User merge/delete slow since notes consolidation fix

[Chris Sharp]

Found on PINES production running Evergreen 3.8.0.

Merging a user in 3.6 was basically instantaneous, but since our upgrade to Evergreen 3.8.0, we've seen very long delays in merging patrons. Analysis of the DB functions led to slowness in this line in actor.usr_purge_data:

UPDATE actor.usr_message SET editor = dest_usr WHERE editor = src_usr;

EXPLAIN revealed a seq scan on the actor.usr_message table, which is very large in PINES.

After taking a look at actor.usr_message, I realized we are missing an index on the "editor" column.

Branch adding that index on the way.

To fix in a running production system, run the following command:

CREATE INDEX CONCURRENTLY aum_editor ON actor.usr_message (editor);

[Chris Sharp (chrissharp123)]

Branch to add the index is here:

https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/csharp/lp1960956_fix_slow_patron_merge_delete

[Terran McCanna (tmccanna)]

Noting that PINES has this in production and it has helped significantly.

[Bill Erickson (berick)]

Looks good. Merged to 3.8 / master.