Improve parser creation formance.

[pereman2]

Hello and sorry for the intrusion but... I was running some benchmark for https://github.com/penberg/limbo and I found out Parser::new was doing a whole bunch of memmove due to the stack approach used by SmallVec. This PR removes SmallVec in favor of Vec as you will see proven as worth it, by the benchmarks you guys have inside benches/sqlparser_bench.rs:

This move creates a huge different in Parser::new, and when I say huge, I say a whopping 1444% difference. SmallVec triggers too many memmoves.

# With Vec::new()  ------------------------------------------------
     Running benches/sqlparser_bench.rs (target/release/deps/sqlparser_bench-90367034c12b9cef)
sqlparser-rs parsing benchmark/sqlparser::select
                        time:   [257.62 ns 258.12 ns 258.69 ns]
# With SmallVec::new()  ------------------------------------------------

sqlparser-rs parsing benchmark/sqlparser::select
                        time:   [3.9573 µs 3.9604 µs 3.9654 µs]
                        change: [+1443.7% +1449.0% +1453.8%] (p = 0.00 < 0.05)
                        Performance has regressed.

[pereman2]

@gwenn ping :)

[gwenn]

@pereman2 pong :)

[gwenn]

I can reproduce your results:

sqlparser_bench % cargo bench # master
sqlparser-rs parsing benchmark/sqlparser::select
                        time:   [15.510 µs 16.289 µs 17.324 µs]
Found 11 outliers among 100 measurements (11.00%)
  8 (8.00%) high mild
  3 (3.00%) high severe
sqlparser-rs parsing benchmark/sqlparser::with_select
                        time:   [31.396 µs 32.301 µs 33.468 µs]
Found 8 outliers among 100 measurements (8.00%)
  5 (5.00%) high mild
  3 (3.00%) high severe

sqlparser_bench % cargo bench # your branch
sqlparser-rs parsing benchmark/sqlparser::select
                        time:   [433.49 ns 435.21 ns 437.12 ns]
                        change: [-97.356% -97.272% -97.198%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 11 outliers among 100 measurements (11.00%)
  3 (3.00%) high mild
  8 (8.00%) high severe
sqlparser-rs parsing benchmark/sqlparser::with_select
                        time:   [445.34 ns 447.70 ns 450.63 ns]
                        change: [-98.615% -98.579% -98.548%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 10 outliers among 100 measurements (10.00%)
  3 (3.00%) high mild
  7 (7.00%) high severe

[pereman2]

Nice

[gwenn]

In fact, you were benchmarking Parser::new + StackOverflow...
See f83a162

Benchmarking sqlparser-rs parsing benchmark/sqlparser::select: Warming up for 3.0000 sthread 'main' panicked at benches/sqlparser_bench.rs:24:35:
called `Result::unwrap()` on an `Err` value: ParserError(StackOverflow, Some((1, 7)))
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::result::unwrap_failed
   3: criterion::bencher::Bencher<M>::iter
   4: <criterion::routine::Function<M,F,T> as criterion::routine::Routine<M,T>>::warm_up
   5: criterion::routine::Routine::sample
   6: criterion::analysis::common
   7: criterion::benchmark_group::BenchmarkGroup<M>::bench_with_input
   8: sqlparser_bench::main

[pereman2]

In fact, you were benchmarking Parser::new + StackOverflow... See f83a162

Benchmarking sqlparser-rs parsing benchmark/sqlparser::select: Warming up for 3.0000 sthread 'main' panicked at benches/sqlparser_bench.rs:24:35:
called `Result::unwrap()` on an `Err` value: ParserError(StackOverflow, Some((1, 7)))
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::result::unwrap_failed
   3: criterion::bencher::Bencher<M>::iter
   4: <criterion::routine::Function<M,F,T> as criterion::routine::Routine<M,T>>::warm_up
   5: criterion::routine::Routine::sample
   6: criterion::analysis::common
   7: criterion::benchmark_group::BenchmarkGroup<M>::bench_with_input
   8: sqlparser_bench::main

oh wow didn't notice

[gwenn]

But you made sqlite3-parser on par with sqlparser-rs:
https://github.com/gwenn/lemon-rs/blob/master/sqlparser_bench/README.md
Thanks.