feat(share/eds/accessor_cache): rate limit cache rotation.

[walldiss]

Implementation ideas

eds accessor cache is limited in size by 128 items. Based on observations of BN, evection rate from cache could be quite high:

Such high rate of cache eviction causes several issues:

• If accessor is evicted while it is being read, it causes panic in dagstore (should be fixed by latest dagstore update)
• (after update) If accessor is evicted while it is being read, it will result in read error and will not serve requested data
• high cache rotation, means there is very little benefit of having cache at all, since accessors are recreated very often.
• if there there are more unique headers are sampled from node, then cache size, it could cause to server unable to serve any data. Cache will be rotated by evictions, while also failing requests.

Solutions:

• Fast: disable cache. It will prevent concurrent close from eviction on opened accessor while it is being read. But will remove any boost from cache
• Harder: introduce cache rotation rate limit. There should be timed budget (evictions/sec), that will rotate the cache if budget is > 0. When budget is used, it prevents storing to cache until budget is reset.

[distractedm1nd]

Removing cache is not that easy because we have to rethink where we are calling close. Also, it makes serving shrex for new blocks less efficient

[distractedm1nd]

We could, however, disable cache for blockstore only, so that the cache is only used for shrex eds requests. But this will probably noticeably damage LN sampling performance