They can stay in the memory pool forever because consensus process will never
accept these transactions (and maybe even block consensus process at all).
We're paging these hashes, so we need a previous full page and a current one
plus some cache for various requests. Storing 1M of hashes is 32M of memory
and it grows quickly. It also seriously affects node startup time, most of
what it's doing is reading these hashes, the longer the chain the more time it
needs to do that.
Notice that this doesn't change the underlying DB scheme in any way.
If we only have genesis block (or <2000 headers) then we might as well use
generic logic below with zero targetHash because genesis block has zero
PrevHash (and its hash will naturally be the last on the chain going
backwards).
Sometimes it can be hard to persist all changes at ones, the process
can take almost all RAM and a lot of time. Here's the example of reset
for mainnet from 2.4M to 1:
```
anna@kiwi:~/Documents/GitProjects/nspcc-dev/neo-go$ ./bin/neo-go db reset -m --height 1
2022-11-20T17:16:48.236+0300 INFO MaxBlockSize is not set or wrong, setting default value {"MaxBlockSize": 262144}
2022-11-20T17:16:48.236+0300 INFO MaxBlockSystemFee is not set or wrong, setting default value {"MaxBlockSystemFee": 900000000000}
2022-11-20T17:16:48.237+0300 INFO MaxTransactionsPerBlock is not set or wrong, using default value {"MaxTransactionsPerBlock": 512}
2022-11-20T17:16:48.237+0300 INFO MaxValidUntilBlockIncrement is not set or wrong, using default value {"MaxValidUntilBlockIncrement": 5760}
2022-11-20T17:16:48.240+0300 INFO restoring blockchain {"version": "0.2.6"}
2022-11-20T17:16:48.297+0300 INFO initialize state reset {"target height": 1}
2022-11-20T17:16:48.300+0300 INFO trying to reset blocks, transactions and AERs
2022-11-20T17:19:29.313+0300 INFO blocks, transactions ans AERs are reset {"took": "2m41.015126493s", "keys": 3958420}
...
```
To avoid OOM killer, split blocks reset into multiple stages. It increases
operation time due to intermediate DB persists, but makes things cleaner, the
result for almost the same DB height with the new approach:
```
anna@kiwi:~/Documents/GitProjects/nspcc-dev/neo-go$ ./bin/neo-go db reset -m --height 1
2022-11-20T17:39:42.023+0300 INFO MaxBlockSize is not set or wrong, setting default value {"MaxBlockSize": 262144}
2022-11-20T17:39:42.023+0300 INFO MaxBlockSystemFee is not set or wrong, setting default value {"MaxBlockSystemFee": 900000000000}
2022-11-20T17:39:42.023+0300 INFO MaxTransactionsPerBlock is not set or wrong, using default value {"MaxTransactionsPerBlock": 512}
2022-11-20T17:39:42.023+0300 INFO MaxValidUntilBlockIncrement is not set or wrong, using default value {"MaxValidUntilBlockIncrement": 5760}
2022-11-20T17:39:42.026+0300 INFO restoring blockchain {"version": "0.2.6"}
2022-11-20T17:39:42.071+0300 INFO initialize state reset {"target height": 1}
2022-11-20T17:39:42.073+0300 INFO trying to reset blocks, transactions and AERs
2022-11-20T17:40:11.735+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 1, "took": "29.66363737s", "keys": 210973}
2022-11-20T17:40:33.574+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 2, "took": "21.839208683s", "keys": 241203}
2022-11-20T17:41:29.325+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 3, "took": "55.750698386s", "keys": 250593}
2022-11-20T17:42:12.532+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 4, "took": "43.205892757s", "keys": 321896}
2022-11-20T17:43:07.978+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 5, "took": "55.445398156s", "keys": 334822}
2022-11-20T17:43:35.603+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 6, "took": "27.625292032s", "keys": 317131}
2022-11-20T17:43:51.747+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 7, "took": "16.144359017s", "keys": 355832}
2022-11-20T17:44:05.176+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 8, "took": "13.428733899s", "keys": 357690}
2022-11-20T17:44:32.895+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 9, "took": "27.718548783s", "keys": 393356}
2022-11-20T17:44:51.814+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 10, "took": "18.917954658s", "keys": 366492}
2022-11-20T17:45:07.208+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 11, "took": "15.392642196s", "keys": 326030}
2022-11-20T17:45:18.776+0300 INFO intermediate batch of removed blocks, transactions and AERs is persisted {"batches persisted": 12, "took": "11.568255716s", "keys": 299884}
2022-11-20T17:45:25.862+0300 INFO last batch of removed blocks, transactions and AERs is persisted {"batches persisted": 13, "took": "7.086079594s", "keys": 190399}
2022-11-20T17:45:25.862+0300 INFO blocks, transactions ans AERs are reset {"took": "5m43.791214084s", "overall persisted keys": 3966301}
...
```
We need to keep the headers information consistent with header batches
and headers. This comit fixes the bug with failing blockchain
initialization on recovering from state reset interrupted after the
second stage (blocks/txs/AERs removal):
```
anna@kiwi:~/Documents/GitProjects/nspcc-dev/neo-go$ ./bin/neo-go db reset -t --height 83000
2022-11-20T16:28:29.437+0300 INFO MaxValidUntilBlockIncrement is not set or wrong, using default value {"MaxValidUntilBlockIncrement": 5760}
2022-11-20T16:28:29.440+0300 INFO restoring blockchain {"version": "0.2.6"}
failed to create Blockchain instance: could not initialize blockchain: could not get header 1898cd356a4a2688ed1c6c7ba1fd6ba7d516959d8add3f8dd26232474d4539bd: key not found
```
Don't use cache because it's not yet initialized. Also, perform
safety checks only if state reset wasn't yet started. These fixes
alloww to solve the following problem while recovering from
interrupted state reset:
```
anna@kiwi:~/Documents/GitProjects/nspcc-dev/neo-go$ ./bin/neo-go db reset -t --height 83000
2022-11-20T15:51:31.431+0300 INFO MaxValidUntilBlockIncrement is not set or wrong, using default value {"MaxValidUntilBlockIncrement": 5760}
2022-11-20T15:51:31.434+0300 INFO restoring blockchain {"version": "0.2.6"}
failed to create Blockchain instance: could not initialize blockchain: current block height is 0, can't reset state to height 83000
```
When block is being spread through the network we can get a lot of invs with
the same hash. Some more stale nodes may also announce previous or some
earlier block. We can avoid full DB lookup for them and minimize inv handling
time (timeouts in inv handler had happened in #2744).
It doesn't affect tests, just makes node a little less likely to spend some
considerable amount of time in the inv handler.
Blockchain's notificationDispatcher sends events to channels and these
channels must be read from. Unfortunately, regular service shutdown procedure
does unsubscription first (outside of the read loop) and only then drains the
channel. While it waits for unsubscription request to be accepted
notificationDispatcher can try pushing more data into the same channel which
will lead to a deadlock. Reading in the same method solves this, any number of
events can be pushed until unsub channel accepts the data.
Which allows to enable/disable the service, change nodes, keys and other
settings. Unfortunately, atomic.Value doesn't allow Store(nil), so we have to
store a pointer there that can point to nil interface.
It's not an ideal solution, but at least it solves the problem for
now. Caveats:
* consensus only needs one method, so it's mirrored to Blockchain
* rpcsrv uses core.* definition of the StateRoot (so technically it might as
well not have an internal Ledger), but it uses core already unfortunately
1. It's not good for pkg/core to import anything from pkg/neorpc.
2. The type is closely tied to the state package, even though it's not stored
in the DB
Specifying a certain stateroot R as `invoke*historic` RPC-call
parameter, we're willing to perform historic call based on the storage
state of root R. Thus, next block should be of the height h(R)+1. This
allows to use historic functionality for the current blockchain height.
name old time/op new time/op delta
TokenTransferLog_Append-8 93.0µs ±170% 46.8µs ±152% ~ (p=0.053 n=10+9)
name old alloc/op new alloc/op delta
TokenTransferLog_Append-8 53.8kB ± 4% 38.6kB ±39% -28.26% (p=0.004 n=8+10)
name old allocs/op new allocs/op delta
TokenTransferLog_Append-8 384 ± 0% 128 ± 0% -66.67% (p=0.000 n=10+10)
