No in-place updates with router.field set

[James <ja...@ohrt.info>]

Steps to reproduce:

Use Solr in SolrCloud mode.
Create collection with implicit routing and router.field set to some field,
e.g. "routerfield".
Index very small document. Stop time -> X
Index very large document. Stop time -> Y
Apply update to large document. Note that update command has at least three
entries:
{
 "ID":1133,
 "Property_2":{"set":124},
 "routerfield":"FirstShard"
 }
QTime of update will always be closer to Y than to X.

If I repeat these steps without setting router.field while creating the
collection, QTime of update will be very close X.


From this simple test I conclude that router.field somehow prevents updates
from being performed as in-place updates.
Can anyone confirm? Is this a bug? Anybody care to open a Jira item if
necessary?

According to the first comment on
https://issues.apache.org/jira/browse/SOLR-8889 the router.field option is
hardly tested and there seem to be also other related problems.