Error
Error Code:
171
MongoDB Error 171: Parallel Array Indexing
Description
This error occurs when attempting to create a compound index on multiple fields, where each field is an array and these arrays exist in parallel within the same document. MongoDB's multikey indexing mechanism cannot correlate elements across distinct arrays at the same level for a compound index, preventing index creation.
Error Message
Cannot Index Parallel Arrays
Known Causes
3 known causesCompound Index on Parallel Arrays
You tried to create a compound index across two or more distinct array fields that are siblings within the same document.
Multikey Indexing Misunderstanding
Misinterpreting how MongoDB's multikey indexes handle multiple arrays; they are not designed to pair elements from different parallel arrays.
Suboptimal Schema Design
Your document schema places multiple independent array fields at the same hierarchical level, limiting compound indexing options.
Solutions
Coming SoonDetailed step-by-step solutions for this error are being prepared. In the meantime, try these general troubleshooting tips:
General Troubleshooting Tips
- Check the error message carefully for specific details
- Review recent changes that might have caused the error
- Search for the exact error code in the official documentation
- Check log files for additional context
- Try restarting the application or service