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I am having issues with doing counts on a single table with up to 1million records. I have a 32 core 244gb ram box that I am running my test on so hardware should not be an issue.

I have indexes set up on all of my queries that I am using to perform counts. I have enabled node max_old_space_size to 15gb.

The process I am following is basically looping through a huge array, creating 1000 promises, within each promise I am performing 12 counts, waiting for the promises to all resolve, and then continuing with the next one thousand batch.

As part of my test, I am doing inserts, updates, and reads as well. All of those, are showing great performance up to 20000/sec on each. However, when I get to the portion of my code doing the counts(), I can see via mongostat that there are only 20-30 commands being executed per second. I have not determined at this point, if my node code is only sending that many, or if mongo is queuing it up.

Meanwhile, in my node.js code, all 1000 promises are started and waiting to evaluate. I know this is a lot of info, so please let me know what more granular details I should provide to get some more insight into why the count performance is so slow.

So basically, for a batch of 1000 records, doing lets say 12 counts each, for a total of 12,000 counts, it is taking close to 10 minutes, on a table of 1million records.

MongoDB Native Client v2.2.1 Node v4.2.1

What I'd like to add is that I have tried changing the maxPoolSize on the driver from 100-1000 with no change in performance. I've tried changing my queries that I perform from yield/generator/promise to callbacks wrapped in promise, which has helped somewhat.

The strange thing is, when my program starts, even if i use just the default number of connections which I see as 7 when running mongostat, I can get around 2500 count() queries per second throughout. However, after a few seconds this goes back down to about 300-400. This leads me to believe that mongo can handle that many all the time, but my code is not able to send that many requests, even though I set maxPoolSize to 300 and start 10000 simultaneous promises resolving in parallel. So what gives, any ideas from anyone ?

John
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  • What's your `MongoClient` connection pool size? That determines the potential parallelism of those 1000 promises. – JohnnyHK Jul 22 '16 at 22:21
  • TBH, I have not set any connection pool size. I cannot believe I did not consider that. How do you recommend I go about determining a size I should set ? This will be for a batch process and all connections will be closed after the process is done. – John Jul 22 '16 at 22:31
  • In this scenario, I'd start at 100 and go up from there based on test results. – JohnnyHK Jul 22 '16 at 23:03
  • I actually tried that. I'm not sure if im looking at the right way to profile the number of counts coming through to the server, but im running mongostat and looking at the command field, and see only 30 or 40 ops at a time. Which is very low for the box, and comparatively to 20-30k inserts and update. I even tried setting it to 500, but it just causes connection timeouts. – John Jul 23 '16 at 01:43

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