Patch: https://gerrit.wikimedia.org/r/#/c/318553/22/maintenance/archives/patch-l10n_cache-primary-key.sql
```
DELETE FROM /*$wgDBprefix*/l10n_cache; -- Or truncate- truncate is faster but it has metadata locking issues
ALTER TABLE /*$wgDBprefix*/l10n_cache DROP KEY /*i*/lc_lang_key, ADD PRIMARY KEY(lc_lang, lc_key)
```
All wikis. Nice to have, but not urgent (but should be easy). It may be already done on some wikis: T146591#3139282
Truncation done at: T150306
Schema change progress:
[] s1
** [x] codfw
** [x] eqiad progress T146591#4407008
[] s2
** [x] codfw
** [x] eqiad progress T146591#4403312
[] s3
** [] codfw
** [] eqiad
[] s4
** [x] codfw
** [x] eqiad progress T146591#4408161
[] s5
** [x] codfw
** [x] eqiad progress T146591#4398630
[] s6
** [x] codfw
** [x] eqiad progress T146591#4402331
[] s7
** [] codfw
** [] eqiad
[] s8
** [x] codfw
** [] eqiad