From 2181653be637cdcc7a6efee8ec0a719df1d83c00 Mon Sep 17 00:00:00 2001 From: Justin Nuß Date: Tue, 25 Apr 2017 21:23:34 +0200 Subject: encoding/csv: add option to reuse slices returned by Read MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In many cases the records returned by Reader.Read will only be used between calls to Read and become garbage once a new record is read. In this case, instead of allocating a new slice on each call to Read, we can reuse the last allocated slice for successive calls to avoid unnecessary allocations. This change adds a new field ReuseRecord to the Reader struct to enable this reuse. ReuseRecord is false by default to avoid breaking existing code which dependss on the current behaviour. I also added 4 new benchmarks, corresponding to the existing Read benchmarks, which set ReuseRecord to true. Benchstat on my local machine (old is ReuseRecord = false, new is ReuseRecord = true) name old time/op new time/op delta Read-8 2.75µs ± 2% 1.88µs ± 1% -31.52% (p=0.000 n=14+15) ReadWithFieldsPerRecord-8 2.75µs ± 0% 1.89µs ± 1% -31.43% (p=0.000 n=13+13) ReadWithoutFieldsPerRecord-8 2.77µs ± 1% 1.88µs ± 1% -32.06% (p=0.000 n=15+15) ReadLargeFields-8 55.4µs ± 1% 54.2µs ± 0% -2.07% (p=0.000 n=15+14) name old alloc/op new alloc/op delta Read-8 664B ± 0% 24B ± 0% -96.39% (p=0.000 n=15+15) ReadWithFieldsPerRecord-8 664B ± 0% 24B ± 0% -96.39% (p=0.000 n=15+15) ReadWithoutFieldsPerRecord-8 664B ± 0% 24B ± 0% -96.39% (p=0.000 n=15+15) ReadLargeFields-8 3.94kB ± 0% 2.98kB ± 0% -24.39% (p=0.000 n=15+15) name old allocs/op new allocs/op delta Read-8 18.0 ± 0% 8.0 ± 0% -55.56% (p=0.000 n=15+15) ReadWithFieldsPerRecord-8 18.0 ± 0% 8.0 ± 0% -55.56% (p=0.000 n=15+15) ReadWithoutFieldsPerRecord-8 18.0 ± 0% 8.0 ± 0% -55.56% (p=0.000 n=15+15) ReadLargeFields-8 24.0 ± 0% 12.0 ± 0% -50.00% (p=0.000 n=15+15) Fixes #19721 Change-Id: I79b14128bb9bb3465f53f40f93b1b528a9da6f58 Reviewed-on: https://go-review.googlesource.com/41730 Reviewed-by: Brad Fitzpatrick Run-TryBot: Brad Fitzpatrick TryBot-Result: Gobot Gobot --- src/encoding/csv/reader_test.go | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) (limited to 'src/encoding/csv/reader_test.go') diff --git a/src/encoding/csv/reader_test.go b/src/encoding/csv/reader_test.go index 7b3aca4c5f..5ab1b61256 100644 --- a/src/encoding/csv/reader_test.go +++ b/src/encoding/csv/reader_test.go @@ -24,6 +24,7 @@ var readTests = []struct { LazyQuotes bool TrailingComma bool TrimLeadingSpace bool + ReuseRecord bool Error string Line int // Expected error line if != 0 @@ -260,6 +261,15 @@ x,,, {"c", "d", "e"}, }, }, + { + Name: "ReadAllReuseRecord", + ReuseRecord: true, + Input: "a,b\nc,d", + Output: [][]string{ + {"a", "b"}, + {"c", "d"}, + }, + }, } func TestRead(t *testing.T) { @@ -274,6 +284,7 @@ func TestRead(t *testing.T) { r.LazyQuotes = tt.LazyQuotes r.TrailingComma = tt.TrailingComma r.TrimLeadingSpace = tt.TrimLeadingSpace + r.ReuseRecord = tt.ReuseRecord if tt.Comma != 0 { r.Comma = tt.Comma } @@ -369,3 +380,23 @@ xxxxxxxxxxxxxxxxxxxxxxxx,yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy,zzzzzzzzzzzzzzzzzzzzzz xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx,yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy,zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww,vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv `, 3)) } + +func BenchmarkReadReuseRecord(b *testing.B) { + benchmarkRead(b, func(r *Reader) { r.ReuseRecord = true }, benchmarkCSVData) +} + +func BenchmarkReadReuseRecordWithFieldsPerRecord(b *testing.B) { + benchmarkRead(b, func(r *Reader) { r.ReuseRecord = true; r.FieldsPerRecord = 4 }, benchmarkCSVData) +} + +func BenchmarkReadReuseRecordWithoutFieldsPerRecord(b *testing.B) { + benchmarkRead(b, func(r *Reader) { r.ReuseRecord = true; r.FieldsPerRecord = -1 }, benchmarkCSVData) +} + +func BenchmarkReadReuseRecordLargeFields(b *testing.B) { + benchmarkRead(b, func(r *Reader) { r.ReuseRecord = true }, strings.Repeat(`xxxxxxxxxxxxxxxx,yyyyyyyyyyyyyyyy,zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww,vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv +xxxxxxxxxxxxxxxxxxxxxxxx,yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy,zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww,vvvv +,,zzzz,wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww,vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv +xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx,yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy,zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz,wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww,vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv +`, 3)) +} -- cgit v1.3