The target for range indexes in a MarkLogic database should be about 100. This is because:

• In the interests of performance, MarkLogic Server indexes your content on ingest, then memory maps those indexes to serialized data structures on disk. Each of those memory maps requires some amount of RAM.
  • If you've got many thousands of indexes you may run into a situation where system monitoring is reporting you've got RAM to spare, but MarkLogic Server is reporting "SVC-MAPINI: Mapped file initialization error." In which case you're likely running up against Linux's default vm.max_map_count value.
  • Independent of SVC-MAPINI errors, the more range indexes you've configured, the longer it will take to perform forest operations.
• If you find yourself configuring many hundreds or even thousands of range indexes, you should migrate your data modeling scheme to take advantage of Template Driven Extraction (TDE), which was specifically engineered to address this scenario.

Additional Reading:

• "The index behind TDE views is the triple index, not range indexes. We heard that people hit a memory limit when they created many columns (and therefore many range indexes) in the same database – the limit was hundreds, and people wanted to create tens of thousands. Now there is no effective limit to the number of columns you can create in a database." (https://developer.marklogic.com/learn/tde-faq/)
• "If you find yourself planning to make thousands (or even hundreds) of range indexes, it’s probably worth stepping back and rethinking about how the data will be represented." (https://www.marklogic.com/blog/10000-range-indexes/)
• "Spread a large number of columns across multiple TDEs, instead of having a single TDE containing all those same columns" (https://help.marklogic.com/Knowledgebase/Article/View/draft-best-practices-for-using-marklogic-semantics-at-scale)
• "If your index settings have a very large number of range indexes specified (on the order of thousands or even tens of thousands), you may find your MarkLogic Server instance returning a message saying that it "Cannot allocate memory" - even when your OS monitoring metrics indicate that there appears to be plenty of unused RAM." (https://help.marklogic.com/Knowledgebase/Article/View/121/0/range-indexes-and-mapped-file-initialization-errors)