Timothy Potter created SOLR-6264:
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Summary: optimize with waitSearcher=true leads to serial execution
across all replicas
Key: SOLR-6264
URL: https://issues.apache.org/jira/browse/SOLR-6264
Project: Solr
Issue Type: Improvement
Components: SolrCloud
Reporter: Timothy Potter
Regardless of whether one agrees with optimizing, when you execute an optimize
request using waitSearcher=true, the requests from the controller node are sent
to each replica in the collection serially.
You can send the optimize command to the update handler for a collection to any
node in the cluster. For instance, if I had a collection named "foo":
curl -i -v http://localhost:8984/solr/foo/update --data-binary '<optimize
maxSegments="1" waitSearcher="true"/>' -H 'Content-type:application/xml'
The node that receives this request will collect the URL for all "live"
replicas in the collection (not just leaders) (see
DistributedUpdateProcessor#getCollectionUrls) and then forward the commit
request to each of them. On the surface, the code looks like it forwards the
request asynchronously to all replicas. However, this is not actually what
happens; the commit requests to each replica in the collection will be
processed serially when using waitSearcher=true (because
ConcurrentUpdateSolrServer's background queue processing is by-passed for
commits).
Bottom-line, if you request the collection to be optimized, the request gets
forwarded around as you'd expect but is done synchronously so can take a long
time.
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