Context

As part of the lock-free serverStatus effort (SPM-4755), slow serverStatus sections contribute to FTDC gaps when collection exceeds 1 second. Analysis in SERVER-124926 and the slow serverStatus spreadsheet shows that the oplogTruncation section is a significant contributor. The spreadsheet data was collected from live Atlas clusters.

Owning team

Suggested owner (from CODEOWNERS): Oplog (@10gen/server-oplog)

Impact (from slow serverStatus logs)

• Tab: union (mongod + mongos)
• Total duration share: 10.2% of slow-run section time
• Avg duration when slow: 367 ms
• Rows where section exceeded 1s: 0.4% of slow runs

Code location

• Section registration: ServerStatusSectionBuilder<OplogTruncateMarkersServerStatusSection>("oplogTruncation")
• Primary file: src/mongo/db/storage/oplog_cap_maintainer_thread.cpp

Task

Please audit the oplogTruncation serverStatus section and remove any unnecessary blocking work (locks, synchronous I/O, contended atomics, etc.).

Use SKUNK-40 branch for reference implementations and SKUNK-40-nonblocking for nonblocking annotations.

Acceptance criteria

• oplogTruncation section generation does not acquire blocking locks on the hot path
• No regression in section output for FTDC/default serverStatus collection
• Add or update tests if behavior changes

Related work

• Parent analysis: SERVER-124926
• Similar tickets: SERVER-127312 (oplog)