Use a serialization library

[brendanlong]

Right now we serialize and deserialize very, very manually (reading and writing one byte at a time). We should see if we can replace that code with something like cstruct. This should make the code more readable, and also make it more efficient.

(I also looked into bitstring and faraday, but they seem lower-level and I don't know if we want that? Faraday is probably more efficient..)

[brendanlong]

I did some experimentation with Angstrom and my basic parser was an order of magnitude slower than Pgx's current code. I might try a little bit more experimentation with flambda. It's also awkward to write since OCaml doesn't have unsigned types, so we either need to use the integers library, which uses C code and is significantly slower, or pass around uint32's as int64's 🤮

[brendanlong]

We should probably look into how PG'OCaml and Postgres_async do serialization and see if we can come up with a base parser/serializer library that they could both theoretically use too.

[brendanlong]

Nevermind, it looks like if we add Async overhead into account, Angstrom_async actually reads data more efficiently than Pgx does, which massively swamps the difference in parse speed:

Estimated testing time 14s (14 benchmarks x 1s). Change using '-quota'.
┌─────────────────────────────────────────────────────────┬────────────┬─────────┬──────────┬──────────┬────────────┐
│ Name                                                    │   Time/Run │ mWd/Run │ mjWd/Run │ Prom/Run │ Percentage │
├─────────────────────────────────────────────────────────┼────────────┼─────────┼──────────┼──────────┼────────────┤
│ Authentication_ok.parse (string)                        │   441.74ns │ 281.26w │          │          │     10.68% │
│ Authentication_ok.parse (bigstring)                     │   403.78ns │ 272.24w │          │          │      9.77% │
│ Authentication_ok_int.parse (string)                    │   190.38ns │ 221.11w │          │          │      4.60% │
│ Authentication_ok_int.parse (bigstring)                 │   123.72ns │ 212.07w │          │          │      2.99% │
│ Authentication_ok_int_lift.parse (string)               │   158.35ns │ 155.09w │          │          │      3.83% │
│ Authentication_ok_int_lift.parse (bigstring)            │    93.14ns │ 146.00w │          │          │      2.25% │
│ Authentication_ok_int_lift.parse (unbuffered bigstring) │    96.23ns │ 169.00w │          │          │      2.33% │
│ Authentication_ok_int_lift.parse (async)                │ 3_497.32ns │ 678.75w │    0.35w │    0.35w │     84.59% │
│ Authentication_ok_int64.parse (string)                  │   205.84ns │ 251.00w │          │          │      4.98% │
│ Authentication_ok_int64.parse (bigstring)               │   146.00ns │ 242.00w │          │          │      3.53% │
│ Authentication_ok_int_simple.parse (string)             │   183.80ns │ 211.00w │          │          │      4.45% │
│ Authentication_ok_int_simple.parse (bigstring)          │   122.37ns │ 202.00w │          │          │      2.96% │
│ Pgx                                                     │    23.40ns │  22.00w │          │          │      0.57% │
│ Pgx_async                                               │ 4_134.51ns │ 639.19w │    0.29w │    0.29w │    100.00% │
└─────────────────────────────────────────────────────────┴────────────┴─────────┴──────────┴──────────┴────────────┘

I'll clean this up and put up a basic repo sometime soon.

[brendanlong]

I started working on this here: https://github.com/brendanlong/ocaml-postgres-protocol