<p>Hey everyone,</p>
<p>I'm slowly learning the concurrency principles integrated into the Go programming language.</p>
<p>I wrote on paper what my app will look like. It will consist of n channels that will make network requests. The result of each channel will then be piped to n channels that will make database queries (most likely Redis).</p>
<p>In other languages that I've used in the past (like Node.js), the database driver was initialised once and created a connection pool of by default (usually) 5 connections to the database.</p>
<p>My question is the following, if you have n channels that will make database queries, shouldn't you also set the connection pool size to n connections ?</p>
<p>Thanks in advance!</p>
<hr/>**评论：**<br/><br/>jjolla888: <pre><p>if the db requests are being performed faster than the incoming network requests, you should be ok to reduce the db pool size by the proportionate amount</p>
<p>the other way is a little less determinate - if your db responses are slow such that your network gatherers are twiddling their thumbs, increasing the number of concurrent connections may not help - as it will depend on both your db and requesters hardware capabilities. </p></pre>calebdoxsey: <pre><p>You only need 2 channels.</p>
<pre><code>var c1 chan databaseRequest
var c2 chan redisRequest
</code></pre>
<p>Then make workers pull off the same channel:</p>
<pre><code>for i :=0; i < numberOfDatabaseWorkers; i++ {
go func() {
for {
req := <-c1
// do database stuff
c2 <- redisRequest{}
}
}()
}
for i := 0; i < numberOfRedisWorkers; i++ {
go func() {
for {
req := <-c2
// do redis stuff
}
}()
}
</code></pre>
<p>For cleanup you can either close the first channel, wait for all the database workers to finish and the close the second (look at <code>sync.WaitGroup</code> to see how to do that), or I tend to prefer some sort of <code>exit</code> channel that you close once and pass to every worker. Then every time they do a send/receive do it in a select:</p>
<pre><code>select {
case <-exit: // when exit is closed this will happen
return
case req = <-c1:
}
</code></pre>
<p>As for the connection pool, <code>database/sql</code> is already using one. You can adjust the number of connections it will make with <a href="http://godoc.org/database/sql#DB.SetMaxOpenConns" rel="nofollow">http://godoc.org/database/sql#DB.SetMaxOpenConns</a>.</p>
<p>I would first try it with the defaults and then if you are concerned about performance start tinkering with the options and benchmark/profile.</p>
<p>But the defaults are pretty good and worrying about it now may be a sign of premature optimization.</p></pre>
