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A new transaction starts with the first LOAD command or DML statement entered in a new Hyperstage session. A new transaction also starts after each COMMIT or ROLLBACK command.

• To enable the use of COMMIT and ROLLBACK commands in Hyperstage, you must disable AUTOCOMMIT. Enter the following command:

  mysql> set autocommit=0;

You can disable AUTOCOMMIT by setting the parameter to 0 (zero) and enable AUTOCOMMIT by setting the parameter to 1. If AUTOCOMMIT is set to 1, then when a LOAD is completed, the transaction is automatically committed.

• To commit the current transaction, enter the following command:

  mysql> commit;

• If you have not yet committed a LOAD DATA INFILE transaction, you can rollback the transaction. This will restore the import tables to the state that existed before the current transaction. Enter the following command:

  mysql> rollback;

Using COMMIT and ROLLBACK makes it possible to check the load within the same session before committing the data, as the loaded data is available (viewable) to the load session. For instance, you could check something about the data (number of records load) before committing.

After importing data using the LOAD DATA INFILE command, the status of the import and the number of affected rows is shown. All uncommitted rows, including those from previous imports, are shown. Therefore, the number of affected rows may be greater than the number of rows in the file you just imported.

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While a write operation is being performed on a table, the following occurs:

• Queries to the table are executed against the state of the database before the write operation began. Once the current LOAD or INSERT/UPDATE/DELETE is complete and the operation is committed, then subsequent queries execute against the new state of the database.
• Until the current write operation is committed, all subsequent write commands to the table are queued. They will wait for the write lock to be released before proceeding in the order they were received.

While a read query is being executed on a table, the following occurs:

• All subsequent queries run concurrently with the current query.
• A subsequent LOAD or INSERT/UPDATE/DELETE command will run concurrently with the current queries. Further write operations with queue (as described above).

In general, Hyperstage uses table level locking where only one write operation (INSERT, UPDATE, DELETE, or LOAD) can execute at one time.

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If AUTOCOMMIT is disabled and the Hyperstage server is terminated during an import session, the following occurs:

• Hyperstage does not store the rows that were loaded during the failed import operation.
• The input file and the database files are not harmed. To load data from the input file, repeat the LOAD operation.

If AUTOCOMMIT is disabled and the Hyperstage server is terminated after an import session is completed successfully but is not committed, the following occurs:

• The transaction is rolled back and the imported data is lost when the server restarts.
• The input file and the database files are not harmed by the failed import operation (the database is unaffected, as if the import session did not occur). To reimport the data, repeat the LOAD operation.

If the Hyperstage server is terminated during an export operation to a disk file, the following occurs:

• A non-empty file is saved on disk. However, the last row in the saved file is inconsistent.
• The database files are not harmed by the failed export operation. To export the data, repeat the export operation.

If Hyperstage tries to import data from a file created during a failed export session, the following occurs:

• No data is inserted because the input file consists of corrupted table rows. No new records are added to the database files, so no harm is done.