Mergers are DPL devices able to merge ROOT objects produced in parallel. Topologies of mergers can be created using the
o2::experimental::mergers::MergerInfrastructureBuilder class. To generate only one Merger, one can also use o2::experimental::mergers::MergerBuilder.
Mergers provide a handful of options which are listed in the include/Mergers/MergerConfig.h file.
See the snippet from src/mergersTopologyExample.cxx as a usage example:
...
void customize(std::vector<CompletionPolicy>& policies)
{
MergerBuilder::customizeInfrastructure(policies);
}
#include <Framework/runDataProcessing.h>
...
using namespace o2::experimental::mergers;
MergerInfrastructureBuilder mergersBuilder;
mergersBuilder.setInfrastructureName("histos");
mergersBuilder.setInputSpecs(mergersInputs);
mergersBuilder.setOutputSpec({{ "main" }, "TST", "HISTO", 0 });
MergerConfig config;
config.ownershipMode = { OwnershipMode::Integral };
config.publicationDecision = { PublicationDecision::EachNSeconds, 5};
config.mergingTime = { MergingTime::BeforePublication};
config.timespan = {Timespan::FullHistory};
config.topologySize = { TopologySize::NumberOfLayers, 2};
mergersBuilder.setConfig(config);
mergersBuilder.generateInfrastructure(specs);
...It creates a 2-layer topology of Mergers, which will consume mergerInputs and send merged object on the Output
{{"main"}, "TST", "HISTO", 0 }. The infrastructure will integrate the received differences and each 5 seconds it will
merge and publish the merged object. It will consist of a full history of the data that topology will have received.