- Is that a bug with the lucene infinspan postgres combination or a wrong usage?
Lucene continuously merges multiple segments into one according to defined policies, and during this process, up to 3x more space than the index size can be used temporarily.
If your system is under heavy writing, merges will be more frequent and it's reasonable the extra space being used as you described, up to Gbs of space depending on the size of the index.
I suggest you try to use the property "hibernate.search.default.indexwriter.merge_max_size" to avoid big merges. By doing so, you will end up with more segments in
your index at a performance penalty on searches (which may not be significant to you) but less temporary space will be using during routine merges.
EDIT: If not using Hibernate Search to maintain the Lucene indexes, the equivalent way of achieving this is setting it directly in the Lucene merge policy, for example
"setMaxMergeMB( value )" if using TieredMergePolicy