FIX: Fix for isolation level for in-built connection pool

[subrata-ms]

AB#40573

GitHub Issue: #337

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Summary

This pull request addresses a critical issue in connection pooling for the mssql_python library by ensuring that the transaction isolation level is properly reset when a pooled connection is reused. Previously, the isolation level could leak between usages, potentially causing unexpected behavior. The changes include an explicit reset of the isolation level in the connection reset logic and a new test to verify this behavior.

Bug fix for connection pooling session state:

• Explicitly reset the transaction isolation level to READ COMMITTED in the Connection::reset() method to prevent isolation level settings from leaking between pooled connection usages. This addresses the limitation of SQL_ATTR_RESET_CONNECTION, which does not reset the isolation level. (mssql_python/pybind/connection/connection.cpp)

Testing improvements:

• Added a new test test_connection_pooling_isolation_level_reset in tests/test_009_pooling.py to verify that the isolation level is reset to the default when a connection is reused from the pool, preventing session state leakage.
• Imported the mssql_python module in tests/test_009_pooling.py to support new test functionality.

[Copilot]

Pull request overview

This pull request fixes a critical bug in connection pooling where the transaction isolation level was not being reset when connections were returned to and reused from the pool. The fix ensures that READ COMMITTED (the SQL Server default) is explicitly set during connection reset, preventing session state leakage between pooled connection usages.

Key changes:

• Added explicit transaction isolation level reset to READ COMMITTED in the Connection::reset() method after SQL_ATTR_RESET_CONNECTION is called
• Added comprehensive test to verify that isolation level is properly reset when connections are reused from the pool

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
mssql_python/pybind/connection/connection.cpp	Adds explicit reset of transaction isolation level to SQL_TXN_READ_COMMITTED in the Connection::reset() method to prevent isolation level leakage between pooled connection usages
tests/test_009_pooling.py	Imports mssql_python module and adds test_connection_pooling_isolation_level_reset test to verify isolation level is reset to default when connections are reused from the pool

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[github-actions]

📊 Code Coverage Report

🔥 Diff Coverage 50%

🎯 Overall Coverage 75%

📈 Total Lines Covered: 5094 out of 6757 📁 Project: mssql-python

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Diff Coverage

Diff: main...HEAD, staged and unstaged changes

• mssql_python/pybind/connection/connection.cpp (50.0%): Missing lines 319-322

Summary

• Total: 8 lines
• Missing: 4 lines
• Coverage: 50%

mssql_python/pybind/connection/connection.cpp

Lines 315-326

  315     LOG("Resetting transaction isolation level to READ COMMITTED");
  316     ret = SQLSetConnectAttr_ptr(_dbcHandle->get(), SQL_ATTR_TXN_ISOLATION,
  317                                 (SQLPOINTER)SQL_TXN_READ_COMMITTED, SQL_IS_INTEGER);
  318     if (!SQL_SUCCEEDED(ret)) {
! 319         LOG("Failed to reset transaction isolation level (ret=%d). Marking as dead.", ret);
! 320         disconnect();
! 321         return false;
! 322     }
  323     
  324     updateLastUsed();
  325     return true;
  326 }

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📋 Files Needing Attention

📉 Files with overall lowest coverage (click to expand)

mssql_python.pybind.logger_bridge.cpp: 59.2%
mssql_python.row.py: 66.2%
mssql_python.pybind.ddbc_bindings.cpp: 67.1%
mssql_python.helpers.py: 67.5%
mssql_python.pybind.connection.connection.cpp: 73.6%
mssql_python.pybind.ddbc_bindings.h: 76.9%
mssql_python.ddbc_bindings.py: 79.6%
mssql_python.pybind.connection.connection_pool.cpp: 79.6%
mssql_python.connection.py: 82.5%
mssql_python.cursor.py: 83.8%

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[saurabh500]

Need verification for Txn Level altered with ALTER DATABASE

[saurabh500]

Provided some feedback. For its current scope the PR looks good.