restore: reuse bytes.Buffer

[lonng]

What problem does this PR solve?

restore: reuse bytes.Buffer in chunk.restore

benchmark (SQL file: 1529669bytes ~1.5KB, Chunk size: 64KB, Rows: 223):

tidb-lightning/lightning/restore/restore_test.go

Line 55 in be8eb67

func BenchmarkChunkRestoreReuseBuffer(b *testing.B) {

pkg: github.com/pingcap/tidb-lightning/lightning/restore
BenchmarkChunkRestoreReuseBuffer-8           500           2506818 ns/op         8996015 B/op        816 allocs/op
BenchmarkChunkRestoreReuseBuffer2-8         1000           2100410 ns/op         5665507 B/op        630 allocs/op
PASS

benchmark (SQL file: 1GB, Chunk size: 64KB):

goos: darwin
goarch: amd64
pkg: github.com/pingcap/tidb-lightning/lightning/restore
BenchmarkChunkRestoreReuseBuffer-8             1        2829461699 ns/op        6504717832 B/op  1342278 allocs/op
BenchmarkChunkRestoreReuseBuffer2-8            1        1476907662 ns/op        3284208384 B/op  1114627 allocs/op
PASS

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test

Code changes

Side effects

Related changes

[sre-bot]

Hi contributor, thanks for your PR.

This patch needs to be approved by someone of admins. They should reply with "/ok-to-test" to accept this PR for running test automatically.

[lonng]

/run-all-tests

[lonng]

/run-integration-test

[kennytm]

LGTM.

PTAL @csuzhangxc

[IANTHEREAL]

LGTM

[winkyao]

LGTM

[sre-bot]

Hi contributor, thanks for your PR.

This patch needs to be approved by someone of admins. They should reply with "/ok-to-test" to accept this PR for running test automatically.