Multiple database queries in parallel, for a single client request

问题

To complete certain requests from the user, in my application, I am issuing multiple DB queries from a single method, but they are currently being executed sequentially & thus the application is blocked until the time it has received the response/data for the previous query, then proceeding to next query. This is not something I like much. I would like to issue parallel queries.

Also after issuing queries I would like to do some other work, (instead of being blocked till previous queries response) & on getting the response for each query I would like to execute a code block specific to each query's data. What is the way to do this ?

Edit:My DB API does provide connection pooling.

I'm just a little bit familiar with Java multithreading.

Using:-
------
Java 1.6
Cassandra 1.1 Database with Hector

回答1:

You should understand before you start doing this

To benefit from concurrency, you need to have multiple db connections. THe best way to solve this is to create a db pool.
You need to create a runnable / callable class for executing a db Statement. You will need to put together some messaging system to alert listeners to when your query has completed
Understand that when you are sending multiple requests at the same time, all bets are off as to which will complete first, and that there may be conflicts between statements that destabilize your app.

回答2:

I have the similar task/issue. For complete build result I need to send few requests for few different service (few on REST, few on Thrift), for decrease latency I need to sent it in parallel. My idea is using java.util.concurrent.Future, make simple aggregation manager , which create many requests together and will be wait last retrieved response and return all needed data. In more advanced solution this manager can make/combine final result during other queries, but this solution can be not thread safe.

回答3:

Here's a very trivial/limited approach:

final Connection conn = ...;
final Object[] result = new Object[1];
Thread t1 = new Thread(new Runnable() {
    public void run() {
        Object results = conn.executeQuery();
        result[0] = results;
    }
});
t1.setName("DBQueryWorker");
t1.start();
// do other work
while (t1.isAlive()) {
   // wait on thread one
}

This is a simple approach, but many others are possible (eg, thread pooling via Java Concurrency task executors, Spring task executors, etc).

来源：https://stackoverflow.com/questions/9932653/multiple-database-queries-in-parallel-for-a-single-client-request

标签

java

multithreading

parallel-processing

hector