(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
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