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```2026-02-15 23:50:36 source WARN debezium-mongod...
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2026-02-15 23:50:36 source WARN debezium-mongodbconnector-mongodb_srv___axlehire-prod-us-west1.vuags.mongodb.net_-replicator-fetcher-0 i.d.c.m.e.BufferingChangeStreamCursor$EventFetcher(enqueue):285 Unable to acquire buffer lock, buffer queue is likely full
2026-02-15 23:50:37 source INFO pool-2-thread-1 i.a.c.i.d.AirbyteDebeziumHandler$CapacityReportingBlockingQueue(reportQueueUtilization):48 CDC events queue stats: size=9554, cap=446, puts=7, polls=0
2026-02-15 23:50:38 source WARN debezium-mongodbconnector-mongodb_srv___axlehire-prod-us-west1.vuags.mongodb.net_-replicator-fetcher-0 i.d.c.m.e.BufferingChangeStreamCursor$EventFetcher(enqueue):285 Unable to acquire buffer lock, buffer queue is likely full
2026-02-15 23:50:39 source WARN debezium-mongodbconnector-mongodb_srv___axlehire-prod-us-west1.vuags.mongodb.net_-replicator-fetcher-0 i.d.c.m.e.BufferingChangeStreamCursor$EventFetcher(enqueue):285 Unable to acquire buffer lock, buffer queue is likely full
2026-02-15 23:50:39 source WARN debezium-mongodbconnector-mongodb_srv___axlehire-prod-us-west1.vuags.mongodb.net_-replicator-fetcher-0 i.d.c.m.e.BufferingChangeStreamCursor$EventFetcher(enqueue):285 Unable to acquire buffer lock, buffer queue is likely full
2026-02-15 23:50:39 source INFO pool-2-thread-1 i.d.c.c.BaseSourceTask(logStatistics):323 4529 records sent during previous 00:00:39.628, last recorded offset of {server_id=mongodb_srv___axlehire-prod-us-west1.vuags.mongodb.net_} partition is {sec=1771173763, ord=340, resume_token=826991F783000001542B042C0100296E5A1004D7F8B7A147F14F5AA4105EE790C486F8463C6F7065726174696F6E54797065003C696E736572740046646F63756D656E744B65790046645F696400646991F7835744304B7490CCF1000004}
2026-02-15 23:50:39 source WARN debezium-mongodbconnector-mongodb_srv___axlehire-prod-us-west1.vuags.mongodb.net_-replicator-fetcher-0 i.d.c.m.e.BufferingChangeStreamCursor$EventFetcher(enqueue):285 Unable to acquire buffer lock, buffer queue is likely full
2026-02-15 23:50:39 source INFO main i.a.c.i.d.i.DebeziumRecordIterator(computeNext):87 CDC events queue poll(): blocked for PT0.00001587S after 60 previous call(s) which were not logged.
2026-02-15 23:50:39 source INFO main i.a.c.i.d.i.DebeziumRecordIterator(computeNext):184 CDC events queue poll(): returned a change event with "source": {"version":"2.6.2.Final","connector":"mongodb","name":"mongodb_srv___axlehire-prod-us-west1.vuags.mongodb.net_","ts_ms":1771173698000,"snapshot":null,"db":"prod","sequence":null,"ts_us":1771173698000000,"ts_ns":1771173698000000000,"collection":"routing_route","ord":529,"lsid":null,"txnNumber":null,"wallTime":1771173698937}.
2026-02-15 23:50:46 source INFO Malformed non-Airbyte record (connectionId = 5118e68a-138a-44f4-9044-803b1fbbf3b6): Terminating due to java.lang.OutOfMemoryError: Java heap space
k
The logs show Debezium’s MongoDB change stream buffer and Airbyte’s CDC events queue filling up until the Java process runs out of heap: • 
BufferingChangeStreamCursor$EventFetcher(enqueue): ... buffer queue is likely full
• 
CDC events queue stats: size=9554, cap=446, puts=7, polls=0
• Final error: 
Terminating due to java.lang.OutOfMemoryError: Java heap space
From the available knowledge sources, there is no explicit, documented fix for this specific MongoDB CDC + Debezium + Java heap space pattern. The closest related information is: • MongoDB CDC in Airbyte relies on change streams and the oplog; long-running or heavy CDC can stress resources and cause failures if the system cannot keep up. [MongoDB v2 troubleshooting] • There is an open issue where CDC queues fill and eventually lead to 
java.lang.OutOfMemoryError: Java heap space
, indicating that under high CDC load the current implementation can exhaust memory. [Mongo OOM issue] • There is also an open issue that OutOfMemory in orchestration components is currently blocking some CDC pipelines, and resource configuration for these components is under active discussion. [Orchestrator OOM issue] Because the docs and issues do not provide a concrete, supported workaround for your exact error, I can only suggest directions that are implied but not explicitly documented as fixes: 1. Reduce CDC pressure / event volume Anything that lowers the rate or size of change events (e.g., fewer collections in CDC, less write volume during sync, or temporarily switching some high‑volume collections to Full Refresh instead of Incremental CDC) will reduce pressure on the Debezium buffer and Airbyte CDC queue. This is consistent with the general CDC limitations and performance concerns described for MongoDB. [MongoDB v2 troubleshooting] 2. Check for very large documents / events Large MongoDB documents can cause issues in CDC; while the docs focus on 
BSONObjectTooLarge
and the 16 MB limit, the same large events also increase memory usage in the CDC pipeline. The documented mitigations (restructuring large documents, switching to Full Refresh, or deselecting problematic streams) may indirectly help with memory pressure. [MongoDB v2 troubleshooting] 3. Track the related open issues Your logs and error pattern are very similar to the open MongoDB OOM issue and the orchestrator OOM issue; both are still open and described as blocking for some CDC workloads, which suggests there may not yet be a fully resolved product-level fix. [Mongo OOM issue; Orchestrator OOM issue] Because the knowledge sources do not document a definitive configuration change (e.g., a specific memory flag, queue size setting, or connector option) that resolves this, I cannot provide a guaranteed fix. The most accurate guidance based on the sources is: • Treat this as a known limitation / open issue with MongoDB CDC under high load. • Mitigate by reducing CDC volume and large documents where possible. • Monitor and follow the linked GitHub issues for an upstream fix or official workaround. 👍 0 button 👎 0 button ℹ️ Tip: Mention @kapa.ai in the thread for follow-ups or DM the app for 1-to-1 help.
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