Hi all, I am updating a Solr Collection (Solr 7.3.1 in Cloud mode using SolrJ Java API) with requests that include both adding new documents as well as deleting existing ones (by query). The deletion part is meant to make sure any earlier revisions of the indexed source are deleted as part of the index update. This has worked well for a long time, but in some rare cases, there has been issues where the update process returns success, but the added document(s) are nowhere to be found in the collection.
After some investigation, I'm suspecting that there is an edge case where the delete query can actually overlap the documents added in the same update. Obviously the first suspect to look at here is the delete query, but I also had to start looking into what the documented semantics (if any) for the multi-command update API (JSON update command) actually are. I cannot find any documentation that seems to even touch on this subject. I've looked through most of the online Solr documentation chapters (https://lucene.apache.org/solr/guide/7_3/), though only as an overview. The documentation detailing multi-operation JSON update requests (https://lucene.apache.org/solr/guide/7_3/uploading-data-with-index-handlers.html#solr-style-json - JSON Update Command) doesn't seem to have any details or even link to further reading. I've also read the javadoc for org.apache.solr.client.solrj.request.UpdateRequest (part of SolrJ). Is there is a specific order in which operations in an update request will be executed? Is the order guaranteed for any of the possible operations (add, delete by id / query, optimize, commit) in a single update command? Since I cannot find any details, I have to assume it's undefined and that I should never rely on any order. I suspect that the developers that did this part of our code either assumed it would always be performed in the same order or that the delete query could never overlap. Or perhaps it was just an oversight and we've been lucky so far. Related: in the case where I cannot rely on the operations order in a single update request, is there a recommended way to do these kinds of updates "atomically" in a single request? Ideally, I obviously don't want the collection to be left in a state where the deletion has happened but not the additions or the other way around. Thanks in advance, Andreas
