Concurrency and transactions for the nzload command

You can run multiple nzload commands in parallel to add records to the same or different tables. While loading, you can run concurrent queries, inserts, updates, and deletes against committed records in the target tables.

The nzload command conducts all insertions into the target table within a single transaction. The nzload command commits the transaction at the end of the job if the command does not detect any unrecoverable errors. Only after the nzload command commits the transaction are the newly loaded records visible to other queries. If a load error occurs while multiple concurrent loads are running, only the load with the error is not completed.

While the nzload command is running, it sends records to the SPUs along with the current transaction ID. When an SPU receives new records, it immediately allocates resources and writes the records to the database or the table on the disk. If the nzload command cannot commit the transaction, these storage resources remain allocated. To free up this disk space, use the nzreclaim command against the specific table or database. For more information about the nzreclaim command, see the IBM® Netezza® System Administrator’s Guide.

If you cancel an nzload job, the nzload command does not commit the transaction.