Snapshot Transactions

At this moment, Exasol supports only one transaction isolation level: SERIALIZABLE.

This is good for data consistency, but it increases the probability of transactional conflicts. For more information, see:

• Transaction System

• WAIT FOR COMMIT on SELECT statement

The most common locking problem is related to metadata selects from system views (tables, column, object sizes, etc.). JDBC and ODBC drivers provide special non-blocking calls for common metadata requests: getTables(), getColumns(). But there are no such calls for WebSocket drivers.

The only way to access metadata in a non-blocking manner with PyExasol, is an internal feature called “Snapshot Transactions”. For information, see: * Transaction Management * Snapshot mode

Recommended Usage Pattern

If you want to read metadata without locks, and if strict transaction integrity is not an issue, please do the following:

1. Open new connection with option snapshot_transactions=True. Use this connection to read metadata from system views only.

2. Open another connection in normal mode and use it for everything else.

Please see c08_snapshot_transactions.py for a common locking scenario avoided by this feature.