Informix Error -875: Incompatible Access Mode and Isolation Level.

Reasons / Common Causes

-875 fires when SET TRANSACTION combines READ WRITE access mode with READ UNCOMMITTED isolation level — per the official guidance, that specific combination isn't allowed.

1. SET TRANSACTION READ WRITE combined with ISOLATION LEVEL READ UNCOMMITTED, per the official guidance — the direct, only cause; READ UNCOMMITTED (dirty read) semantics aren't compatible with a transaction that intends to write.

Solutions / Resolution

1. Use a different isolation level with READ WRITE, per the official guidance's implied fix — READ COMMITTED, REPEATABLE READ, or SERIALIZABLE are all compatible with READ WRITE.
2. Or use READ ONLY access mode if READ UNCOMMITTED isolation is genuinely needed, since that combination is permitted.

Examples

The disallowed combination

SET TRANSACTION READ WRITE, ISOLATION LEVEL READ UNCOMMITTED;
-- -875: READ WRITE can't combine with READ UNCOMMITTED

Corrected — a compatible isolation level

SET TRANSACTION READ WRITE, ISOLATION LEVEL READ COMMITTED;

Or corrected — READ ONLY with READ UNCOMMITTED

SET TRANSACTION READ ONLY, ISOLATION LEVEL READ UNCOMMITTED;

Diagnostic Checks

1. Check the combination of access mode and isolation level in the SET TRANSACTION statement — READ WRITE specifically can't pair with READ UNCOMMITTED.

Related Errors / Related Topics

• -877 — "Isolation Level previously set by 'Set Transaction'." A related SET TRANSACTION error, about conflicting subsequent isolation-level statements.
• -878 — "Invalid operation for a READ-ONLY transaction." A related SET TRANSACTION error, about attempting to write within a READ ONLY transaction.

READ WRITE and READ UNCOMMITTED can't combine — use READ ONLY if uncommitted-read semantics are genuinely needed.