Software Heritage - Datastore Scrubber

Tools to periodically checks data integrity in swh-storage and swh-objstorage, reports errors, and (try to) fix them.

This is a work in progress; some of the components described below do not exist yet (cassandra storage checker, objstorage checker, recovery, and reinjection)

The Scrubber package is made of the following parts:

Checking

Highly parallel processes continuously read objects from a data store, compute checksums, and write any failure in a database, along with the data of the corrupt object.

There is one “checker” for each datastore package: storage (postgresql and cassandra), journal (kafka), and objstorage.

Recovery

Then, from time to time, jobs go through the list of known corrupt objects, and try to recover the original objects, through various means:

  • Brute-forcing variations until they match their checksum

  • Recovering from another data store

  • As a last resort, recovering from known origins, if any

Reinjection

Finally, when an original object is recovered, it is reinjected in the original data store, replacing the corrupt one.

Indices and tables