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Accumulo >> mail # user >> number of query threads for batch scanner

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number of query threads for batch scanner
I have a table with 4 tablets on a given tablet server. Depending on the
numQueryThreads parameter below, I see a varying number of maximum
concurrent scans on that table. This maximum number varies from 1 to 3
(i.e., some values for numQueryThreads result in maximum concurrent scan of
1, some values result in 2 concurrent scans, etc.). Can someone shed light
on what is the relationship between numQueryThreads and number of
concurrent scans?

public BatchScanner createBatchScanner(String tableName,
                                       Authorizations authorizations,
                                       int numQueryThreads)

A follow-on question would be what is general rule of thumb for setting
numQueryThreads? Should it be set to the  # of hosted tablets expected to
be consumed by that BatchScanner? Should it be the # of tablet servers
expected to be hit by that BatchScanner? Something else?