Setting up push block notification¶

To check for new blocks Powerpool defaults to polling each of the coinservers you configure. It just runs the rpc call ‘getblockcount’ 5x/second (configurable) to see if the block height has changed. If it has changed, it runs getblocktemplate to grab the new info.

Since polling creates a 100ms delay (on average) for detecting new blocks one optimization is to configure the coinservers to push PowerPool a notification when they accept a new block. Since this reduces the delay to <1ms you’ll end up with fewer orphans. The impact of the faster speed is more pronounced with currencies that have shorter block times.

Although this is an improvement, its worth mentioning that it is pretty minor. We’re talking about shaving off ~100ms or so, which should reduce orphan percentages by ~0.01% - 0.1%, depending on block times. Miners often connect with far more latency than this.

How it push block works¶

Standard Bitcoin/Litecoin based coinservers have a built in config option to allow executing a script right after a new block is discovered. We want to run a script that notifies our PowerPool process to check for a new block.

To accomplish this PowerPool has built in support for receiving a UDP datagram on its monitor port. The basic system flow looks like this:

Coinserver -> Learns of new block Coinserver -> Executes blocknotify script (Alertblock) Alertblock -> Parses the passed in .push file Alertblock -> Sends a UDP datagram based on that .push file PowerPool -> Receives UDP datagram PowerPool -> Runs getblocktemplate on the Coinserver

Note: Using a pushblock script to deliver a UDP datagram to PowerPool can be accomplished in many different ways. We’re going to walk through how we’ve set it up on our own servers, but please note if your server configuration/architechture differs much from ours you may have to adapt this guide.

Modify the coinserver’s config¶

This is the part that tells the coinserver what script to run when it learns of a new block.

blocknotify=/usr/bin/alertblock /home/USER/coinserver_push/vertcoin.push

You’ll want something similar to this in each coinserver’s config. Make sure to restart it after.

Alertblock script¶

Now that the coin server is trying to run /usr/bin/alertblock, you’ll need to make that Alertblock script.

Open your text editor of choice and save this to /usr/bin/alertblock

#!/bin/bash
cat $1 | xargs -P 0 -d '\n' -I ARGS bash -c 'a="ARGS"; args=($a); echo "${args[@]:2}" | nc -4u -w0 -q1 ${args[@]:0:2}'
# For testing the command
#cat $1 | xargs -P 0 -td '\n' -I ARGS bash -xc 'a="ARGS"; args=($a); echo "${args[@]:2}" | nc -4u -w0 -q1 ${args[@]:0:2}'

Block .push script¶

Now your Alertblock script will be looking for a /home/USER/coinserver_push/vertcoin.push file. The data in this file is interpreted by the Alertblock script. It looks at each line and tries to send a UDP packet based on the info. The .push file might contain something like this:

127.0.0.1 6855 VTC getblocktemplate signal=1 __spawn=1

Basically, this tells the Alertblock script to send a UDP datagram to 127.0.0.1 on port 6855. PowerPool will parse the datagram and run getblocktemplate for the currency VTC.

The port (6855) should be the monitor port for the stratum process you want to send the notification to. The currency code (VTC) should match one of the configured currencies in that stratum’s config.

If you need to push to multiple monitor ports just do something like:

127.0.0.1 6855 VTC getblocktemplate signal=1 __spawn=1
127.0.0.1 6856 VTC getblocktemplate signal=1 __spawn=1

For merge mined coins you’ll want something slightly different:

127.0.0.1 6855 DOGE _check_new_jobs signal=1 _single_exec=True __spawn=1

Powerpool config¶

Now we need to update PowerPool’s config to not poll, as it is no longer needed, and makes the coinserver’s logs a lot harder to use. All that needs to be done is set the poll key to False for each currency you have push block setup for.

VTC:
    poll: False
    type: powerpool.jobmanagers.MonitorNetwork
    algo: scryptn
    currency: VTC
    etc...

Confirm it is working¶

You’ll want to double check push block notifications are actually working as planned. The easiest way is to visit PowerPool’s monitoring endpoint and look for the last_signal key. It should be updated each time PowerPool is notified of a block via push block.