Geoffrey Jacoby created HBASE-23710:
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             Summary: Priority configuration for system coprocessors
                 Key: HBASE-23710
                 URL: https://issues.apache.org/jira/browse/HBASE-23710
             Project: HBase
          Issue Type: New Feature
          Components: Coprocessors
            Reporter: Geoffrey Jacoby
            Assignee: Geoffrey Jacoby


Currenty HBase allows operators to set system region coprocessors via 
hbase-site.xml to be loaded on each table in a cluster (or alternately, all 
tables but system tables). HBase assumes that the first loaded system 
coprocessor gets the first, or SYSTEM priority, with each subsequent system 
coproc getting incremented by 1. As a reminder, in HBase _lower_ priorities go 
first. 

It can be useful for an operator to be able to define a coprocessor on each 
table that needs a different priority. For example, an operator might want a 
coproc to load on each table _last_, so that it can enforce some system 
invariant and know that no other coproc will interfere with it. 

I propose adding optional priority config to the hbase-site.xml configuration, 
separated from each coproc class in the comma-separated list by a special 
character (perhaps a colon) that's not used in class names. 

The region coprocessor host will parse the priority if present and use it when 
instantiating the coproc. 



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