Config-server task-executor pool fan-out during 9.0 upgrades
Parent: MongoDB Upgrade Paths · Published reference · snapshot 2026-10-27
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Source-anchored research for Config-server task-executor pool fan-out during 9.0 upgrades. Run status: COMPLETED.
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Definitions
- ShardingTaskExecutorPoolMinSizeForConfigServers is a config-server-specific override of the minimum outbound connections per TaskExecutor pool. MongoDB documents -1 as inheritance from ShardingTaskExecutorPoolMinSize and permits startup or runtime configuration; Yandex's managed-service API separately exposes the same config-server minimum override. (medium confidence) [source]
How it works
- For dedicated config servers, when ShardingTaskExecutorPoolMinSize exceeds 1, the release notes prescribe ShardingTaskExecutorPoolMinSizeForConfigServers=1 before upgrading to an impacted 9.0 release. For embedded config servers, they prescribe contacting MongoDB Support before upgrading. (low confidence) (verified as of 2026-10-14) [source]
Problems, failure modes and limitations
- SERVER-136226 identifies ShardingFixed as a connection pool created by all mongos and mongod nodes to communicate with config servers. Reusing ShardingTaskExecutorPoolMinSize for that pool can exhaust config-server connections; the 9.0 release notes independently describe the same failure within MongoDB's own documentation. (high confidence) [source]
Comparisons and alternatives
- ShardingTaskExecutorPoolMinSize controls a TaskExecutor pool minimum rather than an application-driver pool setting. MongoDB documents a default of 1 and a per-destination mongod minimum; Alibaba's MongoDB 4.2 service documentation separately describes a default of 1 and a minimum per TaskExecutor pool for sharded instances. The older service documentation does not establish 9.0 defect status. (medium confidence) [source]
Facts and statements
- The 9.0 known-issues table identifies SERVER-136226 for 9.0.0 and later and warns of config-server unavailability. (low confidence) (verified as of 2026-10-14) [source]
- ShardingTaskExecutorPoolMinSizeForConfigServers overrides the ordinary minimum for pools targeting config servers. Its default -1 inherits the ordinary minimum; it supports startup and runtime changes. The manual labels it new in 6.0. (high confidence) [source]
- As historical managed-service context, Alibaba’s MongoDB 4.2 parameter table describes ShardingTaskExecutorPoolMinSize as a minimum per TaskExecutor pool and taskExecutorPoolSize as the number of pools on a mongos. This does not establish 9.0 defaults or defect applicability. (low confidence) [source]
- Yandex Cloud’s Cluster.List API exposes shardingTaskExecutorPoolMinSizeForConfigServers as an optional config-server pool minimum override. This corroborates provider configuration exposure, not availability of MongoDB 9.0 or remediation for SERVER-136226. (low confidence) (verified as of 2026-10-27) [source]
- The development master IDL defines ShardingFixedTaskExecutorPoolMinSize with default 1 and explicitly excludes both ShardingTaskExecutorPoolMinSize and ShardingTaskExecutorPoolMinSizeForConfigServers from that fixed pool. This development state does not identify a released 9.0 fix version. (low confidence) (verified as of 2026-10-27) [source]
- SERVER-136226 is Closed with Resolution Fixed, was resolved October 16, 2026, and was last updated October 23, 2026. Its Fix Version/s field is None. This does not identify a released 9.0 patch containing the fix. (low confidence) (verified as of 2026-10-23) [source]
- The release-notes snapshot labels SERVER-136226 as affecting 9.0.0 and later. If ShardingTaskExecutorPoolMinSize exceeds 1, it directs operators of clusters with dedicated config servers to set ShardingTaskExecutorPoolMinSizeForConfigServers to 1 before upgrading to an impacted 9.0 release. This is a conditional mitigation, not a blanket claim that every default-configured upgrade exhausts connections. (low confidence) (verified as of 2026-10-14) [source]
- For clusters with embedded config servers, the 9.0 release notes direct operators to contact MongoDB Support before upgrading for an appropriate deployment-specific configuration. The dedicated-config-server mitigation is not documented there as universally appropriate for embedded config servers. (low confidence) (verified as of 2026-10-14) [source]
- SERVER-136448 repeats the ShardingFixed connection-exhaustion description and is closed as Duplicate of SERVER-136226. It is another record of the same issue, not a second independent incident or research origin. (low confidence) (verified as of 2026-10-06) [source]
Children
- No children recorded.