Clojure从数据库获取数据，转换并打印到控制台

Question

I have the following task.
I need to create a console application which takes one param which is the number of data to generate. The data is person address and name. I create a table adress with state, city, zip-code fields. I also create a table with first and last name columns. I use HugSQL to deal with PostgreSQL. So I want to dynamically mix addresses, first and last name and print such the result into the console, the number of generated values depends on the argument passed to the application. This is my code:

(ns project.core
  (:require
    [project.db.get :as get]))

(defn parse-int [s]
  (Integer. (re-find  #"\d+" s )))

(def usa-data (get/usa))

(defn usa-adress-getter []
  (let [data (into {} (shuffle  usa-data))
        city (get data :city)
        state (get data :state)
        zip (get data :zip_code)]
    (str state " " city " " zip)))

(defn repeater [times]
  (dotimes [i times]
    (println (usa-adress-getter))))

(defn -main [value]
  (repeater (parse-int value)))

Here I just check the result of usa-adress-getter function. But the time of the evaluation of function is too big, i have limit which is 1 million values in 1 minutes. How to increase the speed of the evaluation? Function (get/usa) retrieve all data from adress table.

Answer 1

It's difficult to say from this piece of code where the performance bottlenecks are, but here are some tips:

• Use type hints for hotspots. Sometimes the Clojure compiler can't figure out the types, and then type hints can speed things up a lot. In this case, you could set it on the usa-address-getter fn: (defn ^String usa-adress-getter [] ...)
• You could consider modifying your query so that it returns the concatenated string from the database (using an SQL function like concat ). That way, you won't need to get the values from the hash and build the string yourself.
• Printing stuff may be slow, so you could eliminate that, like @leetwinsky says.
• You have to measure in detail the performance of your code, otherwise you won't be able to tell if a modification has gained you some speed. For instance, you could put a timer that prints the number msecs for every 1000 records processed. An of course, only do one change at a time.

Hope this helps.