Use pointers instead of binary encoding

[jarifibrahim]

The change improves encoding/decoding performance by 4X. See https://gist.github.com/jarifibrahim/30237927ff3a4b200d4907c97bd93f41 for benchmark code.

name                        time/op
EncodingSingle/Binary-16    4.02ns ± 1%
EncodingSingle/Slice-16     0.83ns ± 0%
Encodingu32Slice/Binary-16  9.52µs ± 1%
Encodingu32Slice/Slice-16   0.95ns ± 0%

The change also improves the performance of existing benchmarks.

name             old time/op  new time/op  delta
Read-16           153ms ± 1%   145ms ± 1%  -5.09%  (p=0.008 n=5+5)
ReadAndBuild-16   1.01s ± 1%   0.97s ± 3%  -4.04%  (p=0.008 n=5+5)
ReadMerged-16     980ms ± 1%   980ms ± 1%    ~     (p=1.000 n=5+5)
RandomRead-16    2.73µs ± 0%  2.65µs ± 1%  -2.73%  (p=0.008 n=5+5)

Inspired by pingcap@0b03ef0

---

This change is 

[manishrjain]

Reviewable status: 0 of 6 files reviewed, 2 unresolved discussions (waiting on @ashish-goswami, @jarifibrahim, and @manishrjain)

---

structs.go, line 39 at r1 (raw file):

func (p valuePointer) Encode() []byte {
	b := make([]byte, vptrSize)
	*(*valuePointer)(unsafe.Pointer(&b[0])) = p

How fast is this? Any benchmarks compared to previous approach?

---

table/builder.go, line 312 at r1 (raw file):

}

func u32SliceToBytes(u32s []uint32) []byte {

How fast do things get here? Can you benchmark this code for 2 things:

1. Building a slice of []uint32 -> bytes. Diff in speed between two approaches.
2. Accessing via getOffset and equivalent. Diff in speed between these two approaches.

[pullrequest]

✅ A review job has been created and sent to the PullRequest network.

---

@jarifibrahim you can click here to see the review status or cancel the code review job - or - cancel by adding [!pr] to the title of the pull request.

[jarifibrahim]

Reviewable status: 0 of 6 files reviewed, 2 unresolved discussions (waiting on @ashish-goswami and @manishrjain)

---

structs.go, line 39 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

How fast is this? Any benchmarks compared to previous approach?

Binary encoding takes 4.03ns while slice pointer takes 0.83ns
See https://gist.github.com/jarifibrahim/30237927ff3a4b200d4907c97bd93f41 for benchmark code

---

table/builder.go, line 312 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

How fast do things get here? Can you benchmark this code for 2 things:

1. Building a slice of []uint32 -> bytes. Diff in speed between two approaches.
2. Accessing via getOffset and equivalent. Diff in speed between these two approaches.

For 1. see https://gist.github.com/jarifibrahim/30237927ff3a4b200d4907c97bd93f41 for benchmark code

name                        time/op
EncodingSingle/Binary-16    4.03ns ± 1%
EncodingSingle/Slice-16     0.83ns ± 1%
Encodingu32Slice/Binary-16  9.48µs ± 1%
Encodingu32Slice/Slice-16   0.94ns ± 0%

For 2, each getOffSet call should take 4.03ns while and converting the entire slice via pointers takes 0.94ns

[manishrjain]

Got a few comments.

Reviewed 1 of 6 files at r1, 5 of 5 files at r2.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @ashish-goswami, @jarifibrahim, and @manishrjain)

---

structs.go, line 39 at r1 (raw file):

Previously, jarifibrahim (Ibrahim Jarif) wrote…

Binary encoding takes 4.03ns while slice pointer takes 0.83ns
See https://gist.github.com/jarifibrahim/30237927ff3a4b200d4907c97bd93f41 for benchmark code

Add a comment here that you're copying the contents of p into b.

---

structs.go, line 40 at r2 (raw file):

	b := make([]byte, vptrSize)
	*(*valuePointer)(unsafe.Pointer(&b[0])) = p
	return b[:]

return b

---

table/builder.go, line 281 at r2 (raw file):

Previously, ashish-goswami (Ashish Goswami) wrote…

We can move these functions to y package so that these can be reused.

Move the decode equivalent next to encoder func.

[jarifibrahim]

Reviewable status: 2 of 9 files reviewed, 4 unresolved discussions (waiting on @ashish-goswami and @manishrjain)

---

structs.go, line 39 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

Add a comment here that you're copying the contents of p into b.

Done.

---

structs.go, line 40 at r2 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

return b

Done.

---

table/builder.go, line 281 at r2 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

Move the decode equivalent next to encoder func.

Done.

[jarifibrahim]

Reviewed 2 of 5 files at r2, 5 of 6 files at r3, 2 of 2 files at r4.
Dismissed @ashish-goswami and @manishrjain from 4 discussions.
Reviewable status: complete! all files reviewed, all discussions resolved