[OAK-9112] High CPU IOWAIT on Mongo due to Oak Version Garbage Collection

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 1.8.22
• Component/s: mongomk

Environment

Mongo: 3.4.9
Hosteding: Scalegrid
Instance Size: Small

• Assignee: Unassigned
• Reporter: David Snowsill
• Created: 15/Jun/20 09:44
• Updated: 30/Jun/20 12:52
• Resolved: 29/Jun/20 22:00

Description

Over the previous weekend, our existing application went from having 100,000 documents in the "nodes" collection to 600,000 documents in the "nodes" collection. Since that time there appears to be an Oak background task that commences running near 100% CPU IOWAIT and heavy disk activity (read only). Please refer to charts below

According to currentOp Mongo command, the queries being running look as follows:

{ desc: "conn4944", threadId: "140061124310784", connectionId: 4944, client: "18.207.114.70:47008", clientMetadata: \{ driver: { name: "mongo-java-driver", version: "unknown" }, os: \{ type: "Linux", name: "Linux", architecture: "amd64", version: "4.4.115-k8s" }, platform: "Java/IcedTea/1.8.0_212-b04" }, active: true, opid: 2215767, secs_running: 2, microsecs_running: \{ "$numberLong": "2280333" }, op: "query", ns: "prod-content-service.nodes", query: \{ find: "nodes", filter: { _id: "2:/prod/18d6b4d0-9ee8-4a06-804e-b3669f67dda8" }, limit: 1, singleBatch: true }, planSummary: "IDHACK", numYields: 0, locks: \{ Global: "r", Database: "r", Collection: "r" }, waitingForLock: false, lockStats: \{ Global: { acquireCount: { r: { "$numberLong": "2" } } }, Database: \{ acquireCount: { r: { "$numberLong": "1" } } }, Collection: \{ acquireCount: { r: { "$numberLong": "1" } } } } }

and appears to be iterating over the entire collection.

Can anyone provide any guidance on what is happening?