Stale data

A side-effect of cursors is stale data. Stale data occurs when records have been changed in a table, but the corresponding records in client buffers have not been updated to reflect the changes. The following scenario illustrates how stale data occurs.

• Client A reads a record from a table. In this process, 25 records (the default block size) are copied to the client buffer.
• Client B reads and makes changes to a record from the same table as client A. The record that was changed happens to be one that was read into client A’s client buffer.
• If client A accesses the record that client B changed, it will read the record from the client buffer. This record has become stale, because the old record in the client buffer will be used, not the updated record in the table.

You won’t be able to eliminate stale data, but you can reduce the chances of it occurring. One solution is to reduce the cursor block size. By storing fewer records in the client buffer, you will reduce the number that could become stale. You can also use cursor refreshing, described in the next section, to help reduce the occurrence of stale data.

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