"Term too long (> 245)" error from Xapian when indexing a list migrated from Mailman 2

When indexing a single list (linaro-infrastructure-errors@lists.linaro.org in case I need to reindex it!), the process started displaying warnings like this:

[WARNING/MainProcess] Failed indexing 73001 - 74000 (retry 1/5): Term too long (> 245): +'''''''''''''''''''''''''''''''''''''''''''' (pid 1152909): Term too long (> 245): +'''''''''''''''''''''''''''''''''''''''''''' Traceback (most recent call last): File "/opt/mailman/venv/lib/python3.8/site-packages/haystack/management/commands/update_index.py", line 119, in do_update backend.update(index, current_qs, commit=commit) File "/opt/mailman/venv/lib/python3.8/site-packages/xapian_backend.py", line 476, in update database.replace_document(document_id, document)

We're using xapian-haystack (https://github.com/notanumber/xapian-haystack/tree/master) to go between Haystack and Xapian. There are some closed issues there relating to this message:

https://github.com/notanumber/xapian-haystack/issues/153 https://github.com/notanumber/xapian-haystack/issues/77

Since HyperKitty is just running a command in Haystack, I'm not sure if anything can be done about this but I'm flagging it up in case something can be done 😄