Stowage/go
2
0
Fork 0
mirror of https://github.com/golang/go.git synced 2025-12-08 06:10:04 +00:00
Code Issues Projects Releases Packages Wiki Activity

encoding/csv: add option to reuse slices returned by Read

Browse source 
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 <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Justin Nuß 2017-04-25 21:23:34 +02:00 • committed by Brad Fitzpatrick
parent ba8ff87dbe
commit 2181653be6
2 changed files with 81 additions and 21 deletions
Download patch file Download diff file Expand all files Collapse all files

31
src/encoding/csv/reader_test.go
View file

@ -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))
}