# Config-server task-executor pool fan-out during 9.0 upgrades > Source-anchored research for Config-server task-executor pool fan-out during 9.0 upgrades. Run status: COMPLETED. Parent: [MongoDB Upgrade Paths](https://llms-explorer.com/tree/mongodb-upgrade-paths/) · 5 facets · 13 facts · page: https://llms-explorer.com/tree/config-server-task-executor-pool-fan-out-during-9-0-upgrades/ ## 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](https://www.mongodb.com/docs/manual/reference/parameters.md) ## 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](https://www.mongodb.com/docs/manual/release-notes/9.0.md) ## 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](https://jira.mongodb.org/browse/SERVER-136226) ## 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](https://www.mongodb.com/docs/manual/reference/parameters.md) ## 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](https://www.mongodb.com/docs/manual/release-notes/9.0.md) - 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](https://www.mongodb.com/docs/manual/reference/parameters.md) - 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](https://help.aliyun.com/en/mongodb/user-guide/parameters-available-in-mongodb-4-2) - 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](https://yandex.cloud/ru/docs/storedoc/api-ref/Cluster/list) - 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](https://github.com/mongodb/mongo/blob/master/src/mongo/s/sharding_task_executor_pool.idl) - 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](https://jira.mongodb.org/browse/SERVER-136226) - 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](https://www.mongodb.com/docs/manual/release-notes/9.0.md) - 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](https://www.mongodb.com/docs/manual/release-notes/9.0.md) - 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](https://jira.mongodb.org/browse/SERVER-136448)