Not marking with #blocked-on-schema-change because nothing depends on this.
The patch {c84083e} adds a `ar_revid_uniq` index and drops the existing `ar_revid` index, to catch at the database level if future MediaWiki bugs result in rows with duplicate values for ar_rev_id.
From the checklist at https://wikitech.wikimedia.org/wiki/Schema_changes:
# **ALTERs to run:** https://gerrit.wikimedia.org/r/c/429455/10/maintenance/archives/patch-archive-ar_rev_id-unique.sql
# **Where to run those changes:** all.dblist
# **When to run those changes:** No time constraint.
# **If the schema change is backwards compatible:** Yes. I see no index forcing for either of these indexes.
# **If the schema change has been tested already on some of the test/beta wikis:** It'll be automatically deployed to Beta Cluster soon enough, if it hasn't already.
# **if the data should be made available on the labs replicas and/or dumps:** N/A, there is no new data in this change.
Schema change progress:
[] s1
** [x] codfw
** [x] eqiad progress T196379#4407011
[] s2
** [x] codfw
** [x] eqiad progress T196379#4403311
[] s3
** [] codfw
** [] eqiad
[] s4
** [x] codfw
** [x] eqiad progress T196379#4408160
[] s5
** [x] codfw
** [x] eqiad progress T196379#4398629
[] s6
** [x] codfw
** [x] eqiad progress T196379#4402330
[] s7
** [] codfw
** [] eqiad
[] s8
** [] codfw
** [] eqiad