# client sessions > Depth-first rabbithole dossier for client sessions; source-anchored research pack. Parent: [Causal Consistency](https://llms-explorer.com/tree/causal-consistency/) · 3 facets · 17 facts · page: https://llms-explorer.com/tree/client-sessions/ ## Problems, failure modes and limitations - Fact 61 mentions "Max has been called on to help in three (3) separate instances" which appears unrelated to client sessions and causal consistency, potentially indicating a data extraction error or irrelevant content. Sources: https://jira.mongodb.org/browse/DRIVERS-2860 — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#disagreements` - [medium] Applications must ensure that only one thread at a time executes operations in a client session, as a session can only be used with the MongoClient object that created it and cannot be used concurrently. Sources: https://www.mongodb.com/docs/manual/core/read-isolation-consistency-recency.md, https://www.mongodb.com/docs/manual/reference/method/Mongo.startSession.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - [low] The following operations build in-memory structures and are not causally consistent, returning an error if associated with a causally consistent client session: $currentOp, getMore, ping, and serverStatus. Sources: https://www.mongodb.com/docs/manual/core/read-isolation-consistency-recency.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - [low] Drivers must raise an error if startSession is called when multiple users are authenticated, and once a ClientSession has ended, drivers must report an error if any operations are attempted with that session. Sources: https://raw.githubusercontent.com/mongodb/specifications/master/source/sessions/driver-sessions.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#troubleshooting` - [low] If sessions are not supported, drivers must raise an error for explicit sessions but must ignore the session for implicit sessions. Sources: https://raw.githubusercontent.com/mongodb/specifications/master/source/sessions/driver-sessions.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#troubleshooting` ## Comparisons and alternatives - Fact 63 lists "Fix Version/s: 3.6.0-rc0" which is a specific release note detail rather than a general functional claim about client sessions. Sources: https://jira.mongodb.org/browse/SERVER-30977 — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#disagreements` - [high] Causal consistency allows clients to wait for a subset of dependent operations rather than a total order, and session consistency guarantees read-your-writes consistency as long as the session exists, though guarantees do not overlap if a new session is created after a failure. Sources: https://jepsen.io/analyses/mongodb-3-6-4, https://www.allthingsdistributed.com/2008/12/eventually_consistent.html — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` ## Facts and statements - [high] MongoDB enables causal consistency through client sessions, a feature introduced in version 3.6 that tracks clusterTime and operationTime to guarantee that causally related operations are observed in the same order. (verified as of 2026-10-15) Sources: https://www.mongodb.com/docs/manual/core/read-isolation-consistency-recency.md, https://raw.githubusercontent.com/mongodb/specifications/master/source/sessions/driver-sessions.md, https://jepsen.io/analyses/mongodb-3-6-4, https://emptysqua.re/blog/how-to-use-mongodb-causal-consistency/, http://muratbuffalo.blogspot.com/2024/04/implementat — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - Fact 62 discusses removing an invariant on non-consistent user input, which is a specific implementation detail or bug fix note not directly describing the general behavior of client sessions. Sources: https://jira.mongodb.org/browse/SERVER-30977 — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#disagreements` - [low] Whether read-your-writes, session, and monotonic consistency can be achieved depends on the "stickiness" of clients to the server, and using sticky sessions makes this explicit, providing an exposure level that clients can reason about. Sources: https://www.allthingsdistributed.com/2008/12/eventually_consistent.html — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - [high] Causally consistent sessions guarantee causal consistency only if associated read operations use "majority" read concern and write operations use "majority" write concern, particularly in the presence of node failures or network partitions. Sources: https://www.mongodb.com/docs/manual/core/read-isolation-consistency-recency.md, https://www.mongodb.com/docs/manual/reference/read-concern.md, https://www.mongodb.com/docs/manual/reference/write-concern.md, https://mongodb.com/blog/post/casual-guarantees-anything-casual, https://emptysqua.re/blog/how-to-use-mongodb-causal-consistency/, http: — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - [low] Read concern "available" and "linearizable" are unavailable for use with causally consistent sessions and transactions, while "local" and "majority" are available with or without such sessions. Sources: https://www.mongodb.com/docs/manual/reference/read-concern.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - [low] Clients require MongoDB drivers updated for MongoDB 3.6 or later to support causal consistency features. (verified as of 2026-10-15) Sources: https://www.mongodb.com/docs/manual/core/read-isolation-consistency-recency.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - [low] The session timeout parameter defines the time in minutes a session remains active after its most recent use, and sessions not receiving new operations or refreshes within this threshold may have their state cleaned up by the server at any time. Sources: https://www.mongodb.com/docs/manual/reference/parameters.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - [low] Drivers must allow multiple calls to endSession or Dispose, ignoring all calls after the first, and can determine if a connection supports sessions by checking if the logicalSessionTimeoutMinutes property in the handshake response has a value. Sources: https://raw.githubusercontent.com/mongodb/specifications/master/source/sessions/driver-sessions.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - [low] The motivation for starting an implicit session for methods that do not take an explicit session parameter is to ensure all commands sent to the server are tagged with a session ID. Sources: https://raw.githubusercontent.com/mongodb/specifications/master/source/sessions/driver-sessions.md — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` - [low] By adding versions on writes, the client discards reads of values with versions that precede the last-seen version, helping maintain consistency. Sources: https://www.allthingsdistributed.com/2008/12/eventually_consistent.html — source: `~/.global-ai-hub/research/.pipeline/mongodb-2026-10-14/frb/client-sessions-79ef1c830d/rabbithole-synthesis.md#core` ## Related concepts - sessions — is a part of client sessions - client — is a part of client sessions