Running monerod 10.3.1 on a laptop with a Core i5, 8GB RAM and a DSL connection with 16 MBit downstream and it takes roughly 18 minutes (!!!) for synching 200 blocks when running in default mode (i.e. block sync size 200).

When running with --block-sync-size 10 it takes only 2 minutes to sync 200 blocks.

What's the reason behind this? Is there some effort that's superlinear in the block sync size? What are the tradeoffs? I.e. is a block sync size of 10 only recommended in setups similar to mine with moderate CPU and bandwidth?

Why was the default chosen to be 200?


A large block sync size is supposed to make things faster, as some lookups can be made once and reused. However, this uses more memory, and will be slower if it makes the OS start swapping monerod.

I don't know how 200 was chosen, but it was likely a good value for Tacotime, who added the code.

The upcoming release has the block sync size set to 100 prior to fork version 4, and 20 afterwards. This is based on circumstancial evidence, as there is a lack of systematic testing to determine which block sync sizes are better for which (CPU speed, internet speed, memory) confgurations.

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