@Dave0x1 Typically MergeContent processor will utilize a lot of heap when the number of FlowFiles being merged in a single execution is very high and/or the size of the FlowFile's attributes are very large. While FlowFiles queued in a connection will have the FlowFile attributes/metadata held in NiFi heap, there is a swap threshold at which time NiFi swaps FlowFile attributes to disk. When it comes to MergeContent, FlowFile are allocated to bins (will still show in inbound connection count). FlowFiles allocated to bin(s) can not be swapped. So if you set min/max num flowfiles or min/max size to a large value, it would result in large amounts of heap usage. Note: FlowFile content is not held in heap by mergeContent. So the way to create very large merged files while keeping heap usage lower is by chaining multiple mergeContent processor together in series. So you merge a batch of FlowFiles in first MergeContent and then merge those into larger merged FlowFile in a second MergeContent. Also be mindful of extracting content to FlowFile attributes or generating FlowFile attributes with large values to help minimize heap usage. Please help our community thrive. If you found any of the suggestions/solutions provided helped you with solving your issue or answering your question, please take a moment to login and click "Accept as Solution" on one or more of them that helped. Thank you, Matt
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