Run sql in parallel using future: but sql fails
I have the following function
(defn run [x]
(doseq [i (range 1 x)]
(println i)
(future (j/execute! vertica-db ["insert /*+ direct */ into a select * from a limit 1"]))
))
when called with
(run 100)
it will print 1..99, however if you check the row number of table a the row number will not be incremented which means sql is not executed. How do I run sql in parallel?
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1 answer
The only suspicious thing I see in your code is the fact that you never waited for the futures to complete (so maybe not?).
You need to collect the values returned by the calls future
and then lock them until they run out using (deref f)
/ @f
(i.e. dereferencing the future) where f
is one of those values.
Something like this should work:
(defn run [x]
(let [db-insert (fn [i] ((println i) (future (j/execute! vertica-db ["insert /*+ direct */ into a select * from a limit 1"]))))
inserts (doall (map db-insert (range 1 x)))] ;force execution of all the db-insert calls
(doseq [insert inserts] @insert))) ;wait for all the futures to finish
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