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The setting you need has to do with formdataUploadLimitInKB that is found in solrconfig.xml
If you take a look at your solrconfig.xml file, there is an area that sets that up.
Open up your opensolr index:
Go to the Config Files Editor tab
Select solrconfig.xml
Scroll down until you see a directive like:
There, you'll see the settings:
So,  is what you needed to change in your own solrconfig.xml file in your indexes.
HOWEVER #1: If you need a ridiculous amount of boolean clauses (as solr calls them), you won't be able to do it, since solr will always return an error: too many boolean clauses
You can fix that, by increasing the parameter maxBooleanClauses in your solrconfig.xml
HOWEVER #2: For better query performance, you could use or think of different alternative techniques to your issue, such as maybe split your very large 1 query into multiple queries and aggregate the results in your own app.
For example:
Query 1:*:*&fq=field_name:(VAL1 OR ... OR VALn)
- where n is a number that is less than the maxBooleanClauses set in your solrconfig.xml
Query 2:*:*&fq=field_name:(VALn+1 OR ... OR VALm)
- where m is a number that is less than the maxBooleanClauses set in your solrconfig.xml
Query i... (you get the point)
You then merge the results from all those queries.
You can figure out the number of queries you have to make by dividing the number of OR clauses you need by the maxBooleanClauses setting in your solrconfig.xml
And, needless to say, if you have your data replicated on multiple servers behind a load balancer (AKA our Opensolr Resilient Cluster Solution),  your multiple queries would be load balanced, which in return results in much faster queries and better resiliency.