It is important to get at least this one commit in before the public Nomulus
release so that none of our public users will have to go through this data
migration (although we will have to).
The migration strategy is as follows:
1. Dual-write to non-ReferenceUnion fields in addition to the current
ReferenceUnion fields in use, and add new indexes (this commit). Deploy.
2. Run the ResaveAllEppResourcesAction backfill [].
3. Switch all code over to using the new fields. Dual-write is still in effect,
except it is now copying over the values of the new fields to the old
fields. Switch over all BigQuery reporting scripts to use the new
fields. Deploy.
4. Remove all of the old code and indexes. Deploy.
5. (Optional, at our leisure) Re-run the ResaveAllEppResourcesAction backfill
[] to delete the old obsolete fields.
Note that this migration strategy is rollback-safe at every step -- new data is
not read until it has already been written out in the previous step, and old
data is not removed immediately following a step in which it was still being
read, so the previous step is safe to roll back to.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=136196988
861fd60d2c