Extremely slow OAI metadata retrieval through Dublin Core

(OJS version 3.1.2.0)

Upon validating OAI-PMH data on http://validator.oaipmh.com/ with http://historiaregional.org/ojs/index.php/historiaregional/oai (the journal in question), though ListRecords for OAI_MARC, MARCXML and RFC1807 work correctly, OAI_DC provides no response at all, as if it had timed out.

Indeed, when checking directly with http://historiaregional.org/ojs/index.php/historiaregional/oai?verb=ListRecords&metadataPrefix=oai_dc it takes several minutes for the site to provide the XML data.

What could be causing the delay for this Dublin Core format in particular?

Hi, we have the same problem and the problem was on mysql with this two changes resolve it

innodb_flush_log_at_trx_commit = 2

and change mysql tmp directory into ram