我最近用 golang 重新实现了我的项目。该项目是用 C++ 实现的。当我完成代码并进行性能测试时。我对结果感到震惊。当我用 C++ 查询数据库时，我可以在 5 分钟内得到 1.3 亿行结果。但是对于 golang，它几乎是 45 分钟。但是当我将代码从项目中分离出来并构建代码片段时，它会在 2 分钟内完成。为什么它们的性能结果会有如此巨大的差异？

我的代码片段: https://gist.github.com/pyanfield/2651d23311901b33c5723b7de2364148

package main

import (
    "database/sql"
    "fmt"
    "runtime"
    "strconv"
    "time"

    _ "github.com/go-sql-driver/mysql"
)

func main() {
    runtime.GOMAXPROCS(runtime.NumCPU())
    // defer profile.Start(profile.CPUProfile, profile.ProfilePath(".")).Stop()
    dbRead, err := connectDB("test:test@tcp(127.0.0.1:3306)/test_oltp?charset=utf8&readTimeout=600s&writeTimeout=600s")
    if err != nil {
        fmt.Printf("Error happend when connecting to DB. %s\n", err.Error())
        return
    }
    defer dbRead.Close()
    dbRead.SetMaxIdleConns(0)
    dbRead.SetMaxOpenConns(100)

    query := fmt.Sprintf("WHERE company_id in (11,22,33,44,55,66,77,88,99,00,111,222,333,4444,555,666,777,888,999)")

    relations := getRelations(dbRead, query)
}
func connectDB(addr string) (*sql.DB, error) {
    db, err := sql.Open("mysql", addr)
    if err != nil {
        return nil, err
    }
    if err = db.Ping(); err != nil {
        return nil, err
    }
    return db, nil
}

type Relation struct {
    childId  int64 
    parentId int64 
}

func getRelations(db *sql.DB, where string)[]Relation {
    begin := time.Now()

    var err error
    var rows *sql.Rows
    query := fmt.Sprintf("SELECT `child_id`, `parent_id` FROM `test_relations` %s", where)
    rows, err = db.Query(query)
    if err != nil {
        fmt.Println("query error:", err.Error())
        return nil
    }
    defer rows.Close()

    columns, err := rows.Columns()
    buffer := make([]sql.RawBytes, len(columns))
    scanArgs := make([]interface{}, len(buffer))
    for i := range scanArgs {
        scanArgs[i] = &buffer[i]
    }

    relations := []Relation{}
    relation := Relation{}
    for rows.Next() {
        if err = rows.Scan(scanArgs...); err != nil {
            fmt.Println("scan:", err.Error())
            return nil
        }
        relation.parentId, _ = strconv.ParseInt(string(buffer[1]), 10, 64)
        relation.childId, _ = strconv.ParseInt(string(buffer[0]), 10, 64)

        relations = append(relations, relation)
    }

    if err = rows.Err(); err != nil {
        fmt.Println("next error:", err.Error())
        return nil
    }
    fmt.Printf(">>> getRelations cost: %s\n", time.Since(begin).String())
    // output :>>> getRelations cost:1m45.791047s
    return relations
    // len(relations): 131123541
}

更新: 我的go版本是1.6。我得到的cpu配置文件如下: 代码段简介top20:

    75.67s of 96.82s total (78.16%)
Dropped 109 nodes (cum <= 0.48s)
Showing top 20 nodes out of 82 (cum >= 12.04s)
      flat  flat%   sum%        cum   cum%
    11.85s 12.24% 12.24%     11.85s 12.24%  runtime.memmove
    10.28s 10.62% 22.86%     20.01s 20.67%  runtime.mallocgc
     5.82s  6.01% 28.87%      5.82s  6.01%  strconv.ParseUint
     5.79s  5.98% 34.85%      5.79s  5.98%  runtime.futex
     3.42s  3.53% 38.38%     10.28s 10.62%  github.com/go-sql-driver/mysql.(*buffer).readNext
     3.42s  3.53% 41.91%      6.38s  6.59%  runtime.scang
     3.37s  3.48% 45.39%     36.97s 38.18%  github.com/go-sql-driver/mysql.(*textRows).readRow
     3.37s  3.48% 48.87%      3.37s  3.48%  runtime.memclr
     3.20s  3.31% 52.18%      3.20s  3.31%  runtime.heapBitsSetType
     3.02s  3.12% 55.30%      7.36s  7.60%  database/sql.convertAssign
     2.96s  3.06% 58.36%      3.02s  3.12%  runtime.(*mspan).sweep.func1
     2.53s  2.61% 60.97%      2.53s  2.61%  runtime._ExternalCode
     2.39s  2.47% 63.44%      2.96s  3.06%  runtime.readgstatus
     2.24s  2.31% 65.75%      8.06s  8.32%  strconv.ParseInt
     2.21s  2.28% 68.03%      5.24s  5.41%  runtime.heapBitsSweepSpan
     2.15s  2.22% 70.25%      7.68s  7.93%  runtime.rawstring
     2.06s  2.13% 72.38%      3.18s  3.28%  github.com/go-sql-driver/mysql.readLengthEncodedString
     1.95s  2.01% 74.40%     12.23s 12.63%  github.com/go-sql-driver/mysql.(*mysqlConn).readPacket
     1.83s  1.89% 76.29%     79.42s 82.03%  main.Relations
     1.81s  1.87% 78.16%     12.04s 12.44%  runtime.slicebytetostring

项目cpu配置文件top20:

     (pprof) top20
38.71mins of 42.82mins total (90.40%)
Dropped 334 nodes (cum <= 0.21mins)
Showing top 20 nodes out of 76 (cum >= 1.35mins)
      flat  flat%   sum%        cum   cum%
 12.02mins 28.07% 28.07%  12.48mins 29.15%  runtime.addspecial
  5.95mins 13.89% 41.96%  15.08mins 35.21%  runtime.pcvalue
  5.26mins 12.29% 54.25%   5.26mins 12.29%  runtime.readvarint
  2.60mins  6.08% 60.32%   7.87mins 18.37%  runtime.step
  1.98mins  4.62% 64.94%  19.45mins 45.43%  runtime.gentraceback
  1.65mins  3.86% 68.80%   1.65mins  3.86%  runtime/internal/atomic.Xchg
  1.57mins  3.66% 72.46%   2.93mins  6.84%  runtime.(*mspan).sweep
  1.52mins  3.54% 76.01%   1.78mins  4.15%  runtime.findfunc
  1.41mins  3.30% 79.31%   1.42mins  3.31%  runtime.markrootSpans
  1.13mins  2.64% 81.95%   1.13mins  2.64%  runtime.(*fixalloc).alloc
  0.64mins  1.50% 83.45%   0.64mins  1.50%  runtime.duffcopy
  0.46mins  1.08% 84.53%   0.46mins  1.08%  runtime.findmoduledatap
  0.44mins  1.02% 85.55%   0.44mins  1.02%  runtime.fastrand1
  0.42mins  0.97% 86.52%  15.49mins 36.18%  runtime.funcspdelta
  0.38mins  0.89% 87.41%  36.02mins 84.13%  runtime.mallocgc
  0.30mins   0.7% 88.12%   0.78mins  1.83%  runtime.scanobject
  0.26mins   0.6% 88.72%   0.32mins  0.74%  runtime.stkbucket
  0.26mins   0.6% 89.32%   0.26mins   0.6%  runtime.memmove
  0.23mins  0.55% 89.86%   0.23mins  0.55%  runtime.heapBitsForObject
  0.23mins  0.53% 90.40%   1.35mins  3.15%  runtime.lock

最佳答案

我得到了答案并想分享它。这是我的错误造成的。以前有时，我尝试添加内存配置文件并设置 运行时。 MemProfileRate=1 在我的 init 方法中。但是我忘了把它重置为一个合理的值。我每次检查代码时都忽略了这个方法。从我的项目中删除此设置后，它恢复正常，并且花了将近 5~6 分钟来查询这 130M 数据。速度非常接近 C++ 版本。我的建议是，除非您确定要这样做，否则在设置 runtime.MemProfileRate=1 时请小心，并记得将其重置。

关于c++ - 使用相同的 golang 片段查询 mysql 数据库的巨大性能差异，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37500878/