Simulate "this IndexReader is closed" ?

[Richard Goodman]

Hi there,

I've spent time implementing the solr prometheus exporter into our Solr
environment. During this, I did come across an issue where when I was
getting the core level metris, I was getting exceptions.

Digging into this further, I realised it's actually on the Solr side of
this, in particular, the metrics that come from the following group within
each core;

SEARCHER.*


An example of the output I was getting;

{
  "responseHeader":{
    "status":500,
    "QTime":44},
  "error":{
    "msg":"this IndexReader is closed",
    "trace":"org.apache.lucene.store.AlreadyClosedException: this
IndexReader is closed\n\tat
org.apache.lucene.index.IndexReader.ensureOpen(IndexReader.java:257)\n\tat
org.apache.lucene.index.StandardDirectoryReader.getVersion(StandardDirectoryReader.java:339)\n\tat
org.apache.lucene.index.FilterDirectoryReader.getVersion(FilterDirectoryReader.java:127)\n\tat
org.apache.lucene.index.FilterDirectoryReader.getVersion(FilterDirectoryReader.java:127)\n\tat
org.apache.solr.search.SolrIndexSearcher.lambda$initializeMetrics$13(SolrIndexSearcher.java:2268)


I changed my metric calls to include "&regex=^(?!SEARCHER).*" and the
results were coming through *(minus the SEARCHER metrics)*.

This was enough to unblock me from getting the rest of the metrics,
however, I want to revisit this and see what I can do, as from my point of
view, this is a bug within Solr, because it breaks the entire metrics API *(for
example, if you just hit /solr/admin/metrics and the IndexReader is Closed,
it'll return this message and 0 metrics will be collected/displayed)*.

My problem is, I'm not entirely sure how to replica this error? and was
hoping I could find some guidance. I saw that the file "
org/apache/solr/search/SolrIndexSearcher.java" has the metrics in them, but
got a bit lost from first glance.

If anyone has any information that could help me;
1. Replicate the issue
2. Explain what exactly does it mean when IndexReader is closed

I would be really grateful,

Kind Regards,
Richard Goodman