The Bitcoin Core implementation only keeps a subset of utxos in memory, which by default is only 450 MB. The rest are on disk, which for this thought experiment you say we have plenty of.
Since blocks are limited to 4 MB, we will never have to exceed memory usage to process utxos in a block due to memory.
I don't think a sufficient number of utxos could cause it to fall over and crash.
Are there not db limits?
Also, with a very large amount of db on disk, what are the performance implications, in verifying new blocks? I do understand that this is greatly optimised by what you say, but, even with fast disk, at what point does it get too slow to keep up with the tip?
(interesting that if all spends are of recent utxos, we do kind of magically avoid the most obvious problems, thanks for pointing that out).
(To nostr:nprofile1qqspphpska7kts5gf5pzdk826t2j65xhvecrllwwl062qudnuue05ecpr9mhxue69uhhyetvv9ujuumwdae8gtnnda3kjctv9u9u2c5q and nostr:nprofile1qqsyp0wvpzygmxx5n5plhyall5wvgmvm3uv86zxfljqmft0s45q06tqpzamhxue69uhhyetvv9ujuurjd9kkzmpwdejhgtcppemhxue69uhkummn9ekx7mp0qyvhwumn8ghj7urjv4kkjatd9ec8y6tdv9kzumn9wshsa60yme )
I think there are ways to make validating a block very slow due to script validation, but that is orthogonal to utxo cardinality.
Both blocks and utxos are stored in leveldb, and blocks are an order of magnitude bigger on disk with no performance issues. However, value sizes for utxos are much smaller, so the number of entries is bigger.
The next release of Bitcoin Core has a change to greatly speed up disk lookups of utxos as well.
Oh for sure script validation is a more "real and present danger". I'm discussing more theoretically; the "state" is the utxo set, and theoretically you need all of it to do validation. Blocks, you don't. I think cardinality is relevant, though I'm not sure in detail, based on the size of a utxo serialization being roughly constant.
Lookups in a set aren't free, so a limit must exist somewhere, right?
Yes, I'm trying to find out what that limit would be in leveldb without much luck.
I see some GitHub issue commenters saying they operate leveldb DBs with multiple Tabs and 100s of billions of entries with no issues.
I haven't done the math yet but I think it would take decades of constant utxo spam at a 4 MB per 10 minute rate to get there.
