I'm not sure what happened, but as of about two weeks, the queries ran by GUC seem to hit a snag somewhere. It now quite often takes anywhere from 80s to over 250s for a request to get a response where previously the same requests came back in just a second or two.
Example: `https://tools.wmflabs.org/guc/?user=Krinkle&debug=true`
Using GUC's debug mode to print information about connections and queries, I see that in most cases the biggest part of the delay is from a single query, usually the first "user" query.
This is odd, for a number of reasons.
1. The first database listed doesn't appear be technically different from the others (relatively small wiki and less than 50 rows in total for that username).
2. The first "user" query is not the first query overall on that connection, so it's not about being the first query.
3. The given query is relatively simple compared to the much bigger query before it. See below, "Query all wikis for matching revisions" is a huge union query across 100+ wikis at once for the revision tables, taking only <70ms. Then after that is a user table query for one database, taking 88 seconds?
Debug sample 1/2:
```
+0s: Got input, start search
+0s: Get list of all wikis
+0s: Create connection to s1.web.db.svc.eqiad.wmflabs
+0.07s: Query all wikis for matching revisions
+88.97s: Query user data for ab.wikipedia.org
+0.03s: Query contributions on ab.wikipedia.org
+0.05s: Query user data for ace.wikipedia.org
+0.03s: Query contributions on ace.wikipedia.org
+0.03s: Query user data for ady.wikipedia.org
+0.03s: Query contributions on ady.wikipedia.org
+0.03s: Query user data for af.wikipedia.org
+0.04s: Query contributions on af.wikipedia.org
...
... etc., etc. – 800 times more for other wikis
```
Debug sample 2/2:
```
+0s: Got input, start search
+0s: Get list of all wikis
+0s: Create connection to s1.web.db.svc.eqiad.wmflabs
+0.05s: Query all wikis for matching revisions
+20.95s: Query user data for ab.wikipedia.org
+0.03s: Query contributions on ab.wikipedia.org
+0.08s: Query user data for ace.wikipedia.org
+0.02s: Query contributions on ace.wikipedia.org
+0.03s: Query user data for ady.wikipedia.org
...
... etc., etc.
```