ORA-08176: consistent read failure; rollback data not available

What does it mean?

While building a consistent read image, a query encountered blocks modified by an operation that generates no undo; since no undo/rollback data exists for these blocks, the consistent image could not be built. Unlike ORA-01555, the undo was never generated rather than overwritten. (The serializable isolation error is a separate code: ORA-08177.)

Why does it happen?

An operation that generates no undo runs on the same object while the query is in progress: direct-path loads (INSERT /*+ APPEND */, SQL*Loader DIRECT=TRUE), CREATE INDEX / index rebuild or discrete transactions.

How to fix it

Rerun the query after the direct-path load or index operation has finished (retry). Do not schedule long reports and direct-path load / index maintenance jobs on the same object in the same time window. If it recurs, identify the conflicting job with the alert log and ASH and separate the schedules.