In case of an erroneous document that causes a Solr exception, the entire batch of documents will not be indexed. In order to identify the erroneous document and to keep indexing the others, the indexing process falls back to index documents one by one instead of a batch. This setting limits the amount of single documents to be indexed per batch to avoid too many commits that might slow doen the Solr server. Setting the value to "0" disables the fallback.