+def _make_profile_server(profile_already_on: bool):
+    connection = MagicMock()
+    connection.execute_query.return_value.fetchval.return_value = (
+        "ON" if profile_already_on else "OFF"
+    )
+    connection.execute_query.return_value.fetchall.return_value = []
+    config = MagicMock()
+    config.enable_query_profiling = True
+    server = ExasolMCPServer(connection=connection, config=config)
+    return server, connection
+
+
+def test_profile_query_enables_and_disables_profiling_when_off():
+    server, connection = _make_profile_server(profile_already_on=False)
+    server.profile_query("SELECT 1")
+    calls = [str(c) for c in connection.execute_query.call_args_list]
+    statements = connection.execute_query.call_args_list[-1][0][0]
+    assert statements[0] == "ALTER SESSION SET PROFILE = 'ON'"
+    assert statements[-2] == "ALTER SESSION SET PROFILE = 'OFF'"
+
+
+def test_profile_query_skips_profile_toggle_when_already_on():
+    server, connection = _make_profile_server(profile_already_on=True)
+    server.profile_query("SELECT 1")
+    statements = connection.execute_query.call_args_list[-1][0][0]
+    assert "ALTER SESSION SET PROFILE = 'ON'" not in statements
+    assert "ALTER SESSION SET PROFILE = 'OFF'" not in statements
+
+
 def test_build_list_preprocessors_query():
     sql = collapse_spaces(_build_list_preprocessors_query())
     expected = collapse_spaces("""