# dropIndexes abort semantics > Source-anchored research for dropIndexes abort semantics. Run status: COMPLETED. Parent: [MongoDB Wildcard and Hidden Indexes, Index Builds and Index Overhead](https://llms-explorer.com/tree/mongodb-wildcard-and-hidden-indexes-index-builds-and-index-overhead/) · 2 facets · 8 facts · page: https://llms-explorer.com/tree/dropindexes-abort-semantics/ ## Comparisons and alternatives - The current manual allows `dropIndexes` to remove a ready index while a different index on the same collection is building. Earlier versions returned `BackgroundOperationInProgressForNamespace` for that separate-index case. This differs from aborting a build, which targets the full builder set. (high confidence) (verified as of 2026-10-20) — [source](https://www.mongodb.com/docs/manual/reference/command/dropIndexes.md) - MongoDB's `SERVER-37726` implementation record says aborting an in-progress build emits an `abortIndexBuild` oplog entry instead of a separate `dropIndexes` oplog entry. It gives rollback/refetch consistency as the reason for that choice. (low confidence) — [source](https://jira.mongodb.org/browse/SERVER-37726) ## Facts and statements - MongoDB 4.4 and later allow dropIndexes or its dropIndex helper to target an in-progress index; MongoDB attempts to stop that build, with the same effect as dropping the built index. (high confidence) (verified as of 2026-10-20) — [source](https://www.mongodb.com/docs/manual/reference/command/dropIndexes.md) - For a replica set, issue the abort request on the primary. The primary stops the build and writes an `abortIndexBuild` oplog entry; secondaries that apply it stop the in-progress build and discard their local build job. MongoDB warns against using `killOp` to terminate in-progress builds in replica sets or sharded clusters. (high confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/manual/reference/command/dropIndexes.md) - An abort targets the whole index builder. If one `createIndexes` call started several indexes together, the caller must specify every index name from that builder; the server matches the request against the builder's complete index-name set. (high confidence) (verified as of 2026-10-20) — [source](https://raw.githubusercontent.com/mongodb/mongo/master/src/mongo/db/index_builds/index_builds_coordinator.cpp) - MongoDB's current manual says not to use killOp to terminate an in-progress index build in a replica set or sharded cluster; issue dropIndexes on the primary instead. (high confidence) (verified as of 2026-10-19) — [source](https://www.mongodb.com/docs/manual/core/index-creation/) - If `dropIndexes` names an index that is still being built, the command attempts to stop that build; MongoDB documents stopping it as having the same effect as dropping the completed index. (high confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/manual/reference/command/dropIndexes.md) - MongoDB's `SERVER-46397` ticket documents a historical race: two concurrent `dropIndexes` commands on a primary could make a secondary block while applying one drop against another active build, preventing a later `abortIndexBuild` from applying. The ticket lists fixes in 4.4.0-rc0 and 4.7.0. (low confidence) — [source](https://jira.mongodb.org/browse/SERVER-46397)