Groov Write Queue Full

How many pending writes does the groov AR1 support and how fast are writes written between the onboard Node-Red server and the groov server? I’ve got an application in which I’m querying a device via Ethernet TCP/IP (once a second), parsing the response, then writing tags to the groov server (32 tags at once). Everything was fine with one device connected. Then I added a second device (runs simultaneously in its own flow) and noticed that the number of writes in the queue (as seen in the Node-Red window) kept creeping up (e.g. 32, 64, 96, etc.) until it finally gave me queue full errors in the debug console. I put in lock flags so that each device won’t get queried until all of its writes are finished. Seemed to work, so I added a third flow to handle a third device. Now I’m seeing the same thing, even with lock flags. Each flow is writing up to 32 tags at once, almost simultaneously. At what point does the groov starting rejecting writes because the queue is full?

BTW, multiple writes are accomplished by creating an array of tags then using a split. I saw that mentioned in another post. This might be more efficient if there was a groov node that could write multiple tags at once but I don’t think that exists.

groov itself doesn’t do the queueing: it just handles the writes as quickly as possible. The groov API nodes that we publish for Node-RED handle queueing within the node; I think they’ll queue up to 500* writes before rejecting new stuff, but I’ll have to ask around to be sure.

If your writes are going through a single write node, then the writes are done sequentially in first in, first out order, as fast as groov responds to them.

Providing batch writes through the API has been on my todo list for awhile, just haven’t gotten a chance to get to it yet.

Oh, and what version of groov View are you running? There have been some speed improvements since the Data Store API was originally released, though it’s still not as fast as it really should be. There are some architectural issues in the way (data store values are stored in the project database, which is only accessible via a single threaded job queue) and some iffy decisions that I need to revisit.

Thanks for the reply. It’s version R4.1c (r53943). I know there’s a new version, R4.1e, though I haven’t updated yet. I was definitely getting queue full errors when running multiple flows all writing to the groov. I changed the inject time to 2 seconds from 1 second and ran it over the weekend. That seems to relieve it because there are no write errors now.

I am having the same issue while running R4.2a.

Are there any tips on ways to optimize how data is written to groov View from Node-RED?

@Jonathan_Fischer would it be better to funnel all writes to groov through a single flow rather than independent flows? Or does that not matter?

I don’t think that’ll matter: the developer responsible for maintaining the Node-RED nodes indicated that the queue is shared across all flows.

When triggering say 10 multiple write, or multiple read Nodes in 1 flow.

  1. Would it matter be more efficient if I connect nodes in parallel, or in series?
  2. Do I need to add delay node in between trigger?
  3. What if I have total 50 read/write nodes all triggered by inject node with 1s repeatedly?

*In the past I have experience qued label will accumulate to >30 when PAC is busy.

Thinking out loud here…

Have you guys thought about using prime numbers for your scan rates rather than hitting everything exactly once a second (or at some 1 second multiple)?

You can put fractional inject rates in the inject node, its not stuck at 1 second intervals.
So have one flow at 1.1 second, another at 1.9 and the third at 2.3. Better still if you can spread them even more. Here are some primes that would be interesting to test;
1.1, 1.3, 1.7, 1.9, 2.3, 2.9, 3.1, 3.7, 4.1

The key is to balance functionally with performance.

1 Like

I don’t really have good answers to any of these. It might just come down to “give it a try and see if it helps”. :persevere:

There is a definite bottleneck in data store writes, and it’s vexing enough people that I’m bumping it up as a high priority for the next major release.

2 Likes