Multiple crawls running at the same time is not a problem. I was rather wondering if you were always performing search queries while crawls were running... This also should not be a problem, but obviously crawling consume resources on your YaCy peer, and therefore when you crawl and search at the same time, all resources are not exclusively available to perform the search.
In web portal mode, you are likely to have consistent performances across search queries (only your YaCy server is requested on its own data), but in peer-to-peer mode many factors may have some impact :
- the network is made of eventually very different kinds of nodes : even if your CPU, memory and network bandwidth are high, it is not necessarily the case of the other peers at the time you search something
- the size of your own peer index (a mix a Solr index and parts of the globally distributed index (RWI)) : with a large local index, your own peer may find rapidly what you search in its own index without need to query the others. On the other hand, when your own index is becoming huge it can affect negatively performances (722000 indexed documents should not be a problem, but with some millions I wouldn't bet)
- the popularity of your search terms : YaCy global index is designed to do its best to distribute homogeneously the index between peers, but every peer eventually choose what is in its own index (by choosing what to crawl, blacklisting, index cleaning operations...). So if you search something that is not already on your peer and is only indexed on a few peers, it may take some time to answer...
- images : images URLs are in the index like any other text resource, but need to be loaded to display some preview. Your YaCy peer has a cache which may contain some images you previously crawled or searched. But when not in the cache, each website originally hosting the image has to be queried concurrently to retrieve it, and some may not answer as quickly as you expect.
I do not pretend to know exactly all implementation details of the current YaCy, but I hope this points will help you have a better understanding of YaCy behavior.