(If you don't work with SHA1 values of revisions, you can ignore this message)

Hello,

As part of performance improvements to the revision table, we are reviewing the purpose and usage of the `rev_sha1` field.

Currently, this field is mainly used to detect identical revisions, for example in manual revert detection. The `rev_sha1` value is calculated from the SHA1 values of all slots in the revision, which are stored in the content table:

- The SHA1 of a slot is generated from its content in base36. - For revisions with only one slot (the case for all wikis except Commons), `rev_sha1` matches the SHA1 of that slot. - On Commons, most revisions have two slots ("main" and "mediainfo"). In that case, the SHA1 of the revision is computed by concatenating the SHA1 values of both slots, then hashing that concatenated value again with SHA1.

We have decided to drop the `rev_sha1` field and compute the SHA1 value of a revision on the fly from the `content_sha1` values in its slots.

The same change applies to the archive table: the `ar_sha1` field (for deleted revisions) will also be removed.

If you currently use the `rev_sha1` or `ar_sha1` fields, please switch to using `content_sha1` instead. These fields will be removed from wikireplicas in three weeks.

You can follow progress here: https://phabricator.wikimedia.org/T389026

Thank you, Alexander Vorwerk — IRC: Zabe