Saving and restoring undo stack at shutdown and startup

[linhuang-blockone]

Change Description

This PR saves RocksDB backing store undo stack when shutdown and restores undo stack upon startup.

This is a draft PR calling for review and quick turn around of resolving any design/coding issues.

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• Documentation

• Stability bug fix

• Other

• Other - special case

Testing Changes

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Consensus Changes

• Consensus Changes

API Changes

• API Changes

Documentation Additions

• Documentation Additions

In <the configured data-dir>/state directory, a new file undo_stack.dat is introduced if --backing-store rocksdb is used . It saves RocksDB undo stack's state before node shutdown and is used to restore nodeos's undo stack at startup.

[brianjohnson5972]

Is there a reason we don't just do this in the constructor for kv_db? It is passed cfg.

[linhuang-blockone]

I will change to use constructor of kv_db.

[brianjohnson5972]

Do you know why you needed to remove this? I don't think you should need a copy constructor.

[linhuang-blockone]

Thanks! Tim also spot this. I have changed it back in the next commit.

[TimothyBanks]

Thanks for the help Lin.

[linhuang-blockone]

Thanks for the help Lin.

Thank you Tim, Bucky, and Brian for all the help. My last commit made it serialization and deserialization work (I verified via logging). I will incorporate your other comments shortly.

[larryk85]

So, instead of making this struct and reflecting it. What you should do is this then.

Instead of using the FC_REFLECT, because the internals of shared_bytes are not very usable through reflection.

Add two public methods to shared_bytes:

template <typename Stream>
inline Stream& operator<<(Stream& ds, const shared_bytes& b) {
   ds << b.size();
   ds.write(b.data(), b.size());
   return ds;
}

and

template <typename Stream>
inline Stream& operator>>(Stream& ds, shared_bytes& b) {
   std::size_t sz;
   ds >> sz;
   shared_bytes tmp = {sz};
   ds.read(tmp.data(), tmp.size());
   b = tmp;
   return ds;
}

[TimothyBanks]

shared_bytes already has an out stream overload and a method that can create a shared_bytes from a hex string (which is what is streamed out). You would just need to provide the operator for streaming in.

[larryk85]

If you implement the above methods for shared_bytes, this becomes...

shared_bytes key;
ds >> key;

shared_bytes value;
ds >> value;

[linhuang-blockone]

Thanks for the suggestion! This simplifies the code. Changed.

[larryk85]

with the datastream operators this would become...

out << key;
out << value;

[linhuang-blockone]

Changed.