A new column named `cuc_only_for_read_old` will be used to indicate whether a row in `cu_changes` exists in either `cu_log_event` or `cu_private_event`, with a value of `1` indicating that it does. When the value is `1` the row will not be selected if also reading from the new tables.
This column will be removed once the migration in T324907 has been completed and is intended to be temporary. Without this temporary column CheckUser would not know whether a given row in cu_changes exists in the other tables.
# **ALTERs to run:** https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/CheckUser/+/022f35b72c3b379394483101d78a78c761677a35/schema/mysql/patch-cu_changes-add-cuc_only_for_read_old.sql
# **Where to run those changes:** all
# **When to run those changes:** At any time
# **If the schema change is backwards compatible:** Yes.
# **If the schema change has been tested already on some of the test/beta wikis:** checkuser is not on beta cluster - Will test on checkuser-beta-wiki.wmcloud.org shortly.
# **if the data should be made available on the labs replicas and/or dumps:** Everything is private
Progress:
[x] s1
[x] s2
[] s3
[] s4 (eqiad is done)
[x] s5
[x] s6
[x] s7
[] s8 (eqiad is done)
[x] labtestwiki