Noticed this happening on our server. The api calls are split into hourly chunks when solr is polling alfresco for latest transactions. If you havn't changed any documents or document permissions (ACLs) for a while then these API calls get very numerous and repeat every 10 secs or so. We had a test server in this position where we hadn't touched it for a couple of months and noticed the CPU going crazy. By uploading a new document and changing a doc permissions made it all go back to normal.