rh-feed-speed

rh-feed-speed is a WebSocket block feed latency comparison tool. It connects to multiple WebSocket block sources at the same time, identifies the same block across sources, and compares their block arrival times.

For every block received by all configured sources, rh-feed-speed reports which source received the block first and how much later the other sources received it. The program also generates a latency percentile summary every 5 minutes and exposes JSON summary and Prometheus metrics endpoints.

What does rh-feed-speed do?

rh-feed-speed can be used to:

• Compare block arrival times across multiple WebSocket sources.
• Identify which source received each block first.
• Measure each source’s latency relative to the winning source.
• Calculate p10, p50, p75, p90, p95, p99, and p99.9 latency percentiles.
• Count the number of wins for each source.
• View rolling 5-minute statistics through logs or JSON.
• Export source win counters in Prometheus format.

A block is included in the completed-block statistics only after it has been received by all configured sources.

Features

• Concurrent connections to multiple WebSocket block sources.
• Configurable -source name=url arguments.
• Source-specific subscription messages.
• Block matching by blockHash.
• Fallback matching by block:<blockNumber>.
• Per-block latency and winner output.
• Automatic 5-minute percentile summaries.
• JSON summary endpoint.
• Prometheus metrics endpoint.
• Configurable record retention through -dedup-ttl.
• Debug output for message parsing errors.
• Snapshot-based summary calculation to reduce time spent holding the tracker lock.

Startup

At least one -source name=url argument is required. In practice, two or more sources are usually needed to compare block arrival latency.

go run . \
  -source official=wss://feed.mainnet.chain.robinhood.com \
  -source feeder=wss://us.robinhood-feeder.blockrazor.io/ws/{authToken}

Each source follows this format:

-source name=websocket_url

The source name is used in block details, latency summaries, and Prometheus metric labels.

Viewing block latency

After startup, the program first prints a header:

[block]	sequence_number	block_hash	fast	slow	winner

When the same block has been received by all configured sources, the program prints one detail line:

[block]	12345	0xabc...	0s	18ms	fast

The fields mean:

Field	Description
sequence_number	Sequence number parsed from the WebSocket message.
block_hash	Block hash used to identify the block.
Source column	Source latency relative to the first source that received the block.
winner	Source that received the block first.

In this example, fast received the block first. The slow source received the same block 18ms later.

Five-minute latency summary

The program automatically outputs a latency summary every 5 minutes:

[summary]	type	incremental	window	5m0s	completed_blocks	120
[summary]	type	incremental	source	fast	winner	80	p10	0s	p50	0s	p75	2ms	p90	5ms	p95	8ms	p99	20ms	p99.9	30ms	max	35ms

The summary contains:

Metric	Description
window	Time window used for the summary.
completed_blocks	Number of blocks fully compared in the window.
winner	Number of blocks first received by the source.
p10	10th-percentile latency.
p50	Median latency.
p75	75th-percentile latency.
p90	90th-percentile latency.
p95	95th-percentile latency.
p99	99th-percentile latency.
p99.9	99.9th-percentile latency.
max	Maximum recorded latency.

Each percentile value represents that source’s latency relative to the source that received the corresponding block first.

JSON summary endpoint

Request the current summary in JSON format:

curl http://127.0.0.1:9092/summary

The /summary endpoint currently returns a 5-minute window summary using:

SummaryWithPercentiles(now, 5*time.Minute)

Prometheus metrics

Prometheus metrics are exposed at:

curl http://127.0.0.1:9092/metrics

The currently available metric is:

speed_test_source_wins_total{source="xxx"} 80

This counter records how many fully compared blocks were first received by the specified source.

Summary window behavior

Both the automatic 5-minute summary and the /summary endpoint call:

SummaryWithPercentiles(now, 5*time.Minute)

The implementation generates the summary as follows:

1. Copy a snapshot of the current tracker records.
2. Release the tracker lock.
3. Calculate winner counts and latency percentiles from the snapshot.

This avoids holding the tracker lock during the complete summary calculation.

The window fields are calculated as follows:

• completed_blocks is the number of fully compared blocks in the window.
• winner_counts[].count is the number of wins for each source.
• winner_counts[].percentiles contains the latency percentiles for each source.

Configure -dedup-ttl

Window statistics are based only on records still retained in the tracker. The -dedup-ttl setting therefore directly affects how much data the summary can inspect.

To inspect a complete 5-minute window, set -dedup-ttl to at least 5m. For example:

go run . \
  -dedup-ttl 10m \
  -source official=wss://feed.mainnet.chain.robinhood.com \
  -source feeder=wss://us.robinhood-feeder.blockrazor.io/ws/{authToken}

With the default 30s TTL, the 5-minute summary can only count records from roughly the most recent 30 seconds that have not already been cleaned up.

Recommended relationship:

summary window: 5m
dedup TTL:      >= 5m

Rolling and full summaries

The tracker supports two summary scopes:

Method	Summary scope
SummaryWithPercentiles(now, 5*time.Minute)	Uses retained records from the 5-minute window.
Summary(now, 0)	Uses accumulated WinCount and DelaySamples since the process started.

The automatic logs and HTTP /summary endpoint currently use the 5-minute window summary.

Supported WebSocket message format

Incoming messages are currently parsed according to this JSON structure:

{
  "version": 1,
  "messages": [
    {
      "sequenceNumber": 12345,
      "blockHash": "0xabc...",
      "message": {
        "message": {
          "header": {
            "blockNumber": 100
          }
        }
      }
    }
  ]
}

The parser reads these fields:

JSON field	Usage
messages[].sequenceNumber	Sequence number displayed in block output.
messages[].blockHash	Primary ID used to match the same block across sources.
messages[].message.message.header.blockNumber	Fallback block number when no hash is available.

If a WebSocket message does not contain a recognizable block, it is skipped. When -debug is enabled, parsing errors are printed.

Block matching

Tracker.RecordBlock identifies blocks using the following order:

1. Use blockHash as the block ID.
2. If no block hash is available, use block:<blockNumber>.
3. If the message does not contain a recognizable block, skip it.

The first source to record a block becomes the winner. Delays for later sources are calculated as:

now - FirstSeenAt

The block is marked as completed after all configured sources have received it.

Code flow

The main program flow is implemented in main.go:

1. Parse source, subscription message, metrics, and TTL arguments.
2. Start one WebSocket goroutine for each source.
3. Send the corresponding -source-subscribe message after the WebSocket connects.
4. Parse messages[].blockHash, sequenceNumber, and blockNumber.
5. Pass the block to Tracker.RecordBlock.
6. Use the block hash as the block ID or block:<blockNumber> as the fallback.
7. Record the first source as the winner.
8. Calculate the delays for later sources.
9. Mark the block as completed after every source has received it.
10. Print the block details.
11. Increment the winner’s Prometheus counter.
12. Store records in a min-heap ordered by FirstSeenAt.
13. Index records by block ID for fast lookup.
14. Continuously remove expired records from the heap head.
15. Copy a snapshot before calculating the summary and release the lock.

FAQ

What is rh-feed-speed?

rh-feed-speed is a program that compares the arrival time of the same block across multiple WebSocket block sources.

How many sources are required?

At least one source is required to start the program. Two or more sources are usually needed to compare latency.

How is the fastest source determined?

The first configured source to receive a block is recorded as the winner. Other source delays are calculated relative to that first arrival.

When is a block counted as completed?

A block is counted as completed after it has been received by all configured sources.

Why does the five-minute summary contain less than five minutes of records?

The summary can only use records still retained by the tracker. If -dedup-ttl is shorter than five minutes, older records may be removed before the summary is calculated.

What value should be used for -dedup-ttl?

Use at least -dedup-ttl 5m when the complete five-minute summary window is required. The original example uses -dedup-ttl 10m.

What happens if a message has no block hash?

If a block number is available, the tracker uses block:<blockNumber> as the block ID. Otherwise, the message is skipped.

Which Prometheus metric is available?

The current metric is speed_test_source_wins_total, which counts wins for each source.

How can parsing errors be viewed?

Enable -debug to print message parsing errors.