Solana Head Detection: slotSubscribe vs blockSubscribe

Summary

This PR replaces the expensive blockSubscribe WebSocket subscription with the lightweight slotSubscribe approach for Solana head detection. The change reduces WebSocket bandwidth by 95% while maintaining the same real-time performance.

Problem

The blockSubscribe API has significant drawbacks:

• High bandwidth: ~1KB per notification (full block data)
• Unstable API: Requires --rpc-pubsub-enable-block-subscription node flag
• Limited support: Not available on most RPC providers (premium tier only)

Solution

Use slotSubscribe with throttled getBlockHeight HTTP calls:

• ~50 bytes per notification (only slot/parent/root numbers)
• Stable API: No special flags required
• Universal support: Works with all Solana RPC providers
• Throttled HTTP calls: Every 5 slots (~20% of slot notifications)

Benchmark Results

Synthetic Benchmark (100 slots)

Real Production Test (Solana Mainnet, ~11 minutes each)

Daily Extrapolation (24 hours)

Implementation Details

slotSubscribe Notification Format

{"slot": 112301554, "parent": 112301553, "root": 112301500}

~50 bytes per notification

Throttling Logic

• Check actual block height via HTTP every 5 slots
• Between checks, use cached height value
• On HTTP error, fallback to cached height or use slot as height

Synthetic Hash

Since slotSubscribe doesn't provide block hash, we generate a deterministic synthetic hash from slot:

val syntheticHash = BlockId.from(ByteBuffer.allocate(32).putLong(slot).array())

This ensures ForkChoice deduplication works correctly.

Conclusion

slotSubscribe is the recommended approach because:

1. 93% less total bandwidth (15.5 MB vs 217 MB per day)
2. Stable API - no special node flags required
3. Universal provider support - works with all Solana RPC providers
4. Identical head update rate - same real-time performance
5. Zero errors in production testing

The trade-off of ~46K HTTP calls/day is acceptable:

• Each call is lightweight (~100 bytes response)
• Total HTTP bandwidth is only ~4.7 MB/day
• HTTP calls are throttled (every 5 slots, not every slot)