Richard, MergeContent supports a concept called 'correlation attribute' which will merge things together based on a matching correlation attribute value. That might be useful for your case.
Regarding heap use you are observing i'd be happy to work through that more with you. Thanks Joe On Fri, Apr 15, 2016 at 1:45 PM, Richard Miskin <[email protected]> wrote: > Hi Mark, > > Thanks for pointer, I’d not spotted I was losing my provenance information. > I’d changed my code from transferring the temporary FlowFiles to a > relationship that was auto-terminated to using session.remove() and had > assumed that the provenance report was the same. I’ve just tested it and > you’re quite right, using session.remove() discards the provenance > information. > > Heap usage has been an issue, but seems to be okay at present, admittedly > with several GB heap allocated. > > I did look at combining the files using one processor to load the data and > then using MergeContent to combine them. But every record loaded due to a > specific request must be combined into a single file and I couldn’t find a > suitable way of guaranteeing that with MergeContent. > > Thanks for your help, > Richard > >> On 15 Apr 2016, at 17:10, Mark Payne <[email protected]> wrote: >> >> Richard, >> >> So the order of the children may be important for some people. It certainly >> is reasonable to care >> about the order in which the children were created. >> >> The larger concern, though, would be that if we moved to a Set such as >> HashSet, the difference >> in the amount of heap consumed is pretty remarkably different. Since this >> collection is sometimes >> quite large, a Set would be potentially problematic. >> >> That said, with the approach that you are taking, I don't think you're going >> to get the result that >> you are looking for, because as you remove the FlowFiles, the events >> generated for them are >> also removed. So you won't end up getting any Provenance events anyway. >> >> One possible way to achieve what you are looking for is to instead emit each >> of those FlowFiles >> individually and then use a MergeContent processor to merge the FlowFiles >> back together. >> Using this approach, though, you will certainly run into heap concerns if >> you are trying to merge >> 500,000 FlowFiles in a single iterations. Typically, the approach that we >> would follow is to merge >> say 10,000 FlowFiles at a time and then have a subsequent MergeContent that >> would merge >> together 50 of those 10,000-FlowFile-bundles. >> >> Thanks >> -Mark >> >> >>> On Apr 15, 2016, at 11:57 AM, Richard Miskin <[email protected]> wrote: >>> >>> Hi, >>> >>> I’m trying to track down a performance problem that I’ve spotted with a >>> custom NiFi processor that I’ve written. When triggered by an incoming >>> FlowFile, the processor loads many (up to about 500,000) records from a >>> database and produces an output file in a custom format. I’m trying to >>> leverage NiFi provenance to track what has gone into the merged file, so >>> the processor creates individual FlowFiles for each database record >>> parented from the incoming FlowFile and with various attributes set. The >>> output FlowFile is then created as a merge of all the database record >>> FlowFiles. >>> >>> As I don’t require the individual database record FlowFiles outside the >>> processor I call session.remove(Collection<FlowFile>) rather than >>> transferring them. This works fine for small numbers of records, but the >>> call to remove gets very slow as the number of FlowFiles increases, taking >>> over a minute for 100,000 records. >>> >>> I need to do some further testing be sure of the cause, but looking through >>> the code I see that StandardProvenanceEventRecord.Builder contains a >>> List<String> to hold the child uuids. The call to session.remove() >>> eventually calls down to List.remove(), which will get progressively slower >>> as the List grows. >>> >>> Given the entries in the List<String> are uuids, could this reasonably be >>> changed to be a Set<String>? Presumably there should never be duplicates, >>> but does the order of entries matter? >>> >>> Regards, >>> Richard >> >
