Slow sync speeds from genesis

[CharlieC3]

When syncing a testnet node from genesis, it takes over 12 hours to catch up to chain tip. The testnet we have active is relatively new (<1 month old), so I would think it should catch up to chain tip relatively quickly given the age of the network and simplicity of the TXs within each block.

While this issue only mentions sync speeds in testnet, I would think improving in this area would affect mainnet sync speeds as well.

[wileyj]

Using the branch fix/5676, i ran two separate genesis syncs for testnet using the config in #5676 .

Both syncs took ~2 hours give or take, but one thing i did notice and measured on the second sync was that CPU usage was quite high. other system resources were all in the green, but 2:20 cpus on a local machine were consistently between 50-90% used during the sync duration.

Once synced, the cpu usage went back to baseline.