Support Cursor.rowcount and close finished queries #528
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With current Impala server rowcount support needs DMLs to be closed with CloseImpalaOperation() as there is no simpler way to get the number of modifed rows. See https://issues.apache.org/jira/browse/IMPALA-12647 for alternatives. This change adds option close_finished_queries for cursors with default True. Setting it to False brings back the old behavior. If queries are closed after finishing queries, calling get_log RPC is no longer possible. If close_finished_queries is true then the logs are fetched and stored before closing to query to be able to return the saved results with get_log. Generally get_log shouldn't be a too expensive RPC. Another potential side-effect is that get_profile may fail as Impala can discard the runtime profile after the query is closed (see Impala flag query_log_size). Despite the above side effects closing the queries seems a better default behavior as it helps avoiding queries hanging in the "waiting to be closed" state and provides reliable rowcount. This is also consistent with the way impala-shell works. Testing: - rowcount already had good coverage in DBAPI2 compliance tests (e.g. test_mixedfetch) - new tests were added for some missing rowcount cases and for getting warning/error log for closed queries
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impala/hiveserver2.py
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| queries with results set: all rows are returned with fetch | ||
| DDL/DML: execution is finished | ||
| If False, then the query will be only closed when the cursor is closed | ||
| or when its destructor is called. Property rowcount will not be available |
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Minor thought: When a cursor is re-used for multiple query executions, it looks like it calls _reset_state() when each new query is executed. _reset_state() calls CloseOperation on any existing operation. Should we change the "If False" case to say that executing a new query closes the old query?
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I'm not sure what our process is, should we file an issue on github for this? |
There is already an issue about rowcount: #302 |
joemcdonnell
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Jan 29, 2024
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With current Impala server rowcount support needs DMLs to be closed with CloseImpalaOperation() as there is no simpler way to get the number of modifed rows.
See https://issues.apache.org/jira/browse/IMPALA-12647 for alternatives.
This change adds option close_finished_queries for cursors with default True. Setting it to False brings back the old behavior.
If queries are closed after finishing queries, calling get_log RPC is no longer possible. If close_finished_queries is true then the logs are fetched and stored before closing to query to be able to return the saved results with get_log. Generally get_log shouldn't be a too expensive RPC.
Another potential side-effect is that get_profile may fail as Impala can discard the runtime profile after the query is closed (see Impala flag query_log_size).
Despite the above side effects closing the queries seems a better default behavior as it helps avoiding queries hanging in the "waiting to be closed" state and provides reliable rowcount. This is also consistent with the way impala-shell works.
Testing: