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database.go
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database.go
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package main
import (
"database/sql"
"errors"
"fmt"
"io"
"log"
"net/http"
"os"
"path/filepath"
_ "github.com/mattn/go-sqlite3"
)
func openDatabase(path string) (*sql.DB, error) {
options :=
"?" + "_busy_timeout=10000" +
"&" + "_case_sensitive_like=OFF" +
"&" + "_foreign_keys=ON" +
"&" + "_journal_mode=OFF" +
"&" + "_locking_mode=NORMAL" +
"&" + "mode=rw" +
"&" + "_synchronous=OFF"
db, err := sql.Open("sqlite3", path+options)
if err != nil {
// handle the error here
log.Fatalf("open database: %v\n", err)
return nil, err
}
return db, nil
}
func createDatabase(path string) (*sql.DB, error) {
// delete exist database
if _, err := os.Stat(path); os.IsNotExist(err) {
os.Remove(path)
}
create, err := os.Create(path)
if err != nil {
log.Fatalf("os.create: %v\n", err)
return nil, err
}
create.Close()
// create a dababase
db, err := openDatabase(path)
if err != nil {
log.Fatalf("open database: %v\n", err)
return nil, err
}
tx, err := opentransaction(db)
if err != nil {
log.Fatalf("create opentransaction:%v\n", err)
return nil, err
}
_, err = tx.Exec("create table pairs (key text, value text)")
if err != nil {
log.Fatalf("db.Exec: %v\n", err)
return nil, err
}
if err = tx.Commit(); err != nil {
log.Fatalf("create tx.Commit: %v\n", err)
return nil, err
}
defer db.Close()
return db, nil
}
func opentransaction(database *sql.DB) (*sql.Tx, error) {
tx, err := database.Begin()
if err != nil {
log.Fatalf("database.Begin: %v\n", err)
return nil, err
}
return tx, nil
}
func splitDatabase(source, outputDir, outputPattern string, m int) ([]string, error) {
// load the data
var count int
var key, value string
var list [][]string
var i int
db, err := openDatabase(source)
if err != nil {
log.Fatalf("open database: %v\n", err)
return nil, err
}
defer db.Close()
transaction, err := opentransaction(db)
if err != nil {
log.Fatalf("open transaction: %v\n", err)
return nil, err
}
rows, err := transaction.Query("select key, value from pairs")
if err != nil {
log.Fatalf("transaction.Query: %v\n", err)
return nil, err
}
defer rows.Close()
for rows.Next() {
// read the data using rows.Scan
// process the result
if err := rows.Scan(&key, &value); err != nil {
log.Fatalf("rows.Scan: %v\n", err)
return nil, err
}
list = append(list, []string{})
list[i] = append(list[i], key)
list[i] = append(list[i], value)
i++
count++
}
if err = rows.Err(); err != nil {
// handle the error
return nil, err
}
if count < m {
countErr := errors.New("read row count is smaller than m\n")
return nil, countErr
}
// create the output files
var outputDBs []string
count = 0
for i := 0; i < m; i++ {
newPath := filepath.Join(outputDir, fmt.Sprintf(outputPattern, i))
if _, err := createDatabase(newPath); err != nil {
log.Fatalf("create database: %v\n", err)
return nil, err
}
outputDBs = append(outputDBs, newPath)
db, err := openDatabase(newPath) // open the output database files
if err != nil {
log.Fatalf("open database: %v\n", err)
return nil, err
}
defer db.Close()
// insert into the output database files
listIndex := i
for listIndex < len(list) {
key = list[listIndex][0]
value = list[listIndex][1]
_, err = db.Exec(`insert into pairs (key, value) values (?, ?)`, key, value)
if err != nil {
log.Fatalf("db.Exec: %v\n", err)
return nil, err
}
defer db.Close()
count++
listIndex += m
}
db.Close()
if count < m {
countErr := errors.New("insert row count is smaller than m\n")
return nil, countErr
}
}
return outputDBs, nil
}
func mergeDatabases(urls []string, path string, temp string) (*sql.DB, error) {
// Create a new output database
db, err := createDatabase(path)
if err != nil {
return nil, err
}
if db, err = openDatabase(path); err != nil {
return nil, err
}
for i := range urls {
if err := download(urls[i], temp); err != nil {
log.Fatalf("download: %v\n", err)
return nil, err
}
_, fileName := filepath.Split(urls[i])
tempFile := filepath.Join(temp, fileName)
if err = gatherInto(db, tempFile); err != nil {
return nil, err
}
defer db.Close()
}
return db, nil
}
// out.db, pathname(input file)
func gatherInto(db *sql.DB, path string) error {
dir, fileName := filepath.Split(path)
os.Chdir(dir)
_, err := db.Exec("attach ? as merge;insert into pairs select * from merge.pairs;detach merge;", fileName)
if err != nil {
return err
}
os.Remove(path)
return nil
}
// DownloadFile will download a url to a local file. It's efficient because it will
// write as it downloads and not load the whole file into memory.
func download(url, path string) error {
// Get the data
resp, err := http.Get(url)
if err != nil {
log.Fatalf("download Get: %v\n", err)
return err
}
defer resp.Body.Close()
// Create the file
_, fileName := filepath.Split(url)
path = filepath.Join(path, fileName)
out, err := os.Create(path)
if err != nil {
log.Fatalf("download os.Create: %v\n", err)
return err
}
defer out.Close()
// Write the body to file
_, err = io.Copy(out, resp.Body)
if err != nil {
log.Fatalf("download io.Copy: %v\n", err)
return err
}
return nil
}