# operationTime > Depth-first rabbithole dossier for operationTime; source-anchored research pack. Parent: [Causal Consistency](https://llms-explorer.com/tree/causal-consistency/) · 1 facets · 2 facts · page: https://llms-explorer.com/tree/operationtime/ ## Facts and statements - [low] The server reports the operationTime whether the operation succeeded or not, and drivers must save the operationTime in the ClientSession regardless of the operation's success status. Sources: https://raw.githubusercontent.com/mongodb/specifications/master/source/causal-consistency/causal-consistency.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/operationtime-854532108a/rabbithole-synthesis.md#core` - [high] Drivers track the operationTime of the last operation in a session, and each message from a data node in a causally consistent session receives the operationTime, which is the last known logical time persisted in the oplog on that node. Sources: http://muratbuffalo.blogspot.com/2024/04/implementation-of-cluster-wide-logical.html, https://dev.to/franckpachot/read-your-writes-on-replicas-postgresql-wait-for-lsn-and-mongodb-causal-consistency-4he2 — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/operationtime-854532108a/rabbithole-synthesis.md#core`