Large slack import issues on mattermost 5.18.0


we have some issues trying to import a large Slack backup (1GB compressed 11GB uncompressed) to mattermost, we are using mm 5.18.0 and using the CLI to import the original zip file from the corporate slack export (with private channels and direct messages).

when trying to import the complete export, the server show a large number of import errors regarding file ids not being found besides bot accounts not being created (bots are not important). So as a debug, we created a single day export of the last available day on slack (4.5 MB compressed), when trying to import this file, we always end up with a server error mattermost panic: runtime error: invalid memory address or nil pointer dereference after a few channel import errors regarding channel name length.

at the moment we are trying to import a new fresh export to discard export file corruption (this process has taken around 7 hours to complete at it seams that the import file process before committing changes is single thread)

any ideas???

FYI we are importing using the command sudo -u mattermost ./bin/mattermost import slack <team name> <file name>


to solve this issue, we needed to split the import in parts, DMs, Group DMs, Private and public channels, add the user manifest to each and also delete every DM where the SlackBot was involved because this bot is not included in the user manifest, and the import utility breaks when there are conversations with users not refered on it (you can also try to add the SlackBot user manually, we didn’t try that.)

in our case the import of 10+ GB of uncompressed conversations and channels took arround 3 days to complete.

Don’t know if still useful but i think this and then /mattermost/bin/mattermost import bulk bulk-export.jsonl could be a different way that seams to be faster

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i think is worth the shot, i’m going to try it for a future sync from the old slack account before the final migration.