It doesn't cost much, but it's used _a lot_, so optimizing it makes sense.
name old time/op new time/op delta
TxHash-8 4.89ns ± 5% 0.54ns ± 2% -88.86% (p=0.008 n=5+5)
name old alloc/op new alloc/op delta
TxHash-8 0.00B 0.00B ~ (all equal)
name old allocs/op new allocs/op delta
TxHash-8 0.00 0.00 ~ (all equal)
We're likely to have something comparable to the current changeset in the
subsequent one. If it's bigger, no big deal, it'll be reallocated, if it's
smaller, no big deal, the next one will be preallocated smaller.
It's very effective in avoiding allocations for big.Int, we don't have a
microbenchmark for memppol, but this improves TPS metrics by ~1-2%, so it's
noticeable.
Problem: transactions with wrong hashes are accepted to the chain if
consensus nodes are designated as Oracle nodes. The result is wrong
MerkleRoot for the accepted block. Consensus nodes got such blocks
right from the dbft and store them without errors, but if
non-consensus nodes are present in the network, they just can't accept
these "bad" blocks:
```
2021-11-29T12:56:40.533+0300 WARN blockQueue: failed adding block into the blockchain {"error": "invalid block: MerkleRoot mismatch (expected a866b57ad637934f7a7700e3635a549387e644970b42681d865a54c3b3a46122, calculated d465aafabaf4539a3f619d373d178eeeeab7acb9847e746e398706c8c1582bf8)", "blockHeight": 17, "nextIndex": 18}
```
This problem happens because of transaction hash caching. We can't set
transaction hash if transaction construction wasn't yet completed.
Problem:
```
--- FAIL: TestMemCachedPersist (0.07s)
--- FAIL: TestMemCachedPersist/BoltDBStore (0.07s)
testing.go:894: TempDir RemoveAll cleanup: remove C:\Users\Anna\AppData\Local\Temp\TestMemCachedPersist_BoltDBStore294966711\001\test_bolt_db: The process cannot access the file because it is being used by another process.
```
Solution:
Release the resources occupied by the DB.
We use 2 prefixes for storing items because of state synchronization.
This commit allows to parametrize dao with the default prefix.
Signed-off-by: Evgeniy Stratonikov <evgeniy@nspcc.ru>
b9be892bf9 has made Persist asynchronous which
is very effective in allowing the system to continue processing
blocks/transactions while flushing things to disk. It at the same time is very
dangerous in that if the disk is slow and it takes much time to flush KV set
(more than persisting interval), there might be even bigger new KV set in
MemCachedStore by the time it finishes. Even if the system immediately starts
to flush this new data set it (being bigger) can take more time than the
previous one. And while doing so a new data set will appear in memory,
potentially again bigger than this.
So we can easily end up with the system going out of control, consuming more
and more memory and taking more and more time to persist a single set of
data. To avoid this we need to detect such condition and just wait for Persist
to really finish its job and release the resources.
Everywhere it matters (and that's callExFromNative() now) it's incremented
already, so when we're doing Call() at the same time (and it's done to invoke
`_initialize` method) we're effectively double-incrementing it.
Standards are NEP-11 and NEP-17, not NEP11, not NEP17, not anything
else. Variable/function names of course can use whatever fits, but documents
and comments should be consistent wrt this.
