Sybase IQ has special features that ensure data consistency in a data warehouse environment.
In a data warehouse environment, many users need to read from the database, but only the DBA needs to update it. However, there is often a need to make updates while other users continue to request and receive query results. Sybase IQ keeps track of database changes using table-level snapshot versioning. It keeps a record of what the table looks like when a user begins a write transaction.
Sybase IQ allows multiple readers, but only one writer to a table. To test data consistency, you will connect as two different users and try to write to a table from both connections at the same time. One statement will be rolled back and will receive an error message while the other commits.
After each transaction commits, Sybase IQ writes updated data pages to disk. This approach is ideal for the data warehouse, where a single application may write millions of rows of data. A checkpoint is a point in a transaction when the database writes information to disk. Most OLTP databases write data to disk at checkpoints. Sybase IQ does not wait for a checkpoint to write physical data. Sybase IQ uses checkpoints to write certain information to disk for internal tracking, which is used if you need to recover your database. While you may set explicit checkpoints, most Sybase IQ checkpoints occur automatically.