mapserver/server/db/sqlite.go

package db

import (
	"database/sql"
	_ "github.com/mattn/go-sqlite3"
	"github.com/sirupsen/logrus"
	"mapserver/coords"
	"time"
)

/*
sqlite extract: https://stackoverflow.com/questions/15448373/how-to-dump-a-file-stored-in-a-sqlite-database-as-a-blob
sqlite3 my.db "SELECT writefile('object0.gz', MyBlob) FROM MyTable WHERE id = 1"
*/

const migrateScript = `
alter table blocks add mtime integer default 0;
create index blocks_mtime on blocks(mtime);

CREATE TRIGGER update_blocks_mtime_insert after insert on blocks for each row
begin
update blocks set mtime = strftime('%s', 'now') where pos = new.pos;
end;

CREATE TRIGGER update_blocks_mtime_update after update on blocks for each row
begin
update blocks set mtime = strftime('%s', 'now') where pos = old.pos;
end;
`

//TODO: initial run: https://stackoverflow.com/questions/14468586/efficient-paging-in-sqlite-with-millions-of-records
//TODO: postgres test

type Sqlite3Accessor struct {
	db       *sql.DB
	filename string
}

func (db *Sqlite3Accessor) Migrate() error {

	//RW connection
	rwdb, err := sql.Open("sqlite3", db.filename+"?mode=rw")
	if err != nil {
		return err
	}

	defer rwdb.Close()

	hasMtime := true
	_, err = rwdb.Query("select max(mtime) from blocks")
	if err != nil {
		hasMtime = false
	}

	if !hasMtime {
		log.WithFields(logrus.Fields{"filename": db.filename}).Info("Migrating database")
		start := time.Now()
		_, err = rwdb.Exec(migrateScript)
		if err != nil {
			return err
		}
		t := time.Now()
		elapsed := t.Sub(start)
		log.WithFields(logrus.Fields{"elapsed": elapsed}).Info("Migration completed")
	}

	return nil
}

func convertRows(pos int64, data []byte, mtime int64) Block {
	c := coords.PlainToCoord(pos)
	return Block{Pos: c, Data: data, Mtime: mtime}
}

const getLastBlockQuery = `
select pos,data,mtime
from blocks b
where b.mtime > ?
and b.pos > ?
order by b.pos asc, b.mtime asc
limit ?
`

func (db *Sqlite3Accessor) FindBlocks(lastpos coords.MapBlockCoords, lastmtime int64, limit int) ([]Block, error) {
	blocks := make([]Block, 0)
	pc := coords.CoordToPlain(lastpos)

	rows, err := db.db.Query(getLastBlockQuery, lastmtime, pc, limit)
	if err != nil {
		return nil, err
	}

	defer rows.Close()

	for rows.Next() {
		var pos int64
		var data []byte
		var mtime int64

		err = rows.Scan(&pos, &data, &mtime)
		if err != nil {
			return nil, err
		}

		mb := convertRows(pos, data, mtime)
		blocks = append(blocks, mb)
	}

	return blocks, nil
}

const countBlocksQuery = `
select count(*) from blocks b where b.mtime >= ? and b.mtime <= ?
`

func (db *Sqlite3Accessor) CountBlocks(frommtime, tomtime int64) (int, error) {
	rows, err := db.db.Query(countBlocksQuery, frommtime, tomtime)
	if err != nil {
		return 0, err
	}

	defer rows.Close()

	if rows.Next() {
		var count int64

		err = rows.Scan(&count)
		if err != nil {
			return 0, err
		}

		return int(count), nil
	}

	return 0, nil
}


const getBlockQuery = `
select pos,data,mtime from blocks b where b.pos = ?
`

func (db *Sqlite3Accessor) GetBlock(pos coords.MapBlockCoords) (*Block, error) {
	ppos := coords.CoordToPlain(pos)

	rows, err := db.db.Query(getBlockQuery, ppos)
	if err != nil {
		return nil, err
	}

	defer rows.Close()

	if rows.Next() {
		var pos int64
		var data []byte
		var mtime int64

		err = rows.Scan(&pos, &data, &mtime)
		if err != nil {
			return nil, err
		}

		mb := convertRows(pos, data, mtime)
		return &mb, nil
	}

	return nil, nil
}

func NewSqliteAccessor(filename string) (*Sqlite3Accessor, error) {
	db, err := sql.Open("sqlite3", filename+"?mode=ro")
	if err != nil {
		return nil, err
	}

	sq := &Sqlite3Accessor{db: db, filename: filename}
	return sq, nil
}