Timothy Potter created SOLR-6550:
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Summary: Provide simple mechanism for passing additional metadata
/ context about a server-side SolrException back to the client-side
Key: SOLR-6550
URL: https://issues.apache.org/jira/browse/SOLR-6550
Project: Solr
Issue Type: Improvement
Components: SolrJ
Reporter: Timothy Potter
Assignee: Timothy Potter
While trying to resolve SOLR-6511, it became apparent that I didn't have a good
way to convey more information about a particular error occurring on the
server-side using SolrException. The specific situation I encountered is a
replica took over as leader, but the previous leader wasn't aware of that yet
(due to a Zk session expiration). So when the previous leader (the one that
experienced the Zk session expiration) sent an update request with FROMLEADER,
the new leader rejected the request with a SolrException. Ideally, we want the
new leader to be able to say "you're not the leader anymore" and for the
previous leader to fail the request in a specific way; see SOLR-6511 for more
background on this scenario.
My first inclination was to just extend SolrException and throw a
LeaderChangedException and have the client behave accordingly but then I
discovered that CUSS just takes the status code and error message and
reconstructs a new SolrException (on the client side). HttpSolrServer does the
same thing when creating a RemoteSolrException. So the fact that the
server-side throw a LeaderChangeException is basically lost in translation.
I'm open to other suggestions but here's my approach so far:
Add a {{NamedList<String> metadata}} field to the SolrException class.
If a server-side component wants to add additional context / metadata, then it
will call: {{solrExc.setMetadata("name", "value);}}
When the response is being marshaled into the wire format, ResponseUtils will
include the metadata if available. On the client side, when the response is
processed, the metadata gets included into the new SolrException (in CUSS) or
RemoteSolrException (HttpSolrServer). It's up to the client to dig into the
metadata to take additional steps as I'll be doing in
DistributedUpdateProcessor.
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